The phyllosphere, as the leaf environment is called, is a notoriously difficult place to make a living. It is exposed to ultraviolet radiation, fluctuating humidity, temperature swings and scarce nutrients, and it changes dramatically with the seasons. Yet despite these pressures, leaf surfaces host complex communities of bacteria, fungi, oomycetes and other eukaryotes that influence plant health, disease resistance and even ecosystem function. Understanding which interactions hold these communities together has been a long-standing puzzle, because most studies rely on computational predictions of who interacts with whom rather than direct experimental proof of the underlying mechanisms.

To crack the problem, the researchers launched a continental-scale field survey, collecting 347 wild Arabidopsis plants from 15 natural populations spanning Spain, France, Germany and Sweden. They sequenced bacterial, fungal, oomycete and broader eukaryotic marker genes from both whole-leaf samples and surface-sterilized endophytic samples, building a multikingdom picture of who lives where. Network analysis of the resulting data revealed that certain taxa, so-called hub microbes, occupied disproportionately central positions in the microbial community. Among the most prominent were the oomycete genus Albugo and the basidiomycete yeast Dioszegia, both of which scored highly on measures of closeness and betweenness centrality, indicating that they act as connective tissue within the leaf microbiome.

Albugo laibachii is an obligate biotrophic pathogen, meaning it can only survive on living host tissue. Such pathogens typically lose essential metabolic pathways during evolution because they can steal the missing nutrients from their hosts. Albugo’s genome, for example, lacks the entire pathway for making thiamine. But there is a catch: during the earliest stages of infection, before the pathogen has penetrated the plant, the leaf surface offers almost no resources. The researchers hypothesized that other leaf-dwelling microbes might be filling this gap, and that a positive interaction between Albugo and a co-occurring microbe could explain how the pathogen manages to establish itself in nature.

Testing this idea required moving from correlation to causation. The team adapted a gnotobiotic system in which sterile Arabidopsis seedlings are grown in plates and inoculated with defined microbes, allowing them to measure how individual strains affect Albugo colonization. Of twelve candidate interactors predicted from the network analysis, most either inhibited the pathogen or had no effect. One result was particularly instructive: two strains of the yeast Leucosporidium, predicted to interact positively with Albugo, actually suppressed infection, a reminder that computational associations do not always translate into direct functional outcomes. But one strain, a Dioszegia hungarica isolate designated EY, consistently and strongly promoted Albugo infection, exactly as the network had predicted.

The molecular culprit turned out to be a gene called DhPER1, which encodes a membrane permease for thiamine. Comparing the genomes of the Albugo-promoting EY strain and a non-promoting strain from Portugal, the researchers found that DhPER1 carried the highest density of single-nucleotide polymorphisms among all thiamine-related genes, and that its expression was more than twentyfold higher in EY than in the non-promoting strain. Using a newly developed CRISPR-based transformation system for Dioszegia, they knocked out DhPER1 in the EY strain and found that the mutant lost its ability to promote Albugo infection. Complementing the mutant with the EY version of the gene restored the phenotype, confirming that this single permease is the key to the interaction.

Enzyme-linked immunosorbent assays showed that strains expressing DhPER1 secreted thiamine into their surroundings, and adding purified thiamine to the gnotobiotic system boosted Albugo infection by up to 500 percent at low concentrations. Under the microscope, the researchers observed something remarkable: Albugo zoospores, the motile spores that initiate infection, actively swam toward Dioszegia EY cells rather than drifting freely in water, suggesting that the yeast both attracts and feeds the pathogen. Transcriptomic analysis two days after infection revealed that Albugo’s overall gene expression tripled in the presence of the EY strain, with 316 genes upregulated, many involved in metabolism and membrane transport, indicating that the yeast jump-starts the pathogen’s metabolic machinery during the critical early phase of colonization.

Evolutionary analyses added a deeper layer to the story. The DhPER1 gene shows signatures of strong purifying selection in Dioszegia, with a ratio of nonsynonymous to synonymous substitutions among the most conserved of all genes, and the RELAX algorithm revealed intensified selection specifically along the D. hungarica lineage. The EY strain also carries more than twice as many tRNA genes as other D. hungarica strains, and its thiamine-related genes show significantly higher predicted translation efficiency, suggesting that natural selection has optimized the yeast’s protein-production machinery to support the cross-feeding lifestyle. These findings echo the Black Queen Hypothesis, which proposes that leaky production of costly public goods drives stable metabolic dependencies between microbes.

What does the yeast get out of the deal? In long-term co-cultivation experiments lasting 32 days, roughly the span of Arabidopsis’s vegetative growth, Dioszegia populations gradually died out on non-sterile plants when Albugo was absent, overwhelmed by the native microbiome. But when Albugo was present, the yeast populations were rescued, increasing more than a hundredfold, and strains expressing DhPER1 fared significantly better than those without it. The benefit appears to be indirect: Albugo, known from earlier work to suppress plant immunity and inhibit certain competitors, effectively engineers the leaf environment, sheltering its metabolic partner from competitive exclusion. The result is an asymmetric mutualism in which the yeast supplies a vitamin and the pathogen supplies a niche.

The implications reach well beyond Arabidopsis. Vitamin auxotrophy is widespread among bacteria in oceans, soils and the human gut, and obligate plant pathogens such as downy mildews, rusts and arbuscular mycorrhizal fungi all depend on nutrients they cannot make themselves. If the colonization of such organisms depends on nutrient supplies from the microbiome rather than solely from the host, as this study suggests, then manipulating microbial nutrient flows could become a powerful tool. Researchers envision strategies that either starve harmful obligate pathogens by disrupting their microbial supply lines or bolster beneficial symbionts by engineering cross-feeding partners, opening a new frontier in microbiome engineering for agriculture and ecosystem management.

Subject of Research: Thiamine cross-feeding between a leaf yeast and an oomycete pathogen in the Arabidopsis phyllosphere microbiome

Article Title: Thiamine cross-feeding drives microbial coexistence in the leaf microbiome

Article References: Hu, Y., Bode, J., Gómez-Pérez, D., Guerreiro, M. A., Mari, A., Wang, K., Niemann, S., Mahmoudi, M., Kemen, A., Duran, P., Wacker, O., Straub, D., Nahnsen, S., Schwessinger, B., Roux, F., Alonso-Blanco, C., Ågren, J., Hacquard, S., Stukenbrock, E. H., & Kemen, E. (2026). Thiamine cross-feeding drives microbial coexistence in the leaf microbiome. Nature Microbiology. https://doi.org/10.1038/s41564-026-02499-w

Image Credits: AI Generated

DOI: 10.1038/s41564-026-02499-w

Keywords: thiamine, cross-feeding, phyllosphere, microbiome, Arabidopsis thaliana, Albugo laibachii, Dioszegia hungarica, mutualism, keystone taxa, oomycete, plant pathology, microbial ecology

The research, published in Scientific Reports and funded by the Great Lakes Fishery Commission, was conducted by scientists from SUNY Brockport, the University of Vermont, and Oregon State University. It is the first study to examine whether fish embryos can acquire thiamine naturally in their wild incubation environment. Led by Matthew Futia of the University of Vermont’s Rubenstein Ecosystem Science Laboratory, in collaboration with the Rinchard Lab at SUNY Brockport, the team chose Lake Champlain as its experimental arena because thiamine deficiency has already been documented in stocked populations of lake trout and Atlantic salmon there, and the lake’s spawning sites are well studied.

The disorder at the center of the work is Thiamine Deficiency Complex, or TDC, a syndrome caused by insufficient vitamin B1. Thiamine is an essential cofactor in carbohydrate metabolism and neural function, and fish cannot synthesize it in useful amounts; it must be obtained from diet or the surrounding environment. In salmonines, TDC is typically observed in hatcheries that rear eggs collected from wild adults, where it produces severe behavioral and neurological abnormalities and extremely high mortality in newly hatched fish. Hatchery staff can mitigate the effects with thiamine baths or injections, but until now, essentially everything scientists knew about TDC-related mortality came from those controlled settings.

That hatchery-centric knowledge base left a glaring gap. Eggs of lake trout incubate in the wild for more than five months before haking, resting in the interstices of rocky spawning reefs where water flows continuously around them. Because thiamine is potentially highly available dissolved in water, the researchers reasoned that embryos might be absorbing the vitamin from their environment throughout that long incubation period, something no laboratory rearing protocol had ever replicated or measured.

To test the idea, the team fertilized lake trout eggs from Lake Champlain and split them between two very different fates. One portion was deployed in the lake itself, placed in egg incubation bags on natural spawning substrate, while the paired portion was reared under controlled laboratory conditions. The researchers then measured thiamine concentrations at four developmental stages in both groups, and separately analyzed the lake water to determine how much thiamine was actually available in the embryos’ surroundings.

The results were striking. Lake-reared embryos accumulated substantial amounts of thiamine as development proceeded, showing significant increases in thiamine concentrations at the time of hatching and in the weeks that followed. Their lab-reared siblings, incubated in the same water source but under controlled conditions, showed no increase at all. The contrast between the two groups demonstrates that something about the natural environment, likely the continuous exchange of lake water across the egg membranes, allows embryos to take up the vitamin in quantities that artificial rearing does not provide.

The team also detected thiamine precursors and byproducts in Lake Champlain, adding a biochemical dimension to the findings. Together, the measurements indicate that developing embryos may be able to take up sufficient concentrations of thiamine during their months in the substrate to offset problems that would otherwise arise from thiamine deficiency. In other words, the wild may be quietly doing for lake trout embryos what hatcheries must accomplish with vitamin treatments.

Futia emphasized how much this changes the interpretive frame. Prior to this study, practically everything known about the effects of TDC on newly hatched fish was based on laboratory and hatchery work, he noted, and the findings suggest that what occurs in natural environments may actually be quite different, and thankfully in a good way for the fish. That distinction matters enormously for conservation planning, because assessments of TDC risk have so far been extrapolated from hatchery observations that may not reflect what wild embryos actually experience on a spawning reef.

The implications extend well beyond Lake Champlain. Thiamine Deficiency Complex is considered a major threat to conservation and restoration efforts for salmonines across a wide geographic range, and it has complicated recovery programs for Atlantic salmon, steelhead, and other species wherever thiamine-poor forage fish dominate adult diets. By revealing a previously unknown pathway for thiamine acquisition in the wild, the study opens the door to improved restoration strategies, more accurate field assessment of TDC, and better-informed management decisions for lake trout and related species across the Great Lakes and beyond.

For a species whose wild reproduction has frustrated managers for decades, the message is one of cautious optimism. The barriers to lake trout recovery remain real, from lamprey predation to habitat loss, but the new evidence suggests that one suspected obstacle, embryonic thiamine starvation in nature, may be less severe than hatchery data implied. Future work building on this experimental design could help managers distinguish which populations genuinely face thiamine-limited recruitment in the wild and which have been quietly rescuing themselves from the lake water all along.

Subject of Research: Thiamine uptake by lake trout embryos in natural versus laboratory incubation environments

Article Title: UVM study reveals how lake trout embryos acquire thiamine in the wild

Article References: UVM study reveals how lake trout embryos acquire thiamine in the wild. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: lake trout, thiamine, Thiamine Deficiency Complex, vitamin B1, Lake Champlain, Great Lakes, fish embryos, fisheries restoration, salmonines, aquatic ecology, Scientific Reports, conservation

The logic of the approach is elegantly simple. If a phage attacks only one host species, then adding that phage to a complex community is equivalent to performing a surgical deletion experiment: the targeted bacterium is depleted while the rest of the community, at least in principle, remains untouched. Any subsequent changes in the abundance or behavior of other members can then be attributed to the loss of the depleted organism, providing the kind of causal evidence that observational metagenomics alone cannot deliver. Despite this potential, phages have rarely been harnessed for this purpose, largely because isolating viruses with sufficiently narrow host ranges against ecologically relevant bacteria has been a technical bottleneck.

Hessler and colleagues overcame that bottleneck for the bacterial genus Variovorax, a group of soil and rhizosphere bacteria that has emerged as a key player in plant-associated communities. The team isolated nine phages that replicate in several ecologically important Variovorax species. Host-range testing showed that these viruses are strikingly specific: spot assays across multiple Variovorax strains revealed that only one of the nine phages, V45_66, was able to form plaques on more than a single host. That narrow specificity is precisely what makes the phages useful as experimental scalpels, since a broad-host-range virus would trigger cascading effects that would confound the interpretation of any community-level changes.

The researchers’ first test case came from a long-standing hypothesis about vitamin sharing. Variovorax had been predicted, on the basis of correlation network analyses, to engage in thiamine interdependencies with other community members—meaning that some organisms might rely on Variovorax to supply this essential B vitamin, or vice versa. To test this, the team worked with complex enrichment communities containing between 18 and 31 bacterial species, grown in the laboratory on different carbon sources including guar gum, locust bean gum, arabinogalactan, and konjac gum. These communities were allowed to stabilize over repeated passages, with pairwise Bray–Curtis dissimilarity analysis showing that their composition settled into a steady state by day eight to ten of the experiment.

Into these stabilized communities, the researchers introduced three of their Variovorax-specific phages, either individually or as a cocktail, targeting a strain designated Variovorax SCN45. Genome-resolved metagenomics—a technique that reconstructs the genomes of individual community members from mixed sequencing data and tracks their relative abundances over time—revealed a consistent reduction in Variovorax across all four enrichment cultures following phage application. Crucially, the depletion did not stop with Variovorax. One other population, a bacterium belonging to the genus Leifsonia, declined in relative abundance once its putative partner was gone, exactly as the correlation-based hypothesis of thiamine interdependence had predicted.

The decisive experiment came next. If Leifsonia was collapsing because it had lost access to Variovorax-produced thiamine, then simply adding thiamine to the culture should rescue it. That is precisely what the researchers observed: supplementation with 10 milligrams per liter of thiamine restored the Leifsonia population. Differential abundance screening, combined with statistical testing across the pre-phage, post-phage, and post-phage-plus-thiamine conditions, identified the Leifsonia population and two members of the family Microbacteriaceae as likely dependents on Variovorax-derived thiamine. Metagenome-assembled genome data for Leifsonia were consistent with the amplicon sequence variant analysis, and gene fitness profiling by RB-TnSeq showed that Variovorax SCN45 carries a complete thiamine biosynthesis operon alongside a type IV secretion system, both of which were highlighted in the community context. Together, these lines of evidence confirmed thiamine production as the mechanistic basis for the interdependence between Variovorax and Leifsonia, converting a statistical association into a verified biochemical relationship.

The team then extended the approach to a second, entirely different experimental system: a defined rhizosphere co-culture grown with Arabidopsis plants. In this system, a strain called Variovorax CL14 is known to degrade the plant hormone auxin produced by another bacterium, Arthrobacter CL28. Auxin is a central regulator of plant growth, and its degradation by Variovorax modulates how the plant responds to its microbial residents. Using phages v.cl_11 and v.cl_23, the researchers eliminated Variovorax CL14 from the co-culture. The result was a re-establishment of the stunted root phenotype, demonstrating that removing the auxin-degrading bacterium allowed the hormone to accumulate and suppress root growth. Growth curve experiments confirmed that the phages had no direct effect on Arthrobacter CL28 itself, reinforcing the specificity of the manipulation.

Beyond the specific findings about thiamine and auxin, the study carries a broader methodological significance. The enrichment communities in the experiments were monitored for stability, and haplotype frequency analysis was used to track evolutionary changes associated with phage exposure, giving the researchers a window into both ecological and evolutionary responses to viral attack. Supplementary analyses showed that the summed relative abundance of organisms encoding complete thiamine biosynthesis pathways shifted predictably across the experimental stages, and that the phage-induced perturbations were reproducible across independent carbon-source enrichments. This level of internal consistency strengthens the case that phage-mediated depletion can serve as a general-purpose tool for causal inference in microbiome science, complementing approaches such as gnotobiotic reconstruction, metabolic modeling, and isotope tracing.

The implications reach well beyond the laboratory. Microbiomes govern processes of enormous practical importance—from nutrient cycling in soils and plant health in agriculture to the functioning of bioreactors and, in medicine, the balance of human gut communities. A technique that allows researchers to remove a single species from a functioning community and observe the consequences could accelerate the identification of keystone organisms, the validation of cross-feeding networks, and ultimately the rational design of synthetic microbial consortia. The authors note that their experiments lay the foundation for research employing both wildtype and engineered phages to test interaction hypotheses and for targeted microbiome manipulation. Engineered phages, in particular, could in principle be designed to deliver payloads or to tune depletion dynamics with even finer control.

There are, of course, caveats and open questions. Phage infection itself can trigger physiological changes in the target host before lysis, and phage replication may impose selection pressure on the community, as suggested by the haplotype dynamics observed in this study. Host-range specificity, while an asset here, must be established case by case, and not every ecologically important bacterium has a culturable phage. Nevertheless, the demonstration that nine narrow-host-range phages could be isolated against Variovorax, and that three of them could cleanly test a metabolic interdependence hypothesis inside communities of up to 31 species, marks a substantial advance. The work, supported by the U.S. Department of Energy’s m-CAFEs Science Focus Area at Lawrence Berkeley National Laboratory, suggests a future in which viruses—long studied as pathogens of bacteria—become routine instruments for dissecting the hidden wiring of microbial ecosystems, one species at a time.

Subject of Research: Phage-based depletion of Variovorax to test microbial interactions in intact microbiomes

Article Title: Phage-based depletion of Variovorax reveals interactions within intact microbiomes

Article References: Hessler, T., Chiniquy, D., Adler, B. A., Hoff, J., Tucker, E., Huddy, R. J., Sachdeva, R., Lei, S., Harrison, S. T. L., Barrangou, R., Diamond, S., Deutschbauer, A. M., & Banfield, J. F. (2026). Phage-based depletion of Variovorax reveals interactions within intact microbiomes. Microbiome. https://doi.org/10.1186/s40168-026-02539-x

Image Credits: AI Generated

DOI: 10.1186/s40168-026-02539-x

Keywords: bacteriophages, microbiome, Variovorax, thiamine, cross-feeding, metagenomics, rhizosphere, Arabidopsis, auxin, Leifsonia, microbial interactions, phage therapy

Out-of-hospital cardiac arrest affects more than 3.7 million people worldwide each year, yet barely 10 percent of patients survive with favourable neurological function. For those who regain a pulse, the leading cause of death and long-term disability is hypoxic-ischaemic brain injury, produced by the initial global loss of blood flow during the arrest and amplified by reperfusion injury once circulation returns. This post-cardiac arrest syndrome involves a dysregulated cascade of systemic inflammation, oxidative stress, endothelial dysfunction, mitochondrial impairment, and neuroinflammation that continues to damage neurons even after resuscitation appears successful.

The STAR trial was designed around the idea that attacking several of these pathways simultaneously might succeed where single-agent approaches had failed. Hydrocortisone was chosen to dampen glucocorticoid-responsive inflammatory signalling and cytokine production; ascorbic acid to counter oxidative stress and support endothelial function; and thiamine to sustain pyruvate dehydrogenase-dependent mitochondrial energy metabolism. The combination had shown mixed results in sepsis, but no multicentre randomised trial had ever evaluated its early administration in comatose cardiac arrest survivors. The research team, led by Youn-Jung Kim and Won Young Kim, enrolled 160 adults aged 19 to 79 at four tertiary academic hospitals in South Korea between December 2021 and December 2024, with final follow-up completed in June 2025.

Participants, all comatose after resuscitation from presumed cardiac-cause arrest and all undergoing targeted temperature management, were randomly assigned in a one-to-one ratio to receive the drug combination or matching saline placebo. Treatment began quickly, at a median of 3.9 hours after cardiac arrest, and consisted of six intravenous infusions given every 12 hours over three days: hydrocortisone 100 mg, thiamine 200 mg, and ascorbic acid dosed at 50 mg/kg up to a maximum of 3 g per dose. The primary endpoint was the peak serum concentration of neuron-specific enolase, a well-validated biomarker of hypoxic-ischaemic brain injury, measured at 48 and 72 hours after return of spontaneous circulation. Secondary endpoints included survival at multiple timepoints, functional neurological outcomes on the Cerebral Performance Category and modified Rankin scales, organ failure trajectory, and length of intensive care and hospital stay.

The verdict on the primary endpoint was unambiguous. In the modified intention-to-treat population of 147 patients, peak neuron-specific enolase did not differ significantly between the treatment and placebo groups, with a median between-group difference of minus 5.9 ng/mL and a confidence interval spanning from minus 34.5 to plus 40.8, and a p value of 0.54. A sensitivity analysis in the full intention-to-treat population using multiple imputation for missing values produced the same conclusion. Serial biomarker modelling across the first 72 hours likewise showed no divergence in the trajectory of neuronal injury between the groups.

Clinical outcomes told the same story. At 180 days, 63.5 percent of treated patients in the primary analysis population were alive compared with 69.9 percent of placebo patients, a difference that was not statistically significant, and good neurological outcome was achieved by 54.1 percent versus 56.2 percent. There were no meaningful differences in time to awakening, organ failure scores, vasopressor requirements, or intensive care and hospital length of stay. Safety signals were balanced as well: roughly half of patients in each group experienced at least one serious adverse event, and none of these events were judged probably or definitely related to the study medications.

Intriguingly, the intervention was pharmacologically active. Serum vitamin C and thiamine concentrations rose sharply and significantly in the treated group by 72 hours, confirming that patients received and absorbed the drugs as intended. Yet this clear biochemical exposure failed to translate into biological protection of the brain. The authors suggest several explanations. All patients were already receiving targeted temperature management, which itself modulates cerebral metabolism and inflammatory responses, potentially leaving little incremental benefit for the drug cocktail. More fundamentally, the trial measured drug levels but not engagement of the intended molecular targets, so it cannot distinguish between failure to modulate the relevant pathways and failure of that modulation to prevent neuronal injury.

The trial also revealed something important about who was being treated: no participant had thiamine deficiency at baseline, and only about 31 percent had vitamin C deficiency. Universal supplementation of patients who are not deficient, the findings imply, is unlikely to help, and subgroup analyses provided no clear evidence that vitamin C status modified the treatment effect, though the trial was not powered to detect such interactions. This points the field toward phenotype-directed therapy, in which objectively confirmed micronutrient deficiency, rather than diagnosis alone, determines who receives supplementation.

The STAR results also align with a broader and increasingly cautionary literature. The VITAMINS trial found no benefit of the same triple combination in septic shock. The LOVIT trial reported that intravenous vitamin C increased the risk of death or persistent organ dysfunction in adults with sepsis, and the VITaCCA trial in cardiac arrest found worse organ-function, myocardial, renal, and neurological outcomes with a supraphysiological 10 g/day vitamin C regimen. Thiamine trials in both in-hospital and out-of-hospital cardiac arrest survivors showed no improvement in lactate clearance and were stopped early after mortality signals raised safety concerns. Together, these studies challenge the assumption that pharmacological doses of vitamins are inherently benign or beneficial in critically ill patients.

The trial’s investigators acknowledge limitations, including the exclusion of patients who died before 48 hours from the primary analysis, the awareness of treatment allocation by bedside clinicians, some open-label co-interventions in the placebo group, and restriction to four South Korean centres treating a predominantly cardiac-cause, temperature-managed population. Nevertheless, the central conclusion stands: early empiric administration of hydrocortisone, thiamine, and ascorbic acid cannot be recommended as a neuroprotective strategy for unselected comatose survivors of out-of-hospital cardiac arrest. Future research, the authors argue, should move beyond one-size-fits-all metabolic cocktails toward rigorously validated biological targets, confirmed deficiency states, and demonstrated target engagement before any new combination reaches the bedside.

Subject of Research: A randomised phase 2 trial of hydrocortisone, thiamine, and ascorbic acid for neuroprotection in comatose out-of-hospital cardiac arrest survivors

Article Title: Steroid, thiamine, and ascorbic acid for comatose out-of-hospital cardiac arrest survivors (STAR): a randomised, placebo-controlled, phase 2 trial

Article References: Kim, Y.-J., Ko, B. S., Roh, Y.-I., Kwon, H. J., Kim, S., Cha, K.-C., Kim, Y. H., & Kim, W. Y. (2026). Steroid, thiamine, and ascorbic acid for comatose out-of-hospital cardiac arrest survivors (STAR): a randomised, placebo-controlled, phase 2 trial. eClinicalMedicine, 100, Article 104191. https://doi.org/10.1016/j.eclinm.2026.104191

Image Credits: AI Generated

DOI: 10.1016/j.eclinm.2026.104191

Keywords: cardiac arrest, neuroprotection, hydrocortisone, thiamine, vitamin C, neuron-specific enolase, post-cardiac arrest syndrome, targeted temperature management, randomised controlled trial, ischaemia-reperfusion injury, critical care, metabolic resuscitation