Silicon Limitation Impairs the Tolerance of Marine Diatoms to Pristine Microplastics

Mechanisms of diatom inhibition by a new antifouling biocide with broad-spectrum efficacy against bacteria, algae, and barnacles

Marine biofouling, the accumulation of microorganisms, algae, and invertebrates on submerged surfaces, poses significant challenges for maritime industries. This study introduces a new biocide specifically designed to combat marine biofouling and assesses its efficacy and underlying algicidal mechanisms. The results showed that the biocide LaPT, synthesized by combining the rare-earth element Lanthanum (La) with pyrithione (PT), exhibited not only remarkable antibacterial properties but also strong algicidal activity against diatom species Amphora sp. and Thalassiosira pseudonana. Long-term field tests conducted in Xiamen Port, confirmed the effectiveness of LaPT-coated panels in reducing barnacle infestation. Algicidal mechanistic investigations through physiological, transgenic, and transcriptomic analyses revealed that LaPT disrupts cell wall and membrane integrity, interferes with calcium-dependent processes, and inhibits photosynthesis and energy metabolism, leading to diatom cell death. This study demonstrates the LaPT's effectiveness in preventing biofouling and reveal its unique mechanism of action, offering a promising solution for managing marine biofouling.

When microplastics meet microalgae: Unveiling the dynamic formation of aggregates and their impact on toxicity and environmental health

Microplastics (MPs) commonly coexist with microalgae in aquatic environments, can heteroaggregate during their interaction, and potentially affect the migration and impacts of MPs in aquatic environments. The hetero-aggregation may also influence the fate of other pollutants through MPs' adsorption or alter their aquatic toxicity. Here, we explored the hetero-aggregation process and its key driving mechanism that occurred between green microalga Chlorella vulgaris (with a cell size of 2-10 μm) and two types of MPs (polystyrene and polylactide, 613 μm). Furthermore, we investigated the environmental impacts of the microplastics-microalgae aggregates (MPs-microalgae aggregates) by comparing their adsorption of Cu(II) with that of pristine MPs and evaluating the effects of hetero-aggregation on MPs aging and their toxicity to microalgae. Our results indicated that microalgal colonization occurred on the surface of MPs, possibly through electrostatic interactions, hole-filling, hydrophilic interactions, and algae-bacteria symbiosis. The hetero-aggregation led to a stronger Cu(II) adsorption by MPs-microalgae aggregates than pristine MPs due to electrostatic interactions, coordination, complexation, and ion exchange. Exposure to either MPs (pristine or aged) or Cu(II) inhibited the cell growth of C. vulgaris, while the integrated biomarker response (IBR) showed more pronounced inhibitory effects resulting from aged MPs compared to pristine MPs and an antagonistic effect on microalgae was caused by the co-exposure to MPs and Cu(II). These findings suggest that the hetero-aggregation of MPs and microalgae may alter their environmental fates and co-pollutant toxicity.

Phytoremediation of microplastics by water hyacinth

Microplastics have emerged as pervasive environmental pollutants, posing significant risks to both terrestrial and aquatic ecosystems worldwide. Current remediation strategies-including physical, chemical, and microbial methods-are inadequate for large-scale, in situ removal of microplastics, highlighting the urgent need for alternative solutions. Phytoremediation, an eco-friendly and cost-effective technology, holds promise in addressing these challenges, though its application to microplastic pollution remains underexplored. Here we show the capacity of Eichhornia crassipes (water hyacinth), a fast-growing, floating aquatic plant, to remove microplastics from contaminated water. Our results show that within 48 h, water hyacinth achieved removal efficiencies of 55.3 %, 69.1 %, and 68.8 % for 0.5, 1, and 2 μm polystyrene particles, respectively, with root adsorption identified as the primary mechanism. Fluorescence microscopy revealed that the extremely large and abundant root caps, featuring a total surface area exceeding 150,000 mm2 per plant, serve as the principal sites for the entrapment of microplastics. Furthermore, a unique "vascular ring" structure within the stem prevents the translocation of microplastics to aerial tissues, safeguarding leaves for potential downstream applications. This study offers the first microstructural insight into the mechanisms underpinning water hyacinth's exceptional microplastic adsorption capacity and resilience, providing a promising framework for developing phytoremediation strategies to mitigate microplastic pollution in aquatic ecosystems.

Microplastic pollution in aquatic ecosystems: impacts on diatom communities

In recent years, heightened concern has emerged regarding the pervasive presence of microplastics in the environment, particularly in aquatic ecosystems. This concern has prompted extensive scientific inquiry into microplastics' ecological and physiological implications, including threats to biodiversity. The robust adsorption capacity of microplastic surfaces facilitates their widespread distribution throughout aquatic ecosystems, acting also as carriers of organic pollutants. However, to comprehensively understand the broader implications of this pollution, a thorough examination of the origins, composition, and widespread distribution of microplastics within aquatic biotopes is imperative. Diatoms, unicellular photosynthetic organisms, play a pivotal role in aquatic ecosystems as primary producers, forming the base of the aquatic food web. Investigating the relationship between microplastics and diatoms, leveraging methodological advancements, holds promise in unraveling the intricate action mechanisms underlying their interactions. Such inquiry sheds light on the physiological responses elicited and provides crucial insights into the ecological dynamics within aquatic environments. This study explores the understanding of microplastic-diatom interactions, focusing on how microplastic types, sizes, and concentrations influence diatoms. Ultimately, the current study strongly advocates for transdisciplinary collaborations, such as partnerships between ecologists, materials scientists, and policymakers, as the complexity of microplastic pollution demands collective efforts to address this critical and alarming environmental issue.

Unraveling the toxicity mechanisms of nanoplastics with various surface modifications on Skeletonema costatum: Cellular and molecular perspectives

Nanoplastics are ubiquitous in marine environments, exhibiting high bioavailability and potential toxicity to marine organisms. However, the impacts of nanoplastics with various surface modifications on marine microalgae remain largely unexplored. This study explored the toxicity mechanisms of two nanoplastic types-polystyrene (PS) and polymethyl methacrylate (PMMA)-with distinct surface modifications on Skeletonema costatum at cellular and molecular levels. Results showed that nanoplastics significantly impaired the growth of microalgae, particularly PS-NH2, which caused the most pronounced growth inhibition, reaching 56.99 % after a 96-h exposure at 50 mg/L. Transcriptomic profiling revealed that nanoplastics disrupted the expression of genes predominantly involved in ribosome biogenesis, aminoacyl-tRNA biosynthesis, amino acid metabolism, and carbohydrate metabolism pathways. The integrated biochemical and transcriptomic evidence highlighted that PS-NH2 nanoplastics had the most adverse impact on microalgae, affecting fundamental pathways such as ribosome biogenesis, energy metabolism, photosynthesis, and oxidative stress. Our findings underscore the influence of surface-modified nanoplastics on algal growth and contribute new understanding to the toxicity mechanisms of these nanoplastics in marine microalgae, offering critical information for assessing the risks of emerging pollutants.

The interaction mechanisms of algal organic matter (AOM) and various types and aging degrees of microplastics

Algal blooms can produce substantial amounts of algal organic matter (AOM). Microplastics (MPs) in aquatic environments inevitably interact with AOM. Meanwhile, the aging and type of MPs may increase the uncertainty surrounding interaction. This study focused on polyethylene (PE) and polylactic acid (PLA) to investigate their interaction with AOM before and after aging. The results shw that PLA has a stronger adsorption capacity for AOM than PE. Meanwhile, aging enhanced and weakened the adsorption of PE and PLA for AOM. Compared to unaged PE (UPE) and aged PLA (APLA), aged PE (APE) and unaged PLA (UPLA) more significantly promote the humification of AOM and alter its functional groups. 2D-IR-COS analysis reveals that the sequence of functional group changes in AOM interacting with MPs is influenced by the type and aging of MPs. After interacting with AOM, surface roughness increased for all MPs. FTIR and XPS analyses show that the addition of AOM accelerated the oxidation of MPs surfaces, especially for UPE and APLA, with oxygen content increasing by 9.32 % and 1 %. Aging enhances the interaction between PE and AOM, while weakening the interaction between PLA and AOM. These findings provide new insights into understanding the interplay between AOM and MPs.

Nanoplastics impair growth and nitrogen fixation of marine nitrogen-fixing cyanobacteria

Nanoplastics pollution is a growing environmental problem worldwide. Recent research has demonstrated the toxic effects of nanoplastics on various marine organisms. However, the influences of nanoplastics on marine nitrogen-fixing cyanobacteria, a critical nitrogen source in the ocean, remained unknown. Here, we report that nanoplastics exposure significantly reduced growth, photosynthetic, and nitrogen fixation rates of Crocosphaera watsonii (a major marine nitrogen-fixing cyanobacterium). Transcriptomic analysis revealed that nanoplastics might harm C. watsonii via downregulation of photosynthetic pathways and DNA damage repair genes, while genes for respiration, cell damage, nitrogen limitation, and iron (and phosphorus) scavenging were upregulated. The number and size of starch grains and electron-dense vacuoles increased significantly after nanoplastics exposure, suggesting that C. watsonii allocated more resources to storage instead of growth under stress. We propose that nanoplastics can damage the cell (e.g., DNA, cell membrane, and membrane-bound transporters), inhibit nitrogen and carbon fixation, and hence lead to nutrient limitation and impaired growth. Our findings suggest the possibility that nanoplastics pollution could reduce the new nitrogen input and hence affect the productivity in the ocean. The impact of nanoplastics on marine nitrogen fixation and productivity should be considered when predicting the ecosystem response and biogeochemical cycling in the changing ocean.

Optimization of microplastic removal based on the complementarity of constructed wetland and microalgal-based system

As one of the emblematic emerging contaminants, microplastics (MPs) have aroused great public concern. Nevertheless, the global community still insufficiently acknowledges the ecological health risks and resolution strategies of MP pollution. As the nature-based biotechnologies, the constructed wetland (CW) and microalgal-based system (MBS) have been applied in exploring the removal of MPs recently. This review separately presents the removal research (mechanism, interactions, implications, and technical defects) of MPs by a single method of CWs or MBS. But one thing with certitude is that the exclusive usage of these techniques to combat MPs has non-negligible and formidable challenges. The negative impacts of MP accumulation on CWs involve toxicity to macrophytes, substrates blocking, and nitrogen-removing performance inhibition. While MPs restrict MBS practical application by making troubles for separation difficulties of microalgal-based aggregations from effluent. Hence the combined strategy of microalgal-assisted CWs is proposed based on the complementarity of biotechnologies, in an attempt to expand the removing size range of MPs, create more biodegradable conditions and improve the effluent quality. Our work evaluates and forecasts the potential of integrating combination for strengthening micro-polluted wastewater treatment, completing the synergistic removal of MP-based co-pollutants and achieving long-term stability and sustainability, which is expected to provide new insights into MP pollution regulation and control.

Impact of facemask debris on marine diatoms: Physiology, surface properties, sinking rate, and copepod ingestion

Discarded surgical masks have become a new source of plastic waste in seawater capable of releasing numerous micro and nano plastic fragments. However, little information is available about how this waste impacts the ecological state of marine phytoplankton. Here, we exposed two model marine diatoms (Phaeodactylum tricornutum and Thalassiosira weissflogii) to mask-released debris (MD) that is characterized by various differently-charged functional groups. Although MD could only bind loosely to diatoms, it still inhibited their growth and significantly altered cell surface physicochemical properties. At the nanoscale, MD-exposed cell walls showed enhanced roughness and modulus, besides declined electrical potential, adhesion, and proportion of oxygen-containing compounds. As a result, diatom ingestion by copepods was reduced, and the sinking rate of the carbon pool consisting of MD plus diatoms decreased as well. Our study indicated that MD effects on diatoms have the potential to slow down carbon export from surface seawater to the deep sea. Since oxidation and generation of functional groups are common during the aging process of microplastics (MPs) in nature, the interactions between the diatom cell surface and MD have important environmental significance.

Tracking Nano- and Microplastics Accumulation and Egestion in a Marine Copepod by Novel Fluorescent AIEgens: Kinetic Modeling of the Rhythm Behavior

Nano- and microplastics (NMPs) are now prevalent in the marine environment. This study quantified the uptake and depuration kinetics of spherical polystyrene NMPs of different particle sizes (200 nm/30 μm) and functional groups (-NH2/-COOH) in a temperate calanoid copepod Calanus sinicus (C. sinicus), which exhibited rhythmic feeding patterns in natural environments. Aggregated-induced emission (AIE) fluorescent probes were employed to track and quantify the kinetics of NMPs with excellent photostability and biocompatibility. The results showed that C. sinicus consumed all NMPs types, with preference of NMPs to small size and amino group. Increased diatom concentrations also inhibited the bioaccumulation of NMPs. Influenced by rhythmic behavior, the bioaccumulation of NMPs by C. sinicus was nonstationary during the 6 h uptake phase. After 1-3 h of rapid uptake, the body burden peaked and then slowly declined. During the 3 h depuration phase, C. sinicus rapidly and efficiently removed NMPs with a mean half-life of only 0.23 h. To further quantify the body burden of C. sinicus under the influence of rhythmic feeding behavior, a biokinetic model was established, and the Markov chain Monte Carlo method was used to estimate the parameter distribution. Our results highlighted that copepods exhibited unique rhythmic feeding behavior under environmentally relevant concentrations of NMPs exposure, which may influence the bioaccumulation, trophic transfer, and environmental fate of NMPs.

Microbial community dynamics and assembly mechanisms across different stages of cyanobacterial bloom in a large freshwater lake

Cyanobacterial bloom caused by eutrophication in lakes has become one of the significant environmental problems worldwide. However, a notable research gap persists in understanding the environmental adaptation and community assembly of microbial dynamics in response to different blooming stages. Therefore, metagenomic sequencing was employed in this study to investigate alterations in the microbial community composition in water and sediment during different stages of cyanobacterial blooms in Lake Taihu. The results indicated significant spatiotemporal variations in physicochemical parameters across the early, medium, and late stages of a complete cyanobacteria bloom cycle. Diversity analysis further revealed that the temporal differences in the microbial community were substantially greater than spatial variations. Notably, during the medium-blooming stages in water, Microcystis emerged as the predominant detected cyanobacteria genus. Interestingly, the content of superoxide dismutase (SOD), malondialdehyde (MDA), and catalase (CAT) in sediment exceeded those in water by over 10 times, indicating that sediment-dwelling Cyanobacteria might constitute a crucial source of water blooms. Moreover, dissolved oxygen, pH, and water temperature were identified as the most influential environmental variables shaping the microbial community in the water. Stochasticity emerged as a prominent factor governing microbial community assembly across different bloom periods. Meanwhile, co-occurrence patterns suggested fewer interactions and instability between species in medium-blooming stages. Notably, the potential keystone phyla occupied crucial ecological niches. This research carries significant theoretical implications for managing cyanobacterial blooms in freshwater ecosystems.

Microplastics Reshape the Fate of Aqueous Carbon by Inducing Dynamic Changes in Biodiversity and Chemodiversity

The interactions among dissolved organic matter (DOM), microplastics (MPs) and microbes influence the fate of aqueous carbon and greenhouse gas emissions. However, the related processes and mechanisms remain unclear. Here, we found that MPs determined the fate of aqueous carbon by influencing biodiversity and chemodiversity. MPs release chemical additives such as diethylhexyl phthalate (DEHP) and bisphenol A (BPA) into the aqueous phase. The microbial community, especially autotrophic bacteria such as Cyanobacteria, showed a negative correlation with the additives released from MPs. The inhibition of autotrophs promoted CO₂ emissions. Meanwhile, MPs stimulated microbial metabolic pathways such as the tricarboxylic acid (TCA) cycle to accelerate the DOM biodegradation process, and then the transformed DOM presented low bioavailability, high stability, and aromaticity. Our findings highlight an urgent need for chemodiversity and biodiversity surveys to assess ecological risks from MP pollution and the impact of MPs on the carbon cycle.

From promoting aggregation to enhancing obstruction: A negative feedback regulatory mechanism of alleviation of trivalent chromium toxicity by silicon in rice

Trivalent chromium [Cr(III)] is a threat to the environment and crop production. Silicon (Si) has been shown to be effective in mitigating Cr(III) toxicity in rice. However, the mechanisms by which Si reduces Cr(III) uptake in rice are unclear. Herein, we hypothesized that the ability of Si to obstruct Cr(III) diffusion via apoplastic bypass is related to silicic acid polymerization, which may be affected by Cr(III) in rice roots. To test this hypothesis, we employed hydroponics experiments on rice (Oryza sativa L.) and utilized apoplastic bypass tracer techniques, as well as model simulations, to investigate 1) the effect of Si on Cr(III) toxicity and its obstruction capacity via apoplastic bypass, 2) the effect of Cr(III) on silicic acid polymerization, and 3) the relationship between the degree of silicic acid polymerization and its Cr(III) obstruction capacity. We found that Si reversed the damage caused by Cr(III) stress in rice. Si exerted an obstruction effect in the apoplast, significantly decreasing the share of Cr(III) uptake via the apoplastic bypass from 18% to 11%. Moreover, Cr(III) reduced silica particles' radii and increased Si concentration in roots. Modeling revealed that a 5-fold reduction in their radii decreased the diffusion of Cr(III) in apoplast by approximately 17%. We revealed that Cr(III) promoted silicic acid polymerization, resulting in the formation of a higher number of Si particles with a smaller radius in roots, which in turn increased the ability of Si to obstruct Cr(III) diffusion. This negative feedback regulatory mechanism is novel and crucially important for maintaining homeostasis in rice, unveiling the unique role of Si under Cr(III) ion stress and providing a theoretical basis for promoting the use of Si fertilizer in the field.