The study examined how manganese content affected the corrosion behavior of three Cu–Mn cladding layers fabricated on Q235 steel. The layers contained 10 wt%, 15 wt%, or 20 wt% Mn and were immersed for 180 days in seawater containing Chlorella or diatoms. All three compositions showed low microalgal coverage, but the 20 wt% Mn layer produced the smallest values in both test solutions. The researchers attributed the improved inhibition to the structure of the corrosion-product layer rather than to a difference in the duration of testing: increasing manganese content promoted internal-stress accumulation, which accelerated cracking and flaking of corrosion products.

This mechanism matters because copper alloys are widely used in ships and marine engineering equipment for their antifouling performance. Over long service periods, however, the corrosion-product layer can become denser while microalgae attach to the surface, progressively degrading the material’s ability to resist fouling. In the tested Cu–Mn coatings, the corrosion products instead formed a loose, heavily cracked layer that could readily flake away. As manganese content increased, that layer became more susceptible to cracking and detachment, supporting continued copper-ion release into the surrounding water.

The released copper ions were linked to elevated intracellular reactive oxygen species, or ROS, in attached microalgae. The study’s proposed mechanism is that manganese-induced changes in the corrosion layer enhance copper-ion release, increasing oxidative stress within the organisms. The authors reported that the higher ROS level was associated with extensive apoptosis and effective suppression of attachment. The results therefore connect an observable coating behavior—cracking and flaking of corrosion products—with the biological endpoint of reduced microalgal colonization, although the supplied abstract does not provide the numerical copper-release or ROS measurements needed to quantify those intermediate steps.

The experiment provides a laboratory comparison of manganese content under a defined 180-day immersion period, rather than a direct field trial of coated marine structures. Its findings nevertheless offer a technically focused route for improving durable antifouling metal surfaces: adding more manganese to the Cu–Mn cladding changed the evolving corrosion layer in a way associated with stronger inhibition of two types of microalgae. The 20 wt% Mn composition achieved the best reported outcome, with coverage remaining at only 5.81% for Chlorella and 2.52% for diatoms, but the evidence does not establish how the coatings would perform across other organisms, exposure conditions or real-world service environments.

Subject of Research: Effects of manganese content on corrosion and microalgal attachment in Cu–Mn laser-cladded Q235 steel.

Article Title: Cu–Mn laser cladding layers on Q235 steel: the influence of Mn content on corrosion behavior and long-term microalgal inhibitory performance

Article References: Li, J., Liu, Z., Liu, J., Zeng, G., Wang, X., Yang, H., Ning, H., & Li, M. (2026). Cu–Mn laser cladding layers on Q235 steel: the influence of Mn content on corrosion behavior and long-term microalgal inhibitory performance. Journal of Materials Science, 61(41), 32076-32106. https://doi.org/10.1007/s10853-026-13665-0

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13665-0

Keywords: Cu–Mn coatings, laser cladding, manganese, Q235 steel, marine antifouling, corrosion products, microalgae, Chlorella, diatoms, reactive oxygen species, laser, cladding

The research team, led by Nur Aini Azizah of Brawijaya University and involving scientists from Indonesia’s National Research and Innovation Agency (BRIN), set out to test a question that has received surprisingly little attention: what happens to marine algae when they are exposed to the dissolved chemicals that seep out of degrading biodegradable plastics? While conventional plastics such as polyethylene and polystyrene have been studied extensively for their effects on aquatic life, biodegradable variants have often been assumed to be benign. The new study challenges that assumption with hard numbers.

The experiment focused on three species of marine microalgae that play important roles in coastal ecosystems and aquaculture: Chlorella sp., Tetraselmis sp., and Navicula sp. These organisms were chosen because they are widely used in toxicity testing, reproduce quickly, and respond measurably to chemical stress. Before any biological testing began, the researchers used Fourier Transform Infrared spectroscopy, or FTIR, to confirm the polymer identity of the biodegradable polypropylene material used in their experiments. This analytical step matters because the market for biodegradable plastics is crowded with materials of uncertain composition, and verifying what was actually tested is essential for reproducibility.

Toxicity assays were conducted under controlled laboratory conditions following a standard 96-hour exposure window, a protocol consistent with internationally recognized guidelines for static toxicity testing with microalgae. The researchers measured growth by tracking changes in cell density over time, and for species showing significant inhibition, they also measured chlorophyll-a content, the pigment at the heart of photosynthesis. A drop in chlorophyll-a signals more than slower division; it indicates that the cellular machinery of energy capture itself is being disrupted, which can cascade through growth, reproduction, and ultimately the productivity of entire algal communities.

The first round of testing, a preliminary range-finder phase, revealed something ecologically important: the three algal species did not respond uniformly. Navicula sp., a diatom, showed no clear concentration-dependent inhibition of growth, and the team therefore excluded it from the definitive test. That kind of species-specific variation is a recurring theme in microplastic toxicology. It suggests that the ecological consequences of plastic leachates will not be evenly distributed across marine communities, and that some groups of organisms may be quietly bearing the brunt of chemical exposure while others appear unaffected.

The definitive testing on the two remaining species produced striking results. Chlorella sp. proved to be the most sensitive organism, with a 96-hour median inhibition concentration, or IC50, of just 0.49 milligrams per liter. In practical terms, that means the leachate from biodegradable polypropylene microplastics cut Chlorella growth in half at a concentration of less than half a milligram of leachate per liter of water. Tetraselmis sp. was also affected in a concentration-dependent manner, but it required a far higher dose, with an IC50 of 37.84 milligrams per liter, roughly 77 times greater than the threshold for Chlorella.

That nearly two-order-of-magnitude difference in sensitivity between two green microalgae is one of the most technically interesting aspects of the study. It underscores why single-species toxicity tests, while useful, can be misleading when extrapolated to ecosystems. If regulators were to rely on Tetraselmis alone as a test organism, they might conclude that biodegradable polypropylene leachates pose only a modest hazard. The extreme vulnerability of Chlorella tells a different story. Species sensitivity distributions, which pool responses across many organisms, are increasingly seen as the more defensible basis for environmental risk assessment, and this study provides data points for exactly that kind of framework.

The environmental context of the work is grounded in the Indonesian archipelago, a region where plastic pollution is severe and well documented. Complementary field observations on microplastic occurrence along Indonesian coasts, cited by the authors, underscore the relevance of the laboratory findings. Previous studies have catalogued microplastics in the coastal waters of Surabaya, in mangrove sediments near Jakarta, and in fish from local markets, establishing that plastic fragments are pervasive in Indonesian marine environments. As biodegradable plastics enter those same waters, their fragmentation into microplastics and the subsequent release of leachates becomes a realistic exposure scenario rather than a theoretical one.

The new results also fit into a broader international picture. Earlier research has shown that plastic leachates can impair growth and oxygen production in Prochlorococcus, the ocean’s most abundant photosynthetic bacterium, and that leachates from weathered plastics can be more toxic than those from pristine materials. Other studies have documented leachate effects on coral fertilization, mussel larvae, and benthic invertebrates. What the Indonesian team adds is a specific demonstration that biodegradable polypropylene, a material promoted partly on the assumption that it solves the persistence problem, can generate dissolved chemicals capable of measurable sublethal harm to marine primary producers at low concentrations.

The authors are careful to frame their work as an initial toxicity assessment, and that caution is warranted. The study does not identify the specific chemical compounds responsible for the inhibition, does not examine effects beyond 96 hours, and does not test whether environmentally realistic leachate concentrations overlap with the doses that harmed Chlorella in the laboratory. Long-term, multigenerational studies, chemical characterization of the leachates, and field validation will all be needed before the ecological risk can be quantified. Nevertheless, the central message is difficult to ignore: biodegradability is not the same as harmlessness. As the world races to replace conventional plastics with alternatives, the new findings argue that every substitute material deserves the same rigorous ecotoxicological scrutiny that the originals received, before it is deployed at planetary scale.

Subject of Research: Toxicity of biodegradable polypropylene microplastic leachates to marine microalgae

Article Title: Growth and chlorophyll-a responses of marine microalgae to biodegradable polypropylene microplastic leachates: an initial toxicity assessment

Article References: Azizah, N. A., Sartimbul, A., Herawati, E. Y., Permadi, S., Gautama, B. G., Darmayati, Y., Risandi, J., & Hindarti, D. (2026). Growth and chlorophyll-a responses of marine microalgae to biodegradable polypropylene microplastic leachates: an initial toxicity assessment. Ecotoxicology, 35(8), Article 181. https://doi.org/10.1007/s10646-026-03157-x

Image Credits: AI Generated

DOI: 10.1007/s10646-026-03157-x

Keywords: biodegradable plastics, polypropylene, microplastics, leachates, marine microalgae, Chlorella, Tetraselmis, Navicula, chlorophyll-a, IC50, ecotoxicology, Indonesia

The research team isolated four bacterial strains from lake sediment and identified them through 16S rRNA gene sequencing, the standard molecular method for pinning down bacterial identity. The four isolates belonged to the genera Serratia, Proteus and Pseudomonas, and were designated Serratia N-1, Proteus N-2, Pseudomonas F5-2 and Pseudomonas F11. Each strain was then tested against two species of green microalgae, Chlorella and Micractinium, under three distinct nutritional regimes: purely autotrophic conditions in which the algae relied entirely on photosynthesis, mixotrophic conditions supplemented with glucose, and systems supplemented with sucrose instead. This experimental design allowed the researchers to isolate the effect of carbon availability and carbon chemistry on the outcome of each bacteria-algae encounter.

Under autotrophic conditions, the picture was one of striking asymmetry. None of the four bacterial strains showed meaningful inhibition of Chlorella, yet all of them suppressed Micractinium by roughly 20 percent. Intriguingly, there was no significant difference between treatments using live bacterial cultures and treatments using only cell-free supernatants, the liquid fraction left after the bacteria were removed. That equivalence carried an important mechanistic clue: whatever was harming Micractinium was not the bacteria themselves through direct contact, but soluble, extracellular metabolites that the bacteria had released into the medium. The algae were being felled by chemistry, not by physical attack.

The addition of glucose transformed the entire dynamic. In mixotrophic cultures containing this simple sugar, algicidal performance against Chlorella, previously negligible, surged. Serratia N-1 became a devastating antagonist, achieving more than 99 percent inhibition of Chlorella growth within just three days. The other strains followed the same direction but at different magnitudes and speeds: Proteus N-2 reached 79 percent inhibition by day seven, Pseudomonas F11 reached 60 percent, and Pseudomonas F5-2 reached 47 percent. Once again, supernatants performed comparably to whole cultures, reinforcing the conclusion that extracellular metabolites, whose production or potency is boosted when the bacteria can feed on glucose, are the dominant weapons in this interaction.

Micractinium, however, told a different story under the same glucose conditions. Only the live culture of Serratia N-1 exhibited strong inhibition against this alga. Its cell-free supernatant had no effect, and neither did any of the other three strains, whether as cultures or supernatants. This pattern suggests that Serratia N-1 attacks Micractinium through a mechanism that requires the living bacterium, possibly contact-dependent activity or a metabolite that is unstable, rapidly degraded, or produced only in the immediate vicinity of intact cells. The contrast with the supernatant-driven attack on the same alga under autotrophic conditions implies that the bacterium can deploy fundamentally different modes of action depending on its nutritional environment and its target.

The most dramatic reversal came when glucose was swapped for sucrose. In the disaccharide systems, the algicidal capacity of all four strains was largely weakened, and in one case the relationship inverted entirely. Serratia N-1, which had annihilated Chlorella cultures in the presence of glucose, switched roles and became a growth promoter, increasing Chlorella biomass fivefold. A microorganism that functioned as a near-total algicide under one carbon regime became, under another, an effective biofertilizer for the very same algal species. The authors attribute these shifts to the presence and type of organic carbon sources in the co-culture systems, which significantly modulate bacterial algicidal phenotypes.

The technical implications of this carbon-dependent switching are considerable. Algicidal bacteria are widely explored as biological control agents against harmful algal blooms, which are increasing in frequency and intensity worldwide as eutrophication and warming waters create ideal conditions for explosive algal growth. Cyanobacterial blooms in particular produce toxins such as microcystins that threaten drinking water supplies, fisheries, recreation and public health. Conventional chemical algicides can leave toxic residues and damage non-target organisms, which is why microbial control, with its promise of environmental sustainability and high efficiency, has attracted growing interest. But the new findings show that a candidate biocontrol strain cannot be evaluated in isolation from the chemistry of the water body it is meant to treat.

Organic carbon is not a uniform background variable in natural waters. Dissolved organic carbon arrives from decaying vegetation, agricultural runoff, wastewater discharge and the algae themselves, and its composition varies enormously across systems and seasons. A lake receiving glucose-rich runoff may behave very differently from one dominated by more complex sugars or by carbon-poor conditions. The study suggests that in carbon-rich environments containing readily metabolizable sugars, bacterial antagonists of algae may become dramatically more lethal, while in systems where the dominant carbon sources resemble sucrose, the same bacteria might lose their killing power or even stimulate the algae they were intended to suppress. Any field deployment of algicidal bacteria would therefore need to account for the carbon fingerprint of the target water body.

The results also illuminate the broader ecology of algae-bacteria interactions, a relationship that ranges from mutualism to parasitism and is increasingly recognized as a central regulator of aquatic ecosystems. Previous research has shown that bacteria can promote algal growth by supplying vitamins, hormones such as indole-3-acetic acid, or quorum-sensing molecules, and the same research group has previously exploited growth-promoting bacteria to boost biomass accumulation of Chlorella for bioenergy applications. The new work demonstrates that a single bacterial strain can occupy multiple points on this mutualism-antagonism spectrum simultaneously, with nutrition acting as the switch. Understanding the metabolic logic behind these switches, which sugars trigger toxin production, which suppress it, and why the two algal species respond so differently, could allow researchers to design interactions rather than merely observe them.

For now, the study delivers a clear and sobering message wrapped in an exciting discovery: the battle lines between bacteria and algae are drawn in sugar. Serratia N-1’s ability to wipe out more than 99 percent of a Chlorella culture in three days marks it as one of the most potent algicidal agents reported against this genus, while its fivefold growth-promoting effect under sucrose shows the same strain could serve biofuel and biomass production instead. The authors present the work as a scientific basis for understanding algae-bacteria interactions and the nutritional regulation of algicidal activity under varying carbon environments. As harmful blooms intensify across the globe, the ability to predict, and perhaps one day deliberately tune, these microbial relationships by managing organic carbon could become a decisive tool in the effort to keep the world’s waters clear.

Subject of Research: Carbon-source-dependent algicidal activity of lake-sediment bacteria against Chlorella and Micractinium

Article Title: Differential responses of Chlorella and Micractinium to algicidal bacteria in varying organic carbon environments

Article References: Zhang, B., Zhang, F., Wang, X., Ji, Z., Li, H., Zhang, Z., & Su, Y. (2026). Differential responses of Chlorella and Micractinium to algicidal bacteria in varying organic carbon environments. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38264-z

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38264-z

Keywords: algicidal bacteria, Chlorella, Micractinium, Serratia, Pseudomonas, harmful algal blooms, organic carbon, glucose, sucrose, mixotrophic culture, microbial control, algae-bacteria interactions