The study, led by researchers from Xiamen University in China, investigates the protective effects of hydrogen sulfide, a gasotransmitter that has long been recognized for its antioxidant and anti-inflammatory properties. In the context of diabetes, vascular smooth muscle cells undergo a pathological phenotypic switch, becoming more proliferative and migratory, which contributes to the thickening and stiffening of arterial walls. The researchers sought to understand how hydrogen sulfide might counteract these abnormal cellular behaviors, aiming to identify specific molecular targets that could serve as therapeutic interventions for diabetic vascular complications.

Using a combination of in vivo and in vivo models, the team utilized type 2 diabetes mellitus mice and mouse aortic vascular smooth muscle cells cultured under high-glucose and high-fat conditions to mimic the metabolic environment of diabetic patients. Their initial observations revealed a critical deficiency in the diabetic state: a marked decrease in the expression of cystathionine gamma-lyase, the primary enzyme responsible for synthesizing hydrogen sulfide in the body. This reduction in endogenous hydrogen sulfide production was directly correlated with increased oxidative stress and the activation of the NLRP3 inflammasome, a complex protein structure that plays a key role in initiating inflammation.

The activation of the NLRP3 inflammasome is a central event in the pathogenesis of diabetic vasculopathy, as it triggers the release of pro-inflammatory cytokines that exacerbate tissue damage. The researchers found that when hydrogen sulfide levels were low, vascular smooth muscle cells exhibited heightened proliferative and migratory activity, further contributing to vascular remodeling. To test the hypothesis that hydrogen sulfide could reverse these pathological changes, the team administered sodium hydrosulfide, a stable hydrogen sulfide donor, to the experimental models. The results were striking: the introduction of hydrogen sulfide effectively reversed the elevated oxidative stress and suppressed the activation of the NLRP3 inflammasome, thereby reducing the abnormal proliferation and migration of vascular smooth muscle cells.

However, the study went beyond confirming the protective effects of hydrogen sulfide to elucidate the specific molecular mechanism behind these benefits. The researchers focused on a post-translational modification known as S-sulfhydration, a process where hydrogen sulfide adds a sulfane sulfur group to cysteine residues of proteins. Through detailed protein analysis, they identified that hydrogen sulfide promotes the S-sulfhydration of thioredoxin reductase 1, a key enzyme in the cellular redox system. This modification occurs specifically at the Cys611 residue of thioredoxin reductase 1, a site that is crucial for the enzyme’s catalytic activity and its interaction with other redox-regulating proteins.

The S-sulfhydration of thioredoxin reductase 1 at Cys611 has profound downstream effects on the thioredoxin 1-thioredoxin-interacting protein-NLRP3 signaling axis. Thioredoxin 1 is a major intracellular antioxidant that binds to and inhibits thioredoxin-interacting protein, which is a known activator of the NLRP3 inflammasome. By enhancing the activity of thioredoxin reductase 1 through S-sulfhydration, hydrogen sulfide ensures that thioredoxin 1 remains in its active, reduced state. This active thioredoxin 1 effectively sequesters thioredoxin-interacting protein, preventing it from activating the NLRP3 inflammasome. Consequently, the entire inflammatory cascade is dampened, leading to a reduction in the production of inflammatory mediators that drive vascular damage.

To validate this mechanism, the researchers employed pharmacological inhibition and rescue experiments. They used specific inhibitors to block the S-sulfhydration of thioredoxin reductase 1 and observed that the protective effects of hydrogen sulfide were significantly diminished. Conversely, when they restored the S-sulfhydration status of thioredoxin reductase 1, the anti-inflammatory and anti-proliferative effects were reinstated. These experiments provided strong evidence that the S-sulfhydration of thioredoxin reductase 1 at Cys611 is not merely a byproduct of hydrogen sulfide exposure but is a critical regulatory step in the pathway that leads to vascular protection. This finding underscores the importance of specific post-translational modifications in mediating the biological effects of gasotransmitters.

The implications of this study extend beyond the immediate understanding of diabetic vasculopathy. By identifying the thioredoxin reductase 1 S-sulfhydration pathway as a key mediator of hydrogen sulfide’s protective effects, the researchers have highlighted a promising therapeutic target for the treatment of diabetic vascular complications. Drugs that can enhance the S-sulfhydration of thioredoxin reductase 1 or stabilize hydrogen sulfide levels could potentially offer new avenues for preventing or slowing the progression of vascular damage in diabetic patients. This approach could complement existing therapies that focus on glucose control and blood pressure management, providing a more comprehensive strategy for managing the complications of type 2 diabetes.

Furthermore, the study contributes to the growing body of evidence supporting the role of hydrogen sulfide in various physiological and pathological processes. While hydrogen sulfide has been studied in the context of cardiovascular protection, this research provides a detailed mechanistic insight into how it specifically targets the inflammatory pathways involved in diabetic vascular remodeling. The identification of the Cys611 residue as a critical site for S-sulfhydration offers a precise molecular target for future drug development. Understanding the intricate balance between oxidative stress, inflammation, and cellular redox regulation is essential for developing effective treatments for chronic diseases like diabetes, and this study makes a significant contribution to that understanding.

In conclusion, this research from Xiamen University provides a comprehensive mechanistic explanation for how hydrogen sulfide attenuates diabetic vascular remodeling. By demonstrating that hydrogen sulfide promotes the S-sulfhydration of thioredoxin reductase 1 at Cys611, thereby inhibiting the thioredoxin 1-thioredoxin-interacting protein-NLRP3 axis, the study reveals a novel pathway for vascular protection. These findings not only enhance our understanding of the molecular pathogenesis of diabetic vasculopathy but also open new possibilities for therapeutic interventions. As the global burden of type 2 diabetes continues to rise, identifying and targeting such specific molecular mechanisms will be crucial for improving patient outcomes and reducing the severity of its vascular complications.

Subject of Research: Mechanism of hydrogen sulfide-mediated protection against diabetic vascular remodeling via TrxR1 S-sulfhydration

Article Title: Hydrogen sulfide promotes S-sulfhydration of TrxR1 and attenuates diabetic vascular remodeling

Article References: Wei, Z., Wu, R., Ruan, J., Yang, J., Fu, X., Li, Y., Jiao, L., Xiang, L., Yu, D., Yan, G., Zhang, L., & Li, H. (2026). Hydrogen sulfide promotes S-sulfhydration of TrxR1 and attenuates diabetic vascular remodeling. Cell Death Discovery. https://doi.org/10.1038/s41420-026-03297-3

Image Credits: AI Generated

DOI: 10.1038/s41420-026-03297-3

Keywords: Hydrogen Sulfide, Diabetic Vasculopathy, TrxR1, S-sulfhydration, NLRP3 Inflammasome, Vascular Smooth Muscle Cells, Type 2 Diabetes, Oxidative Stress, Cell Death Discovery, Xiamen University, Hydrogen, sulfide

The research team, led by researchers studying the confluence of the Shakujii and Sumida Rivers, monitored salinity, dissolved oxygen, water level and rainfall at stations along both rivers from August to October 2017. The Shakujii River, a 25.2-kilometer waterway with a watershed of 61.6 square kilometers, drains a densely urbanized area served by 154 combined sewer outfall chambers that discharge domestic and storm water runoff. The Sumida River estuary, which flows through the deltaic lowland of central Tokyo into Tokyo Bay, receives fresh water from several tributaries including the Shakujii, and roughly 60 percent of its flow comes from treated sewage water. By tracking these parameters at ten-minute intervals, the researchers could link the hydrodynamics of the tidal estuary directly to the appearance of scum at the water surface.

Scum coverage was measured visually using a fixed video camera operated by the Kita City Office, which monitors the water surface upstream of the tidal area. The researchers divided a 25-meter by 20-meter section of the river into 100 grids of 2.5 by 2 meters and identified the percentage of scum in each grid every hour. This approach allowed continuous documentation of scum episodes, verification of resident complaints, and evaluation of how alternative management practices affect odor impacts. The data, collected from June to October 2017, were then classified according to dissolved oxygen ranges to compute the probability of scum occurrence under each condition.

The results revealed a clear relationship between oxygen depletion and scum formation. Under anoxic conditions, when dissolved oxygen fell between 0 and 1 milligram per liter, the probability of scum reached 75 percent. The probability dropped to 24 percent at dissolved oxygen levels of 2 to 4 milligrams per liter, 22 percent at 4 to 6 milligrams per liter, and only 12 percent when oxygen exceeded 6 milligrams per liter. Scum coverage was consistently higher when salinity was below 1 practical salinity unit and dissolved oxygen was below 6 milligrams per liter. These findings suggest that maintaining dissolved oxygen at or above 5 milligrams per liter for Class B and C rivers, or 7.5 milligrams per liter for Class A rivers, could substantially inhibit scum generation.

Rainfall emerged as the main precursor to scum episodes. From September 20 to 26, 2017, scum appeared three days after heavy rainfall totaling 64.75 millimeters, with hourly coverage ranging from 0.5 to 12.9 percent. The pattern is consistent with earlier observations that scum tends to appear two or three days after rainfall, when organic matter washed in from combined sewer systems is decomposed by microorganisms, consuming oxygen and generating the anaerobic gas that lifts sludge from the river bottom. During the study period, dissolved oxygen in the Shakujii River dropped from 5 to 1 milligram per liter within 12 hours after rainfall on September 18, and from 6 to 1 milligram per liter over 24 hours from September 23 to 24, likely because oxygen was consumed for the decomposition of organic matter.

The tidal dynamics of the estuary added another layer of complexity. Salinity in both rivers increased during neap tide and decreased during spring tide, a common estuarine condition. Saltwater from Tokyo Bay formed a stratified salt wedge during neap tide that flowed landward through the Sumida River and caused salinity intrusion into the Shakujii River. Notably, the researchers observed two salinity peaks for one semidiurnal tidal cycle in the Shakujii River, whereas the downstream Sumida station showed only one peak. The second peak in the Shakujii was attributed to residual salinity retained at the confluence, where the riverbed reaches its deepest elevation of minus 5.36 meters Arakawa Peil. When the tide turned from ebb to flood, a pressure wave pushed this retained saltwater upstream, carrying unoxygenated water with low dissolved oxygen into the tidal reach where scum is mainly generated.

Topography played a decisive role as well. The channel slope from the upstream to midstream Shakujii stations is nearly zero, and the upstream station faces a steep wall that prevents water transit during high tide. These features promote stagnant water conditions that are conducive to scum generation. Higher salinity also brings higher hydrogen sulfide, generated from the reduction of sulfate in seawater, which inhibits methane formation and produces stronger odor but less scum. Good estuarine mixing, the researchers conclude, is therefore favorable to avoid scum formation, and facilitating the proper transit of saltwater could diminish the problem.

To characterize the odors themselves, the team employed a Fragrance and Flavor Analyzer, an electronic nose machine that passes gas samples through ten metal oxide semiconductor sensors. Each odorous component produces a characteristic resistance change expressed as vector values, which are compared against nine calibrated reference gases to determine the similarity index and strength of each odor component. The machine generates an analog value of the odor index, which was converted into the actual olfactory sense through a regression equation. Human panelists performed simple olfactory measurements following the Ministry of the Environment method, comparing odor samples diluted with nitrogen against pure nitrogen to determine odor concentration, which was converted to the odor index as the logarithm of that concentration.

The odor analysis identified organic acids and hydrogen sulfide as the primary odor components of sediment in the Shakujii River, accounting for 14.2 percent and 14.4 percent respectively, followed by ester, sulfur and aldehyde compounds. In the Sumida River sediments, organic acids at 4 percent and sulfur at 1 percent were prominent but far weaker. The Shakujii River sediment exhibited the highest odor index of 25.5 and showed a 62.43 percent similarity with the scum sample, indicating that the bottom sediment is the likely source of the foul odor. The scum itself had the highest odor index of 27.8 and an odor concentration of 597.7, with panelists describing a sour pungent smell. The odor components resemble those from sanitary sewage discharged by combined sewer systems during heavy rainfall, with organic acids derived from automobile emissions and anthropogenic sources such as wood, agricultural waste and fossil fuels, and sulfur compounds coming from sulfur-containing organics in wastewater from restaurants, households and other facilities.

The study offers a template for addressing scum and odor issues in urban estuaries worldwide. Although measured gas concentrations may not precisely reflect human olfactory perception, the correlation of electronic nose results with human smell tests provides a reliable and repeatable method for identifying odor sources. The researchers recommend facilitating proper estuarine mixing, improving river topography where possible, and strictly implementing sewer discharge controls, especially during rainfall periods. As highly developed countries continue to struggle with river odor even when water quality standards are met, and developing countries may face the same problems in the future, the integration of on-site hydrodynamic monitoring with electronic nose technology offers new insights into how scum forms in actual river locations and how policy enforcement could enhance river water quality.

Subject of Research: Factors controlling scum formation and odor identification using an electronic nose in the tidal Shakujii and Sumida Rivers, Tokyo

Article Title: Factors affecting scum formation and the use of electronic nose to identify fundamental odor properties in urban estuaries

Article References: Casila, J. C., Okuyama, R., & Yokoyama, K. (2024). Factors affecting scum formation and the use of electronic nose to identify fundamental odor properties in urban estuaries. Estuarine Management and Technologies, 1(1), 39-56. https://doi.org/10.3897/emt.1.119588

Image Credits: AI Generated

DOI: 10.3897/emt.1.119588

Keywords: scum formation, electronic nose, urban estuary, dissolved oxygen, salinity intrusion, hydrogen sulfide, Tokyo rivers, odor monitoring, Factors, affecting, scum, formation

Mount Meager is an active, glacier-clad stratovolcano complex in the Garibaldi Volcanic Belt, part of the northern Cascade Volcanic Arc. Its last major explosive eruption occurred roughly 2,360 years ago, but the mountain remains restless, producing frequent landslides and venting volcanic gases through fumaroles on its glaciated slopes. The volcano is classified as a Very High threat volcano in Canada. Where fumarolic heat melts its way through glacial ice, void spaces form beneath the surface, creating glaciovolcanic cave systems. Only about six such cave areas have been described on Earth, and Mount Meager’s is unique among them in steadily releasing sulfur-rich gases rather than the carbon dioxide-dominated emissions documented at Mount Rainier, Mount St. Helens, and Mount Erebus.

In September 2022, a three-day field expedition brought expert cave explorers equipped with specialized self-contained breathing apparatus into the Job Glacier cave system. The hazards were considerable: darkness, technical glaciated terrain, icefall, and dangerously toxic concentrations of volcanic gases. LiDAR mapping and tacheometric surveying revealed a single interconnected system of subglacial passages with two entrances and a depth range of 59 meters, containing two distinct fumarolic areas, heated bedrock, a subglacial stream, and pools of standing water. Fumarole temperatures measured by thermal camera ranged from 28 to over 90 degrees Celsius, while the surrounding ice walls hovered between minus 3 and plus 2 degrees, a striking thermal contrast at the rock-ice boundary.

Gas measurements taken at the source were dramatic. Near the fumaroles, hydrogen sulfide exceeded 200 parts per million, sulfur dioxide exceeded 100 parts per million, carbon dioxide reached approximately 5,200 parts per million, and carbon monoxide measured about 230 parts per million. Methane was undetected. The sulfur isotope composition of the hydrogen sulfide, with a δ34S value near zero per mil, points to a deep magmatic origin for the sulfide, consistent with gases exsolving from magma at depth. Spectral analyses of yellow crystal-like deposits within the cave identified native elemental sulfur, along with ferric oxyhydroxides and alteration minerals such as goethite and illite, all hallmarks of active hydrothermal systems.

The geochemistry of cave sediments and waters told a complementary story. Sediments and water inside the cave were acidic, with pH values ranging from 3.6 to 6.0, and rich in sulfate, which ranged from 5.3 to 185.2 milligrams per liter, likely produced by the oxidation of fumarolic hydrogen sulfide. Most other major ions were below detection. Snow at the cave entrance was more acidic and sulfate-bearing than snow collected 50 meters away, which had a near-neutral pH of 7.6 and no detectable sulfate, clear evidence that fumarole exhalations are chemically transforming the surrounding snowpack. Water inside the cave appears to originate from snowmelt, as indicated by the strongly negative hydrogen and oxygen isotope values typical of meteoric precipitation.

Life was abundant and active throughout the system. Direct microscopic counts revealed between roughly 34,000 and 6.35 million cells per gram of sediment, and adenosine triphosphate measurements, a proxy for metabolic activity, were detectable in every snowmelt and water sample. The highest ATP concentration of the entire study, about 12,739 picomolar, came from a geothermally heated stream inside the cave, suggesting that flowing water provides particularly favorable conditions for metabolically active cells. The surrounding snowpack hosted spectacular blooms of pigmented snow algae, with chlorophyll a concentrations up to two orders of magnitude higher than those reported for snowpack at Mount Baker, a nearby glaciated volcano without comparable fumarolic influence at the sampling sites.

The microbial community composition set Mount Meager apart from other glacial environments. Green algae of the phylum Chlorophyta, including the genera Chlamydomonas and Chloromonas, dominated the snowpack eukaryotes, consistent with other Pacific Northwest glaciers. But the bacteria were another matter entirely. Firmicutes were the most abundant bacterial phylum across all samples, reaching 98.7 percent of reads at one fumarole-adjacent site, whereas other glacier and snowpack studies typically report abundant Sphingobacteria, Betaproteobacteria, and Alphaproteobacteria. Sulfur-cycling taxa were prominent: Acidithiobacillaceae made up 36.1 percent of reads at one cave site, and putatively thermophilic archaea of the Thermoplasmatales group A10, previously found in hot springs and acid mine drainage, were detected in the warmer cave sediments but not in the snowpack.

Shotgun metagenomic sequencing of sediment from the lower cave painted a picture of extraordinary metabolic versatility. The assembled metagenome contained complete gene pathways for three autotrophic carbon fixation strategies, the Calvin-Benson-Bassham cycle, the Wood-Ljungdahl pathway, and the Arnon-Buchanan pathway, along with complete dissimilatory sulfate reduction and sulfur oxidation via the Sox system. Notably, genes for photosystems were absent, confirming that the community relies on chemosynthesis rather than photosynthesis in the sunless depths. The researchers suggest that niche partitioning around energy availability shapes which carbon fixation pathway each organism employs, since the Wood-Ljungdahl and Arnon-Buchanan pathways require far less energy per mole of carbon fixed than the Calvin cycle. Individual genome bins revealed further specializations, including potential sulfur disproportionation, anaerobic carbon monoxide oxidation, and nitrate reduction.

Carbon isotope values added independent evidence of in-situ microbial activity. Organic matter in the sediments carried δ13C values between minus 29.0 and minus 26.1 per mil, typical of biological biomass on Earth, and dissolved organic carbon in snowmelt was even more depleted, down to minus 37 per mil, which the authors attribute to local microbial carbon transformations rather than imported soil organic matter. Together with the cell counts, ATP measurements, and functional genes, the isotope data support the conclusion that both heterotrophic and autotrophic metabolisms are actively cycling carbon in the cave sediments, driven ultimately by the chemical energy supplied by volcanic gases.

Beyond its value for understanding Earth’s cryosphere, the Mount Meager cave system offers a rare terrestrial analog for astrobiology. On Enceladus and possibly Europa, cryovolcanic plumes transport material from subsurface oceans through the icy shell and deposit it on the surface, where it could carry biomarkers or even cells from below. While cryovolcanism does not occur on Earth, glaciovolcanic fumaroles perform an analogous function, venting reduced gases and subsurface materials through ice to a photic, oxidizing surface environment. Cassini’s detection of molecular hydrogen and methane in the Enceladus plume provided evidence of seafloor hydrothermal activity, and thorough characterization of terrestrial systems like Mount Meager can help scientists develop and test the mission concepts, instruments, and operational strategies needed for future life-detection missions to the icy ocean worlds of the outer solar system.

Subject of Research: Biogeochemistry and microbiology of the sulfidic glaciovolcanic cave system on Mount Meager, British Columbia

Article Title: Biogeochemistry of the rare sulfidic glaciovolcanic cave system on Mount Meager, British Columbia, Canada

Article References: Clance, J. J., Shaffer, J. M. C., Cable, M. L., Stenner, C., Williams-Jones, G., Szynkiewicz, A., Paton, M., Graham, K., Vinnes, O., & Mikucki, J. A. (2024). Biogeochemistry of the rare sulfidic glaciovolcanic cave system on Mount Meager, British Columbia, Canada. Frontiers in Geochemistry, 2, Article 1410338. https://doi.org/10.3389/fgeoc.2024.1410338

Image Credits: AI Generated

DOI: 10.3389/fgeoc.2024.1410338

Keywords: glaciovolcanism, Mount Meager, glacier caves, fumaroles, hydrogen sulfide, chemosynthesis, microbiology, biogeochemistry, snow algae, astrobiology, Enceladus, ocean worlds

The research, published in Frontiers in Materials, addressed a persistent gap in asphalt emission science. Most previous studies relied on discrete sampling, capturing a single snapshot of fume composition at one moment in time. Yet asphalt fume emission is inherently dynamic: volatile components surge when heating begins, peak, and then decay as the most readily releasable fractions are depleted. To capture this behavior, the team built an integrated experimental system combining controlled fume generation in a sealed, thermostatically heated flask with mechanical stirring, real-time monitoring of volatile organic compounds and sulfur-containing gases, and offline collection of fumes for detailed chemical analysis by gas chromatography–mass spectrometry.

Repeatability was a central concern. The researchers standardized the thermal history of every sample, heating the asphalt at 140 degrees Celsius for four hours before dividing it into test portions, then reheating each portion for two hours before monitoring. Each test used 500 grams of asphalt, stirred at 300 revolutions per minute, with VOC concentrations recorded every 10 seconds for 90 minutes. Duplicate tests at five temperatures showed relative deviations below 10 percent during the principal response stages, well within the acceptance criterion of 20 percent, confirming that the system could reliably distinguish genuine differences between materials from experimental noise.

The team first compared four penetration-grade 90 asphalt binders from different sources, designated ZH90#, SK90#, JB90#, and GX90#, across temperatures from 120 to 200 degrees Celsius. All four showed VOC responses that increased with temperature, generally peaking before settling into a slowly varying stage. But the magnitude of the response depended strongly on the crude-oil source of the binder. At 200 degrees Celsius, the peak VOC concentration of ZH90# exceeded five times that of GX90#, even though the four binders had similar penetration and softening-point values. The finding carries a practical warning: conventional physical properties alone cannot predict the fume-emission potential of an asphalt binder, and temperature-control strategies should account for the specific source of the material rather than assuming a uniform response across all binders.

The most striking results emerged when crumb rubber entered the picture. The researchers prepared CRMA by incorporating 20 percent by weight of 40-mesh crumb rubber, derived from end-of-life tires with no desulfurization or activation pretreatment, into the ZH90# base binder. At 200 degrees Celsius, the peak VOC concentration of the modified asphalt reached 3,719.1 milligrams per cubic meter, approximately 5.5 times the 672.9 milligrams per cubic meter recorded for the base asphalt alone. The late-stage mean concentration showed a similar ratio of 5.63, and the cumulative response, calculated as the area under the concentration–time curve, was nearly five times higher. The peak also arrived earlier, at 110 seconds rather than 570 seconds, indicating that the rubber-modified binder released its volatile burden more rapidly.

Temperature proved to be the dominant amplifier. Raising the temperature of the modified asphalt from 180 to 200 degrees Celsius increased the peak VOC concentration by 253 percent, the late-stage concentration by 286 percent, and the cumulative response by 275 percent. The researchers attribute this nonlinear surge to three coupled processes: volatilization of light fractions from the base asphalt, enhanced thermal desorption of low-molecular-weight components bound within the rubber matrix, including residual monomers, processing oils, and vulcanization additives, and swelling-induced mass transfer, in which the rubber absorbs aromatic fractions from the binder, expands its interfacial contact, and opens pathways for volatile substances to migrate from the material interior into the gas phase. Notably, the response was not strictly monotonic at every temperature: the modified asphalt showed lower monitored emissions at 160 degrees Celsius than at 140 degrees Celsius, a local anomaly the team interprets as the combined effect of components released before formal monitoring began and temperature-dependent swelling that altered how light components partitioned among the binder, rubber phase, and gas phase.

Sulfur-containing gases added another dimension to the emission profile. The maximum recorded hydrogen sulfide concentration increased from 10 parts per million at 120 degrees Celsius to 31 parts per million at 200 degrees Celsius, while the cumulative H2S response rose from 265 to 1,035 parts per million·minutes over the same interval. Sulfur dioxide responses were consistently higher, with cumulative values increasing from 3,785 to 5,715 parts per million·minutes as temperature climbed from 120 to 200 degrees Celsius. At every temperature tested, the maximum recorded values for both gases occurred at the onset of formal monitoring, followed by an overall decline, suggesting that sulfur species are released most intensely during the earliest stages of sustained heating.

Gas chromatography–mass spectrometry revealed the chemical fingerprints behind these dynamic responses. Fumes from the base asphalt were dominated by petroleum-derived hydrocarbons, including heptane, octane, decane, styrene, naphthalene, and polycyclic aromatic compounds such as phenanthrene and fluoranthene. The modified asphalt fumes retained these aromatic signals but added a distinctive set of rubber-associated compounds: isoprene and its dimer dipentene, which trace to the polyisoprene structure of tire rubber; benzothiazole and methylbenzothiazole, associated with vulcanization accelerator systems; benzothiophene and dibenzothiophene, sulfur-containing heterocycles; carbon disulfide; and tetramethylthiuram disulfide, a typical sulfur-bearing rubber additive. After baseline correction, the cumulative chromatographic response of the modified asphalt fumes was 18 percent higher than that of the base asphalt, with the largest increase, 40.5 percent, concentrated in the 10-to-14-minute retention window. The researchers emphasize that no single compound serves as an independent marker of crumb-rubber origin; the diagnostic value lies in the simultaneous occurrence of this multicomponent fingerprint.

The authors are careful about what their numbers mean. The real-time concentrations are laboratory-specific sensor-equivalent values, determined by the particular reactor scale, gas-flow configuration, and instrumental calibration, intended for comparative assessment among samples and temperatures rather than direct estimation of field emissions or occupational exposure. Laboratory binder tests differ from plant-scale production in processing scale, adsorption by mineral aggregates, ventilation conditions, and thermal history, and field studies have shown that paving temperature, binder content, task, and work rate all significantly affect worker exposure. The findings therefore provide a basis for optimizing processing temperatures and designing targeted fume control, not regulatory limits.

The engineering implications are nonetheless concrete. Because emissions intensified most sharply in the 180-to-200-degree regime, the researchers recommend adopting the lowest temperature that achieves the intended dispersion, swelling, and pavement performance, minimizing high-temperature storage, recirculating heating, and repeated reheating, and using multipoint temperature measurements to prevent localized overheating near 200 degrees Celsius. Fume capture should cover the entire processing sequence, from crumb-rubber addition through mixing, swelling, transfer, and storage, with local exhaust ventilation activated before processing begins, since the highest sulfur-gas responses occurred at the onset of monitoring. Collected fumes should be treated in stages, removing particulates and condensable droplets first, then applying VOC adsorption, condensation, or oxidation according to composition, with dedicated units for H2S and SO2. And because the unresolved VOC maximum at 120 degrees Celsius showed that even lower-temperature operation does not eliminate prolonged fume release, ventilation and capture must remain active throughout both heating and holding. For a recycling technology poised to expand worldwide, the study delivers a clear message: the greenest binder is only as clean as the temperature at which it is processed.

Subject of Research: Dynamic fume emission behavior and chemical composition of crumb-rubber-modified asphalt compared with base asphalt across processing temperatures

Article Title: Characteristics of fume components and dynamic emission behavior of crumb-rubber-modified asphalt

Article References: Luo, L., Dai, J., Zhu, W., Li, C., Yu, L., Liu, Y., Li, B., & Zhang, Z. (2026). Characteristics of fume components and dynamic emission behavior of crumb-rubber-modified asphalt. Frontiers in Materials, 13, Article 1979048. https://doi.org/10.3389/fmats.2026.1979048

Image Credits: AI Generated

DOI: 10.3389/fmats.2026.1979048

Keywords: crumb-rubber-modified asphalt, asphalt fumes, volatile organic compounds, hydrogen sulfide, sulfur dioxide, gas chromatography–mass spectrometry, tire recycling, thermal desorption, emission control, pavement materials, Frontiers in Materials, dynamic emission behavior

Necroptosis is not the quiet, tidy demolition of apoptosis. It is programmed necrosis, a caspase-independent form of cell demise in which organelles swell and the plasma membrane ruptures outright, spilling inflammatory contents into the surrounding brain tissue. The pathway is driven by a necrosome complex assembled from three proteins: receptor-interacting protein kinase-1 (RIPK1), receptor-interacting protein kinase-3 (RIPK3), and mixed lineage kinase domain-like protein (MLKL). When RIPK1 and RIPK3 phosphorylate MLKL, the executioner protein migrates to the membrane and tears it apart. Because necroptosis is triggered by energy depletion, oxidative stress, and reactive oxygen species (ROS) accumulation, it is tailor-made for the conditions that prevail during reperfusion injury.

Hydrogen sulfide has long been recognized as an endogenous gaseous signaling molecule with neuroprotective, antioxidative, anti-inflammatory, and anti-apoptotic roles in the central nervous system. Sodium hydrosulfide (NaHS), a stable exogenous H2S donor, releases the gas continuously both in vivo and in vitro. Yet the extent to which H2S’s neuroprotective effects depend on regulating neuronal necroptosis remained inadequately explored, and systematic biochemical and morphological evidence linking the gas to the necroptotic signaling pathway during ischemia-reperfusion injury was scarce. The new study set out to close that gap.

In vitro, the researchers established an oxygen-glucose deprivation (OGD) model using SH-SY5Y neuronal cells to simulate ischemia-reperfusion injury. Cell viability declined in a time-dependent fashion, falling to 78.6 percent after 2 hours of OGD, 57.6 percent after 4 hours, 39.3 percent after 6 hours, and 29.0 percent after 8 hours. Alongside this decline, the necroptotic rate rose sharply, ROS overaccumulated, mitochondrial membrane potential collapsed, and the expression levels of RIPK1, RIPK3, and MLKL climbed. Pretreatment with moderate doses of NaHS significantly enhanced cell viability, mitigated ROS overproduction, restored mitochondrial membrane potential, and inhibited OGD-induced neuronal necroptosis. Necrostatin-1 (Nec-1), a specific pharmacological inhibitor of RIPK1 kinase activity, produced comparable protection, and both agents effectively suppressed activation of the RIPK1-mediated signaling pathway.

The oxidative arm of the mechanism proved equally important. Necroptosis is often associated with excessive ROS generation, and previous research has shown that necroptosis itself generates substantial ROS, which in turn stimulates further RIPK1 expression, creating a self-amplifying loop of cellular damage. In the new experiments, the potent ROS scavenger N-acetylcysteine (NAC) increased cell survival from 50.65 percent to 80.57 percent after OGD, mirroring the effect of NaHS, which raised survival to 74.30 percent. NaHS and Nec-1 both significantly reduced ROS production and reversed the OGD-induced decline in mitochondrial membrane potential, indicating that OGD escalates ROS in a concentration-dependent manner and that H2S interrupts the vicious cycle at its source.

To translate these cellular findings into a living brain, the team established a mouse model of transient middle cerebral artery occlusion followed by reperfusion (MCAO/R). Two hours of filament-induced ischemia produced severe neurological dysfunction, cerebral hypoperfusion, brain edema, extensive infarction, and neuronal ultrastructural damage. Mice treated with NaHS or Nec-1 showed significantly improved neurological deficit scores on both the modified Bederson and Zea-Longa scales by the third and sixth days after modeling. Laser speckle contrast imaging revealed that both interventions markedly increased red and yellow perfusion signals within the ipsilateral infarct core, indicating preserved microcirculatory blood flow. Brain water content dropped significantly in both treatment groups, and TTC staining showed that infarct volume fell from 38.29 percent of the hemisphere in untreated animals to 27.55 percent with NaHS and 23.82 percent with Nec-1.

Transmission electron microscopy provided striking morphological confirmation. In sham-operated mice, neuronal nuclei displayed regular contours with evenly distributed chromatin, structurally intact mitochondria with clear cristae, and well-organized endoplasmic reticulum. In the MCAO/R group, neurons exhibited extensive chromatin condensation, pronounced mitochondrial swelling with disrupted cristae, disintegrated endoplasmic reticulum, and widespread cytoplasmic vacuolization, the hallmark ultrastructural signature of necrotic cell death. Remarkably, neuronal injuries affecting nuclei, mitochondria, and endoplasmic reticulum were significantly mitigated in both the NaHS and Nec-1 groups, where organelle structural integrity was substantially restored. Western blotting confirmed that both treatments downregulated RIPK1 and RIPK3 expression in the injured cortex, demonstrating that exogenous H2S inhibited MCAO/R-induced necroptosis by suppressing the RIPK1-RIPK3 signaling pathway in vivo.

The convergence of NaHS and Nec-1 on the same molecular target is the study’s most compelling technical achievement. Because Nec-1 reduces RIPK1 kinase activity by inhibiting RIPK1 serine phosphorylation at multiple residues, the fact that NaHS produced equivalent protection suggests that H2S directly targets RIPK1 and ROS, thereby attenuating RIPK1-mediated necroptosis. This interference disrupts subsequent signaling cascades by decreasing RIPK3 phosphorylation, inhibiting MLKL activation, and impeding necrosome complex assembly, ultimately halting necroptotic cell demise. The authors note that the direct interaction between H2S and downstream molecules of RIPK1, including RIPK3 or MLKL, was not thoroughly explored, and that H2S may also exert direct inhibitory effects on calcium influx and facilitate restoration of mitochondrial oxidative stress damage, pathways warranting further exploration.

Several limitations temper the translational enthusiasm. All phenotypic and mechanistic validations were performed in cell models and animal paradigms without verification in clinical tissue samples. The in vivo data were acquired from preliminary exploratory experiments with a relatively small sample size of three animals per group, which may undermine statistical power. The lack of gene knockout validation limits the robustness of the causal mechanistic evidence. Moreover, the study adopted a preconditioning strategy, administering H2S before ischemic injury, which cannot fully recapitulate the pathological characteristics of clinical ischemic stroke. Subsequent studies will focus on post-ischemic H2S administration to better simulate clinical scenarios and improve translational relevance.

Beyond the experimental constraints, the clinical transformation of H2S-based therapy faces inherent challenges. Direct inhalation of gaseous H2S is constrained by safety hazards and poor concentration controllability, while H2S-releasing donors serve as a more feasible alternative. H2S possesses a narrow therapeutic window and potential off-target adverse effects that cannot be overlooked in clinical practice, and heterogeneous therapeutic responses among individual patients may arise from variations in genetic background, metabolic status, and comorbidities. Nevertheless, the findings provide direct in vitro and in vivo evidence that H2S plays a significant role in inhibiting RIPK1-dependent necroptosis in the pathogenesis of cerebral ischemia-reperfusion injury, offering a novel theoretical basis for the clinical management of ischemic stroke and highlighting the potential of H2S-based interventions as a promising therapeutic agent for stroke treatment.

Subject of Research: Hydrogen sulfide protects against cerebral ischemia/reperfusion injury by inhibiting RIPK1-mediated neuronal necroptosis and ROS overaccumulation.

Article Title: Exogenous hydrogen sulfide alleviates cerebral ischemia/reperfusion injury via inhibiting RIPK1-mediated neuronal necroptosis and ROS overaccumulation

Article References: Huang, C., Shang, H., Fang, Z., Zhu, L., Chen, C., & Zang, Y. (2026). Exogenous hydrogen sulfide alleviates cerebral ischemia/reperfusion injury via inhibiting RIPK1-mediated neuronal necroptosis and ROS overaccumulation. Frontiers in Molecular Biosciences, 13, Article 1968646. https://doi.org/10.3389/fmolb.2026.1968646

Image Credits: AI Generated

DOI: 10.3389/fmolb.2026.1968646

Keywords: hydrogen sulfide, stroke, necroptosis, RIPK1, ROS, cerebral ischemia, neuroprotection, Exogenous, hydrogen, sulfide, alleviates, cerebral

The biological stakes are considerable. Hydrogen sulfide is produced endogenously by three principal enzymes: cystathionine beta-synthase, known as CBS, cystathionine gamma-lyase, known as CSE or CTH, and 3-mercaptopyruvate sulfurtransferase, known as 3-MST or MPST. But production is only half of the story. Sulfide is continuously cleared by a mitochondrial oxidation pathway that begins with sulfide:quinone oxidoreductase, or SQOR, and continues through persulfide dioxygenase, ETHE1, and thiosulfate sulfurtransferase, TST, with sulfite oxidase, SUOX, finishing the job by oxidising sulfite to sulfate. Net hydrogen sulfide bioavailability therefore reflects a dynamic balance between synthesis and clearance. Assessing only one side of this equation, the authors argue, provides an incomplete and potentially misleading picture of what is actually happening in placental tissue.

That incomplete picture is precisely what the review uncovered. Of the 64 studies included, CBS was investigated in 34 and CSE/CTH in 29, mostly at the level of protein and mRNA expression, while 3-MST/MPST appeared in only seven studies. Most remarkably, not a single included study measured SQOR, ETHE1 or TST in placental tissue at either the mRNA or protein level. SUOX was reported in just two studies, both at the mRNA level. This means that the entire clearance arm of placental sulfide metabolism, the machinery that determines how much sulfide actually accumulates inside cells, remains essentially unexamined. Because reduced expression of a biosynthetic enzyme does not necessarily mean reduced sulfide signalling, conclusions drawn from synthesis alone may underestimate, overestimate or misattribute changes in hydrogen sulfide bioavailability in complicated pregnancies.

The review also exposed a heavy concentration of research interest in a single pregnancy complication. Pre-eclampsia dominated the literature, accounting for 27 of the 78 non-mutually exclusive condition assignments, compared with 12 studies of normal pregnancy and only seven on fetal growth restriction. Gestational diabetes and recurrent pregnancy loss were each represented by a single study, and preterm birth by just three. This clustering makes it difficult to know whether findings reported in pre-eclampsia apply to other placental disorders, and it leaves large areas of reproductive medicine, including premature rupture of membranes and other understudied conditions, almost entirely unmapped with respect to hydrogen sulfide biology.

Measurement itself emerged as a major methodological problem. Only 23 of the 64 studies reported sulfide concentrations, relative assay signals or hydrogen sulfide production, and they used six different analytical approaches. Methylene blue assays accounted for 18 of the 28 identified assay applications, with the remainder using lead acetate detection, fluorescent probes, sulfide-sensitive electrodes, RP-HPLC with monobromobimane derivatisation, or gas chromatography-mass spectrometry. These methods differ fundamentally in what they detect. Acidification-based methylene blue methods can release sulfide from acid-labile sulfur pools, so the resulting measurement may include sulfide that was never present as free hydrogen sulfide. Fluorescent probes generally provide relative signals rather than absolute concentrations, while substrate-supplemented incubations measure generating capacity rather than steady-state sulfide availability. Units, calibration standards and sample-processing procedures varied across studies, making direct quantitative comparison between them effectively impossible.

The consequences of this heterogeneity are visible in the conflicting results the review catalogued. Some studies reported lower placental hydrogen sulfide production in pre-eclampsia, and reduced placental sulfide was also reported after gestational cigarette-smoke exposure and maternal high-fat diet. Yet one study reported approximately two-fold higher placental hydrogen sulfide content in early-onset pre-eclampsia than in preterm controls, and another found no difference in maternal plasma sulfide between normal pregnancy and early- or late-onset pre-eclampsia using GC-MS. Differences in sample compartment, assay method, sulfide pool and reporting units prevented any pooling of these results, leaving the field without a consensus on whether sulfide is genuinely depleted in the diseased placenta.

On the therapeutic side, the review charted 85 experimental intervention applications across 38 studies, and the overall pattern was encouraging. Fast-releasing sulfide donors such as sodium hydrosulfide accounted for 26 applications, with slow-releasing donors, a mitochondria-targeted donor, organosulfur compounds, substrate supplementation, enzyme inhibition and genetic approaches making up the rest. Donor-based studies were predominantly associated with improved placental and trophoblast outcomes, including better angiogenic balance, enhanced trophoblast migration and invasion, improved mitochondrial function and reduced inflammation and cell death, while inhibition or genetic suppression of hydrogen sulfide-producing enzymes generally worsened outcomes. Notably, no clinical study has yet tested a hydrogen sulfide-modulating intervention directly in human pregnancy, so all of this evidence remains preclinical.

Yet the authors caution against reading donor studies as proof of endogenous deficiency. A sulfide measurement was reported in only 23 of the 85 intervention applications, and six of those involved maternal plasma alone. In many studies the intervention was intended to raise hydrogen sulfide availability, but the resulting change in sulfide within the relevant placental compartment was never experimentally confirmed, so interpretation rested on the expected action of the donor rather than a measured exposure. Complicating matters further, effects may occur at multiple biological compartments: in one cited example, sodium hydrosulfide showed direct cardioprotective effects in isolated chicken embryo hearts, independent of any maternal or placental influence. Without concurrent sulfide measurements, the magnitude of biological responses cannot be reliably linked to the sulfide actually delivered.

The review also highlighted a striking temporal blind spot. Human placental studies were heavily weighted toward late gestation, relying on tissue collected at delivery or near-term explants, while first-trimester evidence was limited to a small number of studies. During the first trimester the placenta develops in a relatively low-oxygen, histiotrophic environment before the maternal arterial circulation is fully established, a fundamentally different setting from the mature organ examined after birth. Findings from late-gestation tissue therefore cannot establish when hydrogen sulfide pathway alterations arose, or whether they preceded the development of placental disease, a distinction that matters enormously for identifying causes rather than consequences of pathology.

The authors conclude that placental hydrogen sulfide research has concentrated on biosynthetic enzyme expression and pharmacological modulation while leaving sulfide clearance, early gestation and standardised measurement as major gaps. Future work, they argue, should assess enzyme expression, enzyme activity, hydrogen sulfide production and oxidation capacity within the same preparation, state precisely which sulfide pool is being measured, and extend investigation beyond pre-eclampsia into gestational diabetes, recurrent pregnancy loss and preterm birth. Only then can the field resolve whether altered signalling in complicated pregnancies reflects reduced synthesis, impaired clearance, or a shift between compartments, and only then can the long-hypothesised promise of hydrogen sulfide-based therapies for placental disease be properly evaluated.

Subject of Research: Hydrogen sulfide biosynthesis and oxidation pathways in placental health and pregnancy disease

Article Title: Mapping Hydrogen Sulfide Biosynthesis and Oxidation Pathways in Placental Health and Disease: a Scoping Review

Article References: Nkuba, A., Bushell, C. J., Rivera, L. R., Aston-Mourney, K., Mahmood, M. Q., & McNeill, B. A. (2026). Mapping Hydrogen Sulfide Biosynthesis and Oxidation Pathways in Placental Health and Disease: a Scoping Review. Reproductive Sciences. https://doi.org/10.1007/s43032-026-02236-y

Image Credits: AI Generated

DOI: 10.1007/s43032-026-02236-y

Keywords: hydrogen sulfide, placenta, pre-eclampsia, trophoblast, CBS, CSE, 3-MST, sulfide oxidation, SQOR, fetal growth restriction, scoping review, sulfide measurement

The core difficulty the researchers confronted is one that plagues many fast-moving fields: inconsistent reporting. Even for the same target gas, studies may use different operating temperatures, humidity conditions, baseline stabilization times, and gas-delivery protocols, all of which shift the measured response. Sensitivity itself is defined in at least four different ways across the literature, some based on the ratio of resistance in air to resistance under gas exposure, others on fractional changes relative to different baselines. Some sensors report resistance changes, others current modulation, frequency shifts, or even capacitance-voltage characteristics. Headline numbers, the authors argue, simply cannot be compared without first accounting for this measurement context.

To build a foundation for comparison, the team assembled a curated dataset of 91 literature-reported gas sensors spanning five target gases, drawn primarily from comprehensive MEMS-focused review literature. Microelectromechanical systems technology has enabled compact sensors that integrate sensing layers, electrodes, and microheaters on a single chip, supporting low-power operation and scalable fabrication. The compiled entries cover a remarkable breadth of materials: metal oxides, palladium alloys, metal-organic frameworks, carbon-based materials, sulfur-based materials, polymers, and hybrid composites, fabricated through sputtering, sol-gel deposition, hydrothermal growth, and atomic-layer deposition.

Standardizing this heterogeneous data required careful preprocessing. Material categories were converted into binary indicator variables, temperature and detection ranges were split into lower and upper bounds, and textual entries such as room temperature were assigned a conventional value of 25 degrees Celsius. Critically, the four resistance-based sensitivity formulations encountered in the literature were converted into a single canonical representation, R3, which expresses the fractional change in resistance relative to the air baseline. The authors were careful to apply this standardization only to resistance-based measurements, refusing to equate fundamentally different transduction mechanisms. For ammonia sensors, whose reported responses span resistance, potential, frequency, and counts, the physical signal type was instead encoded as separate categorical variables.

With the data harmonized, the researchers applied principal component analysis independently to each gas dataset. PCA transforms correlated variables into a smaller set of orthogonal components ordered by explained variance, revealing which factors dominate the differences between sensors. Because the method is sensitive to scale, all features were first standardized to zero mean and unit variance, preventing variables with large numerical ranges from dominating the results. The resulting components served both for interpretation through their loadings and as a two-dimensional embedding for the subsequent clustering step.

For clustering, the team chose DBSCAN, a density-based algorithm that groups points whose neighborhoods overlap while explicitly labeling isolated points as noise. This choice proved important: DBSCAN requires no advance specification of the number of clusters, makes no assumption about cluster shape, and naturally identifies outliers rather than forcing every observation into a group. The neighborhood radius was selected per gas using a data-driven k-nearest-neighbor elbow heuristic, and stability was verified through leave-one-out analysis, repeated subsampling, and an independent HDBSCAN run that reproduced the hydrogen partition exactly.

The results are striking in their consistency. Across hydrogen, carbon monoxide, nitrogen dioxide, and hydrogen sulfide sensors, material class and operating temperature emerged as the dominant drivers of variance, with metal-oxide and metal-based sensors operating predominantly at elevated temperatures while polymer and carbon-based sensors clustered near room temperature. Carbon monoxide sensors showed the most structured feature space of all, with the first two components capturing 74.15 percent of total variance and a sharp, symmetric split between high-temperature metal-oxide regimes and room-temperature polymer designs. Hydrogen sulfide sensors displayed the strongest temperature-material coupling, with operating temperature range acting as an unusually consistent predictor of material class.

Ammonia told a different story entirely. With only 37.81 percent of variance captured by the first two components, ammonia sensors proved the most heterogeneous group, and signal transduction modality, whether resistance, frequency, or counts, became a stronger differentiator than material composition alone. This finding underscores that sensor selection for ammonia is inherently application-specific, depending on an interplay of material, operating conditions, and measurement strategy. Meanwhile, the outliers flagged by the framework in every dataset turned out to be physically meaningful edge cases, such as sensors with exceptionally wide detection ranges, ultralow parts-per-billion targets, or atypical transduction modalities, rather than data-processing artifacts.

The authors are candid about limitations: the dataset derives primarily from two review articles, per-gas sample sizes remain modest, and response and recovery times were excluded because they were jointly available for only about half to three-quarters of sensors and reported at inconsistent test concentrations. PCA captures only linear relationships, and DBSCAN remains sensitive to density assumptions. Even so, the work establishes a reproducible template for cross-study comparison, and the team proposes extending it with systematic primary-literature screening, nonlinear dimensionality-reduction methods such as t-SNE and UMAP, and explicit links to physical design variables like nanostructure geometry and catalytic decoration. If successful, such extensions could move the field from describing sensor performance toward predicting and designing it, a shift with significant implications for safety monitoring in the hydrogen economy and beyond.

Subject of Research: Data-driven multivariate analysis of MEMS gas sensor performance across five target gases

Article Title: Data-driven framework for analyzing gas sensor performance using principal component analysis and clustering

Article References: Abir, A., Metwaly, M., & Murshid, N. (2026). Data-driven framework for analyzing gas sensor performance using principal component analysis and clustering. Results in Chemistry, 31, Article 103948. https://doi.org/10.1016/j.rechem.2026.103948

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103948

Keywords: gas sensors, principal component analysis, DBSCAN clustering, MEMS, hydrogen sensing, carbon monoxide, nitrogen dioxide, hydrogen sulfide, ammonia, metal oxides, sensitivity standardization, machine learning

A research team led by Professor Qian Peiyuan, Chair Professor of the Department of Ocean Science at The Hong Kong University of Science and Technology, in collaboration with international partners, has now delivered some of the most direct evidence to date. Working at the Haima cold seep, the team showed that metabolic flexibility in bacterial symbionts, combined with the host clam’s finely regulated management of its bacterial population, mutually sustains the animal’s energy stability. The findings, published in the leading international journal Science Advances under the title “In situ evidence of tiered adaptations buffering a chemosynthetic clam holobiont against environmental sulfide fluctuations,” reveal a tiered adaptation strategy that helps explain how cold seep ecosystems remain resilient when energy supplies fluctuate.

The research was conducted in collaboration with the Southern Marine Science and Engineering Guangdong Laboratory in Guangzhou, Ocean University of China, the Institute of Oceanology of the Chinese Academy of Sciences, and the University of Calgary in Canada. It also represents an important outcome within the framework of two UN Decade of Ocean Science programmes, CliMetS and MOCSI. The study’s co-corresponding authors include Professor Qian, Professor Sun Jin of Ocean University of China, and Professor Casey Hubert of the University of Calgary, while the co-first authors are Dr. Lan Yi, Dr. Yan Guoyong, and Dr. Wang Hao.

What sets this study apart is its experimental design. Direct evidence of how deep-sea symbioses respond to environmental change has long been lacking, largely because most studies rely on specimens collected and then analyzed on the surface, a process that can distort the very molecular signals researchers hope to capture. The Haima cold seep offered a solution. Because it comprises seep sites at different developmental stages, it functions as a natural laboratory in which biological responses to environmental change can be observed across a gradient of conditions.

The team focused on Archivesica marissinica, a dominant species of deep-sea clam at Haima, and its sulfur-oxidizing bacterial symbionts. Using deep-sea in situ transplant experiments combined with in situ sample fixation, the researchers moved clams from their native sediments into transplantation cages positioned approximately half a meter above the seafloor. Suspended in the water column, the clams could no longer access the sulfide-rich sediment below, simulating a decline in hydrogen sulfide availability and the reduced energy and nutrient acquisition that follows. Two sites were chosen to represent different degrees of stress: HM-2, where sulfide limitation was severe, and HM-3, where the limitation was relatively moderate.

Back on shore, the team deployed an unusually comprehensive analytical arsenal, integrating metagenomics, transcriptomics, proteomics, quantitative PCR, in situ hybridization, transmission electron microscopy, and protein structure prediction. Together, these approaches illuminated a tiered adaptation strategy operating across three levels: the metabolism of the symbionts themselves, the host’s regulation of the symbiosis, and the transport of resources between the two partners.

The first line of defense proved to be metabolic reprogramming inside the bacterial symbionts. When hydrogen sulfide became limiting, transcriptomic and proteomic analyses showed that pathways involved in sulfide oxidation, including genes such as dsrAB, aprAB, and sat, were suppressed. At the same time, the soxXYZ gene cluster, which is associated with thiosulfate oxidation, was upregulated. In practical terms, this means that when hydrogen sulfide grows scarce, the symbionts can adjust their sulfur-oxidation strategies and potentially enhance their capacity to exploit thiosulfate, an alternative sulfur compound, thereby maintaining energy metabolism and carbon fixation. This metabolic plasticity appears to be the holobiont’s initial buffer against short-term sulfide limitation, buying time before more drastic measures become necessary.

The second tier involves the host’s management of its bacterial population, and here the response changed with the severity of the stress. Under the moderate sulfide limitation at HM-3, symbiont abundance remained stable, and the researchers observed that pathways associated with endosomal maturation and endosome-lysosome fusion in the host were suppressed. This suggests the clam reduces intracellular degradation and turnover of its bacterial partners, effectively choosing to preserve the symbiosis when resources tighten but have not yet collapsed. Under the severe limitation at HM-2, however, the picture shifted markedly. Symbiont abundance decreased significantly, and transmission electron microscopy revealed lysosomes digesting the symbionts. In other words, when the resource crisis becomes acute, the host appears to increase symbiont turnover, consuming its bacterial partners to access their nutrients as a means of survival.

The third tier centers on the clam’s own gill tissue, which possesses a strong sulfur-metabolic capacity of its own. The gills highly express key enzymes such as thiosulfate sulfurtransferase, or TST, which participates in converting toxic hydrogen sulfide into thiosulfate. That product is precisely the compound the bacterial symbionts can oxidize, as indicated by the upregulation of the soxXYZ gene cluster. This creates a potential metabolic synergy: the host’s detoxification of a poison generates an energy substrate that its symbionts can use. It is an elegant example of metabolic complementarity under resource-limited conditions, in which a waste-management problem becomes a fuel supply.

The team also investigated the role of the clam’s hemoglobins in gas transport, adding a molecular dimension to a long-standing question about vesicomyid clams. The two hemoglobin subunits, Hb1 and Hb2, are primarily localized in blood cells and are highly expressed in the foot and gill tissues. Both protein structural prediction and molecular docking results revealed that the hemoglobin complex exhibits a slightly higher binding affinity for hydrosulfide than for oxygen. This suggests the complex may mediate the binding and transport of both hydrogen sulfide and oxygen through the animal’s body, offering new molecular insight into how these clams shuttle the raw materials of chemosynthesis between their environment and their symbionts.

Professor Qian, co-corresponding author of the study, summarized the significance of the work: “Taken together, we believe that Archivesica marissinica and its symbionts form a multi-layered, tiered adaptation strategy. This enables the deep-sea chemosynthetic holobiont to maintain normal functions and survive while adjusting resource allocation according to the severity of environmental stress.” He added that the in situ experimental framework established by the research provides a new approach for investigating the authentic molecular responses of organisms inhabiting extreme deep-sea environments to natural environmental changes, and that it offers new scientific evidence for understanding how global deep-sea cold seep ecosystems respond to environmental change while maintaining ecological functions and biodiversity.

The broader implications extend well beyond a single clam species. Cold seeps and hydrothermal vents are increasingly recognized as sentinels of deep-ocean health, and understanding how their resident holobionts, the integrated units of host and symbiont, buffer themselves against fluctuating energy supplies is essential for predicting how these ecosystems will fare as ocean conditions change. By demonstrating that adaptation operates in tiers, first through symbiont metabolic flexibility, then through graded host regulation of symbiont populations, and finally through resource transport and detoxification pathways, the study provides a conceptual framework that can be tested in other chemosynthetic systems worldwide. It also validates in situ transplantation with in situ fixation as a methodological gold standard for capturing genuine molecular responses in environments where surface analysis simply will not do. As exploration of the deep ocean accelerates, such tiered strategies may prove to be a common blueprint for life at the edges of habitability, where energy is precious, unpredictable, and worth defending at every level of biological organization.

Subject of Research: Tiered adaptations of a chemosynthetic clam holobiont to sulfide fluctuations at a deep-sea cold seep

Article Title: HKUST researchers reveal a tiered adaptation strategy in deep-sea chemosynthetic symbiosis

Article References: HKUST researchers reveal a tiered adaptation strategy in deep-sea chemosynthetic symbiosis. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: deep-sea cold seep, chemosynthetic symbiosis, hydrogen sulfide, Archivesica marissinica, sulfur-oxidizing bacteria, in situ transplantation, metagenomics, transcriptomics, proteomics, hemoglobin, Haima cold seep, Science Advances

The core challenge the researchers set out to address is the asymmetry between the two substrates. Sewage sludge is a complex matrix in which much of the organic material is locked inside microbial cells and wrapped in extracellular polymeric substances, making hydrolysis the rate-limiting step of the entire digestion chain. Food waste, by contrast, is rich in readily fermentable carbohydrates that acidogenic bacteria convert into volatile fatty acids almost immediately. When the two are co-digested without intervention, the food waste acidifies rapidly while the sludge has barely begun to release its own organic content, and the resulting acid load can suppress or even collapse the methanogenic community. Pretreatment strategies have therefore become a major focus of research, with the goal of pre-disintegrating the sludge and buffering the early acidification phase before the mixture ever reaches the digester.

The pretreatment tested by the team combines two reagents with complementary chemistry. Nano zero-valent iron, or nZVI, consists of iron particles at the nanometer scale that act as strong electron donors and can promote the disintegration of sludge flocs and the disruption of cell membranes, releasing soluble organic matter that hydrolytic enzymes and fermenters can then access. Sodium percarbonate, or SPC, is a solid source of hydrogen peroxide that decomposes to release reactive oxygen species capable of oxidizing recalcitrant sludge structures, while its carbonate by-product simultaneously raises the alkalinity of the mixture. The combination is attractive from a practical standpoint because both reagents are relatively inexpensive, easy to dose, and free of the heavy-metal contamination concerns associated with some other advanced oxidation catalysts.

The quantitative results reported in the study are striking. After the nZVI/SPC pretreatment, the initial soluble chemical oxygen demand of the substrate mixture reached 22,483.6 milligrams per liter, compared with only 8,493.7 milligrams per liter in the untreated control. Soluble chemical oxygen demand is a standard proxy for how much organic material has been transferred from the particulate phase into the dissolved phase where microbes can consume it, so a nearly threefold increase signals a dramatic acceleration of substrate disintegration. The researchers also observed markedly higher release of soluble proteins and polysaccharides, the two dominant classes of organic macromolecules in sludge, confirming that the pretreatment had effectively cracked open the cellular and polymeric barriers that normally shield this material from digestion.

The downstream consequences for methane production were equally impressive. The cumulative methane yield in the pretreated co-digestion reached 412.5 milliliters per gram of volatile solids, a figure 55.2 percent higher than the control. The maximum methane production rate climbed to 48.6 milliliters per gram of volatile solids per day, and the lag phase, the initial period during which the microbial community acclimates before gas production accelerates, shortened to just 0.52 days. In anaerobic digestion engineering, a short lag phase is highly valuable because it indicates that the microbial consortium can begin productive work almost immediately, which translates into shorter hydraulic residence times and smaller, cheaper reactors for the same throughput of waste.

Perhaps the most technically significant finding concerns process stability during the acidification surge. Volatile fatty acids in the pretreated reactors peaked at 8,124.6 milligrams per liter on day seven, a concentration that in many co-digestion systems would be associated with severe acid stress and methane inhibition. Yet the pH in the reactors remained between 6.99 and 7.41 throughout, comfortably within the optimal window for methanogens. The authors attribute this resilience to effective buffering by carbonate species derived from the sodium percarbonate, which neutralize the acid wave as it forms. In effect, the pretreatment allows the system to accumulate a large pool of volatile fatty acids, which are the direct precursors of methane, without ever crossing the pH threshold at which those intermediates become toxic to the archaea that convert them into biogas.

Biogas quality also improved in ways that matter for real-world deployment. The maximum methane content of the produced gas reached 71.2 percent, well above the roughly 50 to 65 percent typical of conventional digesters, which reduces the burden of downstream biogas upgrading. At the same time, the peak hydrogen sulfide concentration decreased by 49.6 percent. Hydrogen sulfide is a corrosive and toxic contaminant that must be scrubbed from biogas before it can be used in engines or fuel cells, and iron species are known to bind sulfide as insoluble iron sulfide. The nZVI in the pretreatment therefore appears to deliver a double benefit: it accelerates the digestion chemistry while simultaneously polishing the gas stream at its source.

Microbial community analysis provided mechanistic depth to these performance gains. The pretreated reactors showed enrichment of hydrolytic and syntrophic bacteria, including members of the genera Clostridium, Syntrophomonas, and Syntrophobacter. Clostridium species are prolific fermenters that break down sugars, proteins, and other polymers into volatile fatty acids and alcohols, while Syntrophomonas and Syntrophobacter specialize in the energetically demanding oxidation of longer-chain fatty acids and propionate, reactions that only proceed when paired with hydrogen-scavenging methanogens. On the archaeal side, the community was enriched in Methanosaeta and Methanobacterium, representing the acetoclastic and hydrogenotrophic methanogenic pathways respectively. This combination indicates that the pretreatment cultivated a tightly coupled food web in which every intermediate, from complex polymers down to acetate and hydrogen, had a dedicated microbial specialist waiting to consume it.

The broader significance of the work lies in its integration of three historically separate concerns: substrate availability, acid-base management, and microbial ecology. Many pretreatment studies have focused solely on increasing solubilization, only to find that the extra soluble material simply worsens acidification. By pairing an oxidative disintegration agent with an alkalinity source in a single step, the nZVI/SPC approach addresses both sides of the problem at once, and the microbial data confirm that the resulting environment favors the exact organisms needed to convert the released organics into methane. The study was supported by the Natural Science Foundation of Shandong Province and the China Postdoctoral Science Foundation, and the authors suggest that the strategy offers a feasible pathway for efficient resource recovery from multiple organic waste streams simultaneously.

For wastewater treatment plants and biogas operators, the findings point toward a relatively low-barrier upgrade path. Both nZVI and sodium percarbonate can be dosed as solids or slurries into existing pretreatment tanks, and the improved buffering could reduce the need for external alkalinity addition, which is a recurring operating cost in food waste co-digestion. The higher methane content and lower hydrogen sulfide burden further cut downstream gas-cleaning expenses. As cities worldwide seek to divert organic waste from landfills and squeeze more energy from their wastewater infrastructure, pretreatments of this kind may prove to be among the most cost-effective levers available, turning two problematic waste streams into a cleaner, richer source of renewable fuel.

Subject of Research: Nano zero-valent iron and sodium percarbonate pretreatment to enhance anaerobic co-digestion of sewage sludge and food waste

Article Title: New insights into nZVI/SPC pretreatment for enhanced anaerobic co-digestion of sewage sludge and food waste: substrate disintegration, acidification buffering and microbial responses

Article References: Kong, Y., Zhao, J., & Liu, J. (2026). New insights into nZVI/SPC pretreatment for enhanced anaerobic co-digestion of sewage sludge and food waste: substrate disintegration, acidification buffering and microbial responses. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38291-w

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38291-w

Keywords: anaerobic co-digestion, sewage sludge, food waste, nano zero-valent iron, sodium percarbonate, methane production, biogas, volatile fatty acids, acidification buffering, microbial community, hydrogen sulfide, waste-to-energy

The research, led by Sheng-Nan Hou and corresponding author Hui Zhu of the Northeast Institute of Geography and Agroecology at the Chinese Academy of Sciences, together with colleagues from Fujian Normal University and Nanjing Normal University, set out to answer a deceptively simple question. What happens to hydrogen sulfide emissions in flooded rice paddies when green manure is incorporated at different rates, and how do those emissions connect to the microbial machinery of the sulfur cycle and to the final harvest? The answer, it turns out, is a story of thresholds, trade-offs, and a delicate microbial balance that farmers ignore at their peril.

The team designed a mesocosm experiment with four treatments representing a gradient of green manure inputs: a control with no incorporation, and three levels of 15,000, 30,000, and 45,000 kilograms per hectare. Mesocosms, essentially contained experimental ecosystems, allowed the researchers to track gas emissions, soil chemistry, plant performance, and microbial communities under controlled conditions that mimic real paddy environments. This scale of experimentation sits comfortably between laboratory incubations and full field trials, giving the results a robustness that smaller studies often lack.

The headline finding is stark. Cumulative hydrogen sulfide emissions rose in lockstep with the amount of green manure incorporated. Compared with the control, the low, medium, and high application rates produced 2.39-fold, 7.10-fold, and 8.75-fold increases in cumulative emissions, respectively. In other words, tripling the green manure input from the low to the high rate more than tripled the gas released. The timing of these emissions followed a clear and predictable pattern: hydrogen sulfide release peaked within the first 30 days after incorporation, when fresh organic matter was decomposing most rapidly, then declined steadily and essentially ceased after about 55 days.

Why does adding plant biomass to a waterlogged soil generate this toxic gas? The mechanism lies in the biology of sulfate-reducing bacteria, a group of microorganisms that thrive in the oxygen-starved conditions of flooded paddies. These bacteria respire sulfate rather than oxygen, converting it to sulfide as a metabolic byproduct. Fresh green manure delivers a surge of easily degradable carbon and nutrients into the soil, and the study found that this influx promoted the accumulation of soil nutrients including total nitrogen, total phosphorus, and total organic carbon. Those enriched conditions, in turn, enhanced the abundance of key sulfate-reducing bacteria and boosted the abundance of functional genes known as cysD and cysN, which are involved in sulfur assimilation and metabolism. More microbial capacity for sulfur processing meant more hydrogen sulfide escaping into the atmosphere.

The consequences for the rice crop were equally striking, and they reveal a Goldilocks dynamic. The low green manure rate of 15,000 kilograms per hectare enhanced rice yield by 6.02 percent compared with the control, delivering exactly the kind of benefit that has made green manuring popular. But the medium rate reduced yield by 12.25 percent, and the high rate was catastrophic, cutting yields by 42.59 percent. The pattern suggests that at moderate to high inputs, hydrogen sulfide toxicity and associated soil conditions overwhelm any nutritional benefit the added biomass provides. Hydrogen sulfide is well known to interfere with root respiration and nutrient uptake in plants, and previous work by some of the same researchers has examined the physiological mechanisms and recovery thresholds of rice plants under hydrogen sulfide stress.

What makes this study particularly valuable is that it connects the dots across multiple levels of the system simultaneously. Rather than measuring emissions in isolation, the researchers linked the gas fluxes to soil nutrient accumulation, to shifts in sulfur-cycling microbial communities, to the abundance of specific functional genes, and finally to the agronomic outcome that matters most to farmers: the size of the harvest. This chain of evidence, from organic input to nutrient enrichment to microbial proliferation to gene expression to gas emission to yield loss, provides a mechanistic narrative that few studies in this field have achieved. It transforms what could have been a simple observational correlation into a causal explanation grounded in microbial ecology.

The implications for agricultural practice are immediate and geographically specific. The authors conclude that the 15,000 kilograms per hectare treatment achieved the most favorable combination of rice yield and soil fertility performance under their mesocosm conditions, offering concrete guidance for agronomic practices in Northeast China, where the research group is based. The message is not that green manure should be abandoned, but that its application rate matters enormously. Moderate incorporation appears to hit the sweet spot, improving fertility and boosting yields without triggering the microbial sulfur cascade that produces harmful emissions at higher doses. Excessive application, by contrast, risks both environmental harm and economic loss.

Beyond the immediate agronomic recommendations, the findings open a broader window onto an underexplored dimension of agricultural greenhouse and trace gas emissions. Hydrogen sulfide from managed ecosystems has received far less attention than carbon dioxide, methane, or nitrous oxide, yet it affects plant health, contributes to odor problems, and participates in atmospheric sulfur chemistry. Related research has documented biogenic hydrogen sulfide emissions from mangrove forests and linked eutrophication in lake sediments to increased sulfur biotransformation and gas release. The new study extends this picture to one of the world’s most important cropping systems, suggesting that as organic amendments become more prevalent in sustainable agriculture, sulfur gas dynamics deserve a place alongside carbon and nitrogen in emissions accounting.

There are also important caveats and directions for future work. The experiment was conducted at mesocosm scale, and while this provides strong internal validity, field-scale confirmation across seasons, soil types, and climates will be needed to refine application thresholds for different regions. The study was supported by the National Natural Science Foundation of China, and the authors note that data will be made available on request. Nonetheless, the core insight stands: the microbial sulfur cycle in paddy soils is highly sensitive to the amount of organic carbon farmers add, and the functional genes that track this sensitivity offer a potential molecular indicator for managing green manure intelligently. As agriculture worldwide pivots toward organic and regenerative practices, this research serves as a timely reminder that sustainability is not simply a matter of adding more nature to the field. It is a matter of dose, timing, and understanding the invisible microbial economies that convert what we bury in the soil into what we breathe from it. Getting that balance right could mean the difference between a greener harvest and a stinking, sulfurous failure.

Subject of Research: Hydrogen sulfide emissions from paddy soils under varying green manure incorporation rates and their effects on rice yield

Article Title: Mechanistic insights into hydrogen sulfide emissions in paddy soils under green manure incorporation and their effects on rice yield

Article References: Hou, S.-N., Jin, X.-L., Cui, H., Sun, Z.-G., Shi, Z.-X., & Zhu, H. (2026). Mechanistic insights into hydrogen sulfide emissions in paddy soils under green manure incorporation and their effects on rice yield. Plant and Soil. https://doi.org/10.1007/s11104-026-09148-5

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09148-5

Keywords: green manure, hydrogen sulfide, paddy soil, rice yield, sulfate-reducing bacteria, soil microbiology, sulfur cycle, cysD, cysN, soil fertility, sustainable agriculture, Northeast China