Bacterial and fungal assemblages and functions associated with biofilms differ between diverse types of plastic debris in a freshwater system

Performance evaluation of the effect of humic acid on Anammox granular sludge: Apparent morphology, nitrogen removal and microbial community

Humic acid (HA) is a typical refractory organic matter, so it is of great significance to investigate its effect on the performance of Anammox granular sludge. When the dosage of HA ≤ 50 mg/L, HA promotes the total nitrogen removal rate (NRR) to 1.45 kg/(m3·day). When HA was between 50 and 100 mg/L, the NRR of Anammox was stable. At this time, the adsorption of HA causes the sludge to gradually turn from red to brown, but the activities of heme and enzymes showed that its capacity was not affected. When HA levels reached 250 mg/L, the NRR dropped to 0.11 kg/(m3·day). Moderate HA levels promoted the release of extracellular polymeric substance (EPS), but excessive HA levels lead to a decrease in EPS concentrations. HA inhibited Anammox activity, which indirectly hindered the transmission of substrate and accumulated substrate toxicity. Although HA promoted the increase of heterotrophic microbial abundance in Anammox system, the microbial diversity decreased gradually. With the increase of HA concentration, the abundance of Candidatus_Brocadia, the main functional microorganism of Anammox system, decreased gradually, while the abundance of Candidatus_Kuenenia increased gradually.

Structural properties and microbial diversity of the biofilm colonizing plastic substrates in Terra Nova Bay (Antarctica)

Microbial colonization on plastic polymers has been extensively explored, however the temporal dynamics of biofilm community in Antarctic environments are almost unknown. As a contribute to fill this knowledge gap, the structural characteristics and microbial diversity of the biofilm associated with polyvinyl chloride (PVC) and polyethylene (PE) panels submerged at 5 m of depth and collected after 3, 9 and 12 months were investigated in four coastal sites of the Ross Sea. Additional panels placed at 5 and 20 m were retrieved after 12 months. Chemical characterization was performed by FTIR-ATR and Raman (through Surface-Enhanced Raman Scattering, SERS) spectroscopy. Bacterial community composition was quantified at a single cell level by Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH) and Confocal Laser Scanning Microscopy (CLSM); microbial diversity was assessed by 16S rRNA gene sequencing. This multidisciplinary approach has provided new insights into microbial community dynamics during biofouling process, shedding light on the biofilm diversity and temporal succession on plastic substrates in the Ross Sea. Significant differences between free-living and microbial biofilm communities were found, with a more consolidated and structured community composition on PVC compared to PE. Spectral features ascribable to tyrosine, polysaccharides, nucleic acids and lipids characterized the PVC-associated biofilms. Pseudomonadota (among Gamma-proteobacteria) and Alpha-proteobacteria dominated the microbial biofilm community. Interestingly, in Road Bay, close to the Italian "Mario Zucchelli" research station, the biofilm growth - already observed during summer season, after 3 months of submersion - continued afterwards leading to a massive microbial abundance at the end of winter (after 12 months). After 3 months, higher percentages of Gamma-proteobacteria in Road Bay than in the not-impacted site were found. These observations lead us to hypothesize that in this site microbial fouling developed during the first 3 months could serve as a starter pioneering community stimulating the successive growth during winter.

New insights of bacterial and eukaryotic phenotypes on the plastics collected from the typical natural habitat of the endangered crocodile lizard

Although accumulating evidence indicates that endangered animals suffer from plastic pollution, this has been largely overlooked. Here, we explored the bacteria and eukaryotes living in the plastics gathered from the natural habitat of the highly endangered crocodile lizard. The results demonstrated that the bacterial and eukaryotic communities on plastics formed a unique ecosystem that exhibited lower diversity than those in the surrounding water and soil. However, microbes displayed a more complex and stable network on plastic than that in water or soil, implying unique mechanisms of stabilization. These mechanisms enhanced their resilience and contributed to the provision of stable ecological services. Eukaryotes formed a simpler and smaller network than bacteria, indicating different survival strategies. The bacteria residing on the plastics played a significant role in carbon transformation and sequestration, which likely impacted carbon cycling in the habitat. Furthermore, microbial exchange between plastics and the crocodile lizard was observed, suggesting that plastisphere serves as a mobile gene bank for the exchange of information, including potentially harmful substances. Overall, microbes on plastic appear to significantly impact the crocodile lizard and its natural habitat via various pathways. These results provided novel insights into risks evaluation of plastic pollution and valuable guidance for government efforts in plastic pollutant control in nature reserves.

Microplastics alter the microbiota-mediated phosphorus profiles at sediment-water interface: Distinct microbial effects between sediment and plastisphere

Microplastics (MPs) are ubiquitous in freshwater sediments, raising concern about their potential impacts on ecosystem services. However, the specific impacts of microbiota mediated by MPs in sediment and plastisphere compartments on P availability remain elusive. This investigation conducted a series of microcosm experiments utilizing eutrophic lake sediment amended with fuel-based polyethylene terephthalate (PET), bio-based polylactic acid (PLA) MPs, and a natural cobblestone substrate to unravel their effects. The findings highlighted that MPs induced alterations in bacterial communities in both sediment and plastisphere, consequently modifying P availabilities at the sediment-water interface (SWI). In comparison to non-biodegradable PET, biodegradable PLA MPs presented higher proportions of specific bacteria and functional genes associated with P profiles, such as Firmicutes, Ignavibacteriota, and P mineralizing genes in the sediment and plastisphere. This, in turn, elevated the levels of soluble reactive P in the porewater by 54.19 % (0-1 cm), 55.81 % (1-3 cm), and 18.24 % (3-5 cm), respectively. Additionally, PLA obviously altered P immobilization capacity and bioavailability, increasing the organic P fraction. Whereas, inert cobblestone exhibited negligible influence on P biogeochemical processes during the incubation. Moreover, the biofilm communities and those in the surrounding sediment specifically contributed to the changes in P profiles at the SWI. The functional genes associated with P profiles in the sediment mainly concentrate on P mineralization and P uptake/transport. In the plastisphere, P activation genes are obviously affected under MP exposure. This study fills the knowledge gap concerning the repercussions of MPs on ecosystem services.

A review focusing on mechanisms and ecological risks of enrichment and propagation of antibiotic resistance genes and mobile genetic elements by microplastic biofilms

Microplastics (MPs) are emerging ubiquitous pollutants in aquatic environment and have received extensive global attention. In addition to the traditional studies related to the toxicity of MPs and their carrier effects, their unique surface-induced biofilm formation also increases the ecotoxicity potential of MPs from multiple perspectives. In this review, the ecological risks of MPs biofilms were summarized and assessed in detail from several aspects, including the formation and factors affecting the development of MPs biofilms, the selective enrichment and propagation mechanisms of current pollution status of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in MPs biofilms, the dominant bacterial communities in MPs biofilms, as well as the potential risks of ARGs and MGEs transferring from MPs biofilms to aquatic organisms. On this basis, this paper also put forward the inadequacy and prospects of the current research and revealed that the MGEs-mediated ARG propagation on MPs under actual environmental conditions and the ecological risk of the transmission of ARGs and MGEs to aquatic organisms and human beings are hot spots for future research. Relevant research from the perspective of MPs biofilm should be carried out as soon as possible to provide support for the ecological pollution prevention and control of MPs.

Biofilm of petroleum-based and bio-based microplastics in seawater in response to Zn(II): Biofilm formation, community structure, and microbial function

Microplastic biofilms are novel vectors for the transport and spread of pathogenic and drug-resistant bacteria. With the increasing use of bio-based plastics, there is an urgent need to investigate the microbial colonization characteristics of these materials in seawater, particularly in comparison with conventional petroleum-based plastics. Furthermore, the effect of co-occurring contaminants, such as heavy metals, on the formation of microplastic biofilms and bacterial communities remains unclear. In this study, we compared the biofilm bacterial community structure of petroleum-based polyethylene (PE) and bio-based polylactic acid (PLA) in seawater under the influence of zinc ions (Zn2+). Our findings indicate that the biofilm on PLA microplastics in the late stage was impeded by the formation of a mildly acidic microenvironment resulting from the hydrolysis of the ester group on PLA. The PE surface had higher bacterial abundance and diversity, with a more intricate symbiotic pattern. The bacterial structures on the two types of microplastics were different; PE was more conducive to the colonization of anaerobic bacteria, whereas PLA was more favorable for the colonization of aerobic and acid-tolerant species. Furthermore, Zn increased the proportion of the dominant genera that could utilize microplastics as a carbon source, such as Alcanivorax and Nitratireductor. PLA had a greater propensity to harbor and disseminate pathogenic and drug-resistant bacteria, and Zn promoted the enrichment and spread of harmful bacteria such as, Pseudomonas and Clostridioides. Therefore, further research is essential to fully understand the potential environmental effects of bio-based microplastics and the role of heavy metals in the dynamics of bacterial colonization.

Myco-remediation of plastic pollution: current knowledge and future prospects

To date, enumerable fungi have been reported to participate in the biodegradation of several notorious plastic materials following their isolation from soil of plastic-dumping sites, marine water, waste of mulch films, landfills, plant parts and gut of wax moth. The general mechanism begins with formation of hydrophobin and biofilm proceding to secretion of specific plastic degarding enzymes (peroxidase, hydrolase, protease and urease), penetration of three dimensional substrates and mineralization of plastic polymers into harmless products. As a result, several synthetic polymers including polyethylene, polystyrene, polypropylene, polyvinyl chloride, polyurethane and/or bio-degradable plastics have been validated to deteriorate within months through the action of a wide variety of fungal strains predominantly Ascomycota (Alternaria, Aspergillus, Cladosporium, Fusarium, Penicillium spp.). Understanding the potential and mode of operation of these organisms is thus of prime importance inspiring us to furnish an up to date view on all the presently known fungal strains claimed to mitigate the plastic waste problem. Future research henceforth needs to be directed towards metagenomic approach to distinguish polymer degrading microbial diversity followed by bio-augmentation to build fascinating future of waste disposal.

Recent advances in the relationships between biofilms and microplastics in natural environments

Plastic pollution in the form of microplastics (MPs), poses a significant threat to natural ecosystems, with detrimental ecological, social, and economic impacts. This review paper aims to provide an overview of the existing research on the interaction between microbial biofilms and MPs in natural environments. The review begins by outlining the sources and types of MPs, emphasizing their widespread presence in marine, freshwater, and terrestrial ecosystems. It then discusses the formation and characteristics of microbial biofilms on MPs surfaces, highlighting their role in altering the physicochemical properties of MPs and facilitating processes such as vertical transport, biodegradation, dispersion of microorganisms, and gene transfer. Different methods used to assess these interactions are discussed, including microbiological and physicochemical characterization. Current gaps and challenges in understanding the complex relationships between biofilms and MPs are identified, highlighting the need for further research to elucidate the mechanisms underlying these complex interactions and to develop effective mitigation strategies. Innovative solutions, including bioremediation techniques and their combination with other strategies, such as nanotechnology, advanced filtration technologies, and public awareness campaigns, are proposed as promising approaches to address the issue of MPs pollution. Overall, this review underscores the urgent need for a multidisciplinary approach to combating MPs pollution, combining scientific research, technological innovation, and public engagement to safeguard the health and integrity of natural ecosystems.

Effects of microplastics on the structure and function of bacterial communities in sediments of a freshwater lake

As an emerging pollutant, microplastics (MPs) cause widespread concern around the world owing to the serious threat they pose to ecosystems. In particular, sediments are thought to be the long-term sink for the continual accumulation of MPs in freshwater ecosystems. Polyethylene (PE) and polyethylene terephthalate (PET) have been frequently detected with large concentration variations in freshwater sediments from the lower reaches of the Yangtze River, one of the most economically developed regions in China, characterized by accelerated urbanization and industrialization, high population density and high plastics consumption. However, the impact of PE and PET on the sedimental bacterial community composition and its function has not been well reported for this specific region. Herein, PE and PET particles were added to freshwater sediments to assess the effects of different MP types on the bacterial community and its function, using three concentrations (500, 1500 and 2500 items/kg) per MP and incubations of 35, 105 and 175 days, respectively. This study identified a total of 68 phyla, 211 classes, 518 orders, 853 families and 1745 genera. Specifically, Proteobacteria, Chloroflexi, Acidobacteriota, Actinobacteriota and Firmicutes were the top five phyla. A higher bacterial diversity was obtained in control sediments than in the MP-treated sediments. The presence of MPs, whether PET or PE, had significant impact on the bacterial diversity, community structure and community composition. PICRUSt2 and FAPOTAX predictions demonstrated that MPs could potentially affect the metabolic pathways and ecologically functional groups of bacteria in the sediment. Besides the MP-related factors, such as the type, concentration and incubation time, the physicochemical parameters had an effect on the structure and function of the bacterial community in the freshwater sediment. Taken together, this study provides useful information for further understanding how MPs affect bacterial communities in the freshwater sediment of the lower reaches of the Yangtze River, China.

Freshwater plastisphere: a review on biodiversity, risks, and biodegradation potential with implications for the aquatic ecosystem health

The plastisphere, a unique microbial biofilm community colonizing plastic debris and microplastics (MPs) in aquatic environments, has attracted increasing attention owing to its ecological and public health implications. This review consolidates current state of knowledge on freshwater plastisphere, focussing on its biodiversity, community assembly, and interactions with environmental factors. Current biomolecular approaches revealed a variety of prokaryotic and eukaryotic taxa associated with plastic surfaces. Despite their ecological importance, the presence of potentially pathogenic bacteria and mobile genetic elements (i.e., antibiotic resistance genes) raises concerns for ecosystem and human health. However, the extent of these risks and their implications remain unclear. Advanced sequencing technologies are promising for elucidating the functions of plastisphere, particularly in plastic biodegradation processes. Overall, this review emphasizes the need for comprehensive studies to understand plastisphere dynamics in freshwater and to support effective management strategies to mitigate the impact of plastic pollution on freshwater resources.

Exploring correlations between microplastics, microorganisms, and water quality in an urban drinking water source

The microplastic pollution in freshwater system is gradually becoming more severe, which has led to increasing attention on the distribution and potential harmful effects of microplastics. Moreover, microplastics may have an impact on river ecology and pose risks to ecosystems. Therefore, it is important to reveal this process. This study aimed to explore correlations between microplastics and free-living microorganisms in an urban drinking water source of Xiangjiang River by using multivariate statistical analysis. The results indicated that the abundance of microplastics (size 50 μm to 5 mm) in surface water and sediments ranged from 0.72 to 18.6 (mean ± SD: 7.32 ± 2.36) items L-1 and 26.3-302 (150 ± 75.6) items kg-1 dry weight (dw), respectively, suggesting potential microplastic pollution despite the protected status as a drinking water source. Higher microplastic abundances were observed in urban areas and the downstream of wastewater plants, with mostly granular shape, transparent and black color as well as 50-100 μm in size. The multivariate statistical analysis presented that the abundance of microplastics is not significantly correlated with water indicators, due to the complexity of the abundance data. The water indicators showed an obvious correlation with microplastics in colors of transparent and black, and smaller sizes of 50-100 μm. This is also true for microplastics and microorganisms in water and sediment. Proteobacteria was the main prokaryote in water and sediments, being positively correlated with 50-100 μm microplastics; while Chloroplastida was the dominated eukaryotes, presenting a weak correlation with smaller-size microplastics. Overall, when considering the properties of microplastics such as shape, color and size, the potential correlations with water indicators and microorganisms were more evident than abundance. This study provides new insights into the multivariate statistical analysis, explaining the potential correlations among microplastic properties, microorganisms and environmental factors in a river system.

Revealing the characteristics of biofilms on different polypropylene plastic products: Comparison between disposable masks and takeaway boxes

The increasingly severe plastic pollution issue was intensified by the enormous plastic emissions into ecosystems during the Covid-19 pandemic. Plastic wastes entering the environment were swiftly exposed to microorganisms and colonized by biofilms, and the plastic-biofilm combined effects further influenced the ecosystem. However, the non-woven structure of disposable masks discarded carelessly during the COVID-19 pandemic was different from those of plastics with flat surface. To reveal the potential effects of plastic structure on colonized biofilms, white disposable surgical masks (DM) and transparent takeaway boxes (TB), both made of polyethylene, were selected for the incubation of organic conditioning films and biofilms. The results indicated that the non-woven structure of disposable mask was destroyed by the influence of water infiltration and biofilm colonization. The influence of surface structure on conditioning films led to a relatively higher proportion of tryptophan-like substances on DM than those on TB samples. Therefore, biofilms with significantly higher microbial biomass and carbon metabolic capacity were formed on DM than those on TB samples owing to the combined effects of their differences in surface structure and conditioning films. Moreover, abundant functional microorganisms associated with stress tolerance, carbon metabolism and biofilm formation were observed in biofilms on disposable mask. Combining with the results of partial least squares regression analysis, the selective colonization of functional microorganisms on disposable masks with uneven surface longitudinal fluctuation was revealed. Although the predicted functions of biofilms on disposable masks and takeaway boxes showed more similarity to each other than to those of free-living aquatic microorganisms owing to the existence of the plastisphere, biofilms on disposable masks may potentially trigger environmental risks different from those of takeaway boxes by unique carbon metabolism and abundant biomass.

Farmland Microhabitat Mediated by a Residual Microplastic Film: Microbial Communities and Function

How the plastisphere mediated by the residual microplastic film in farmlands affects microhabitat systems is unclear. Here, microbial structure, assembly, and biogeochemical cycling in the plastisphere and soil in 33 typical farmland sites were analyzed by amplicon sequencing of 16S rRNA genes and ITS and metagenome analysis. The results indicated that residual microplastic film was colonized by microbes, forming a unique niche called the plastisphere. Notable differences in the microbial community structure and function were observed between soil and plastisphere. Residual microplastic film altered the microbial symbiosis and assembly processes. Stochastic processes significantly dominated the assembly of the bacterial community in the plastisphere and soil but only in the plastisphere for the fungal community. Deterministic processes significantly dominated the assembly of fungal communities only in soil. Moreover, the plastisphere mediated by the residual microplastic film acted as a preferred vector for pathogens and microorganisms associated with plastic degradation and the nitrogen and sulfur cycle. The abundance of genes associated with denitrification and sulfate reduction activity in the plastisphere was pronouncedly higher than that of soil, which increase the potential risk of nitrogen and sulfur loss. The results will offer a scientific understanding of the harm caused by the residual microplastic film in farmlands.

Temporal dynamics of bacterial colonization on five types of microplastics in a freshwater lake

Microplastics (MPs), as a new substrate, provide a unique niche for microbial colonization in the freshwater ecosystems; however, the impacts of long-term MP exposure on colonized bacteria are still unclear. In this study, five MP types were exposed in a freshwater lake for approximately one year, and the MP particles, together with the surrounding water, were collected on days 60, 150, 250 and 330 during the in situ field experiment. Bacteria on the MP surface, as well as free-living bacteria in the surrounding water, were analyzed to evaluate the temporal dynamics of these bacterial communities. Results show that all five MP types exhibited signs of degradation during the exposure process. Additionally, the alpha diversity, community structure and composition of MP-attached bacteria significantly differed from that of the free-living bacteria in the surrounding water, indicating that the five MP types could provide a preferable niche for bacterial colonization in a freshwater environment. Proteobacteria, Chloroflexi, Verrucomicrobiota, Actinobacteriota and Firmicutes were the top five dominant phyla. Some plastic-degrading bacteria included in these phyla were detected, verifying that MP-attached biofilms had a certain degree of MP degradation potential. Some potentially pathogenic bacteria were also detected, suggesting an ecological threat for spreading disease in the aquatic ecosystem. Furthermore, the bacterial community and some metabolic pathways were significantly affected by the MP type (P < 0.01) and exposure time (P < 0.01), indicating that the presence of MPs not only alters the bacterial community structure and composition, but also influences their potential functional properties in freshwater ecosystems. Multiple factors, including the physicochemical properties related to MPs and the environmental parameters of the surrounding water, affect the community composition and the function of MP-attached bacteria to different degrees. Our findings indicate that the presence of MPs has a potential ecological impact on freshwater ecosystems.

The antioxidant strain Lactiplantibacillus plantarum AS21 and Clostridium butyricum ameliorate DSS-induced colitis in mice by remodeling the assembly of intestinal microbiota and improving gut functions

Probiotics are known for their beneficial effects on improving intestinal function by alleviating the gut microbial diversity. However, the influences of antioxidant lactic acid bacteria (LAB) and anti-inflammatory Clostridium butyricum (CB) on ameliorating enteritis remain unclear. In this study, we investigated the effects of the antioxidant strain Lactiplantibacillus plantarum AS21 and CB alone, or in combination on intestinal microbiota, barrier function, oxidative stress and inflammation in mice with DSS-induced colitis. All probiotic treatments relieved the pathological development of colitis by improving the integrity of the intestinal mucosal barrier and the length of the colon. The probiotics also suppressed inflammation and oxidative stress by improving gut short-chain fatty acids and inhibiting the p38-MAPK/NF-κB pathway in colon tissues. According to the meta-network analysis, three distinct modules containing sensitive OTUs of the gut bacterial community specific to the control, DSS and DSS + probiotics groups were observed, and unlike the other two modules, Lachnospiraceae and Clostridia dominated the sensitive OTUs in the DSS + probiotics group. In addition, administration of the present probiotics particularly increased antioxidant and anti-inflammatory microbes Muribaculaceae, Bifidobacterium, Prevotellaceae and Alloprevotella. Furthermore, combined probiotic strain treatment showed a more stable anti-colitis effect than a single probiotic strain. Collectively, the present probiotics exhibited protective effects against colitis by suppressing the inflammation and oxidative damage in the colon, improving the gut microbiota and their functions, and consequently preventing the gut leak. The results indicate that the combination of the antioxidant properties of LAB and the anti-inflammatory properties of CB as nutritional intervention and adjuvant therapy could be an effective strategy to prevent and alleviate colitis.

Organic matter stability and lability in terrestrial and aquatic ecosystems: A chemical and microbial perspective

Terrestrial and aquatic ecosystems have specific carbon fingerprints and sequestration potential, due to the intrinsic properties of the organic matter (OM), mineral content, environmental conditions, and microbial community composition and functions. A small variation in the OM pool can imbalance the carbon dynamics that ultimately affect the climate and functionality of each ecosystem, at regional and global scales. Here, we review the factors that continuously contribute to carbon stability and lability, with particular attention to the OM formation and nature, as well as the microbial activities that drive OM aggregation, degradation and eventually greenhouse gas emissions. We identified that in both aquatic and terrestrial ecosystems, microbial attributes (i.e., carbon metabolism, carbon use efficiency, necromass, enzymatic activities) play a pivotal role in transforming the carbon stock and yet they are far from being completely characterised and not often included in carbon estimations. Therefore, future research must focus on the integration of microbial components into carbon mapping and models, as well as on translating molecular-scaled studies into practical approaches. These strategies will improve carbon management and restoration across ecosystems and contribute to overcome current climate challenges.

The effect of polyvinyl chloride (PVC) color on biofilm development and biofilm-heavy metal chemodynamics in the aquatic environment

Plastic surfaces are colonized by microorganisms and biofilms are formed in the natural aquatic environment. As the biofilm develops, it changes the density and buoyancy of the plastic-biofilm complex, results in plastic sinking, and increases the heavy metals accumulated by biofilm's mobility and availability in aquatic ecosystems. In this experiment, biofilms were cultured on five colors of polyvinyl chloride (PVC; transparent, green, blue, red, black) in an aquatic environment to investigate the effects of plastic color on biofilm formation and development (Phase 1) and to study the effects of being sunk below the photic zone on biofilm (Phase 2). The PVC color significantly affected the biofilm formation rate but had no impact on the final biofilm biomass. After sinking the biofilm-PVC below the photic zone in Phase 2, the layer of diatoms on the biofilm surface began to disintegrate, and the biomass and Chlorophyll-a (Chla) content of the biofilm decreased, except on the red PVC. Below the photic zone, the microbial community of the biofilm changed from primarily autotrophic microbes to mostly heterotrophic microbes. Microbial diversity increased and extracellular polymeric substances (EPS) content decreased. The primary factor leading to microbial diversity and community structure changes was water depth rather than PVC color. The changes induced in the biofilm led to an increase in the concentration of all heavy metals in the biofilm, related to the increase in microbial diversity. This study provides new insights into the biofilm formation process and the effects on a biofilm when it sinks below the photic zone.

Exposure to three herbicide mixtures influenced maize root-associated microbial community structure, function and the network complexity

Herbicide mixtures are a new and effective agricultural strategy for managing suppress weed resistance and have been widely used in controlling weeding growth in maize fields. However, the potential ecotoxicological impact of these mixtures on the microbial community structure and function within various root-associated niches, remains inadequately understood. Here, the effects of nicosulfuron, mesotrione and atrazine on soil enzyme activity and microbial community structure and function were investigated when applied alone and in combination. The findings indicated that herbicide mixtures exhibit a prolonged half-life compared to single herbicides. Ecological niches are the major factor influencing the structure and functions of the microbial community, with the rhizosphere exhibiting a more intensive response to herbicide stress. Herbicides significantly inhibited the activities of soil functional enzymes, including dehydrogenase, urease and sucrose in the short-term. Single herbicide did not drastically influence the alpha or beta diversity of the soil bacterial community, but herbicide mixtures significantly increased the richness of the fungal community. Meanwhile, the key functional microbial populations, such as Pseudomonas and Enterobacteriaceae, were significantly altered by herbicide stress. Both individual and combined use of the three herbicides reduced the complexity and stability of the bacterial network but increased the interspecific cooperations of fungal community in the rhizosphere. Moreover, by quantification of residual herbicide concentrations in the soil, we showed that the degradation period of the herbicide mixture was longer than that of single herbicides. Herbicide mixtures increased the contents of NO3--N and NH4+-N in the soil in the short-term. Overall, our study provided a comprehensive insight into the response of maize root-associated microbial communities to herbicide mixtures and facilitated the assessment of the ecological risks posed by herbicide mixtures to the agricultural environment from an agricultural sustainability perspective.

Unveiling novel perspectives on niche differentiation and plasticity in rhizosphere phosphorus forms of submerged macrophytes with different stoichiometric homeostasis

Stoichiometric homeostasis is the ability of organisms to maintain their element composition through various physiological mechanisms, regardless of changes in nutrient availability. Phosphorus (P) is a critical limiting element for eutrophication. Submerged macrophytes with different stoichiometric homeostasis regulated sediment P pollution by nutrient resorption, but whether and how P homeostasis and resorption in submerged macrophytes changed under variable plant community structure was unclear. Increasing evidence suggests that rhizosphere microbes drive niche overlap and differentiation for different P forms to constitute submerged macrophyte community structure. However, a greater understanding of how this occurs is required. This study examined the process underlying the metabolism of different rhizosphere P forms of submerged macrophytes under different cultivation patterns by analyzing physicochemical data, basic plant traits, microbial communities, and transcriptomics. The results indicate that alkaline phosphatase serves as a key factor in revealing the existence of a link between plant traits (path coefficient = 0.335, p < 0.05) and interactions with rhizosphere microbial communities (average path coefficient = 0.362, p < 0.05). Moreover, this study demonstrates that microbial communities further influence the niche plasticity of P by mediating plant root P metabolism genes (path coefficient = 0.354, p < 0.05) and rhizosphere microbial phosphorus storage (average path coefficient = 0.605, p < 0.01). This research not only contributes to a deeper comprehension of stoichiometric homeostasis and nutrient dynamics but also provides valuable insights into potential strategies for managing and restoring submerged macrophyte-dominated ecosystems in the face of changing nutrient conditions.

Microplastics enrichment characteristics of antibiotic resistance genes and pathogens in landfill leachate

Microplastics (MPs) pollution is a pressing environmental issue for aquatic ecosystems. Landfill leachate is an important contributor of MPs and antibiotic resistant genes (ARGs). However, there are few studies on the colonization of ARGs and pathogens on MPs in leachate. This study conducted incubation experiments with polyethylene terephthalate (PET) and polypropylene (PP) MPs in landfill leachate which were about 3-5 years old (PL) and 5-10 years old (AL). After incubation, the bacterial cells colonized and grew on the surface of MPs, inducing the increase of oxygenated oxygen functional groups (e.g., hydroxyl, carbonyl) on the MPs surface. Real-time PCR indicated that MPs selectively enriched ARGs, such as genes tetM, tetC, mcr-1, aac(6')-Ib-cr, blaTEM and blaSHV in leachate. The diversity of bacterial communities on MPs was significantly increased in AL leachate, but decreased in PL leachate. The differences in bacterial communities in MPs biofilms were related to the type of MPs. Compared with AL leachate, the abundance of Chloroflexi increased by 15.7% on the PET, and the abundance of Acidobacteriota increased by 6.23 fold on the PP. The abundance of Firmicutes increased from 20.7% in PL leachate to 65.8% and 60.7% on PET and PP, respectively. Additionally, pathogens were observed to be more abundant on MPs compared to leachate. In particular, pathogens (Staphylococcus, Streptococcus, Enterobacter and Rhodococcus) associated with sul1 and sul2 were generally present at higher levels on MPs than in the surrounding leachate. These results provide significant implications for understanding the health risk of MPs in the environment.

Wood decay fungi show enhanced biodeterioration of low-density polyethylene in the absence of wood in culture media

The involvement of microorganisms in low-density polyethylene (LDPE) degradation is widely studied across the globe. Even though soil, landfills, and garbage dumps are reported to be promising niches for such organisms, recently the involvement of wood decay fungi in polyethylene degradation is highlighted. In light of this, 50 fungal samples isolated from decaying hardwoods were assessed for their wood degradation ability and for their depolymerization enzymatic activities. For the LDPE deterioration assay, 22 fungal isolates having wood decay ability and de-polymerization enzymatic activities were selected. Fungal cultures with LDPE sheets (2 cm x 10 cm x 37.5 μm) were incubated in the presence and in the absence of wood as the carbon source (C) for 45 days. Degradation was measured by weight loss, changes in tensile properties, reduction in contact angle, changes of functional groups in Fourier-transform infrared spectroscopy, Scanning electron microscopic imaging, and CO2 evolution by strum test. Among the isolates incubated in the absence of wood, Phlebiopsis flavidoalba out-performed the other fungal species showing the highest percentage of weight reduction (23.68 ± 0.34%), and the lowest contact angle (64.28° ± 5.01). Biodegradation of LDPE by P. flavidoalba was further supported by 46.79 ± 0.67% of the mass loss, and 3.07 ± 0.13% of CO2 emission (mg/L) in the strum test. The most striking feature of the experiment was that all the isolates showed elevated degradation of LDPE in the absence of wood than that in the presence of wood. It is clear that in the absence of a preferred C source, wood decay fungi thrive to utilize any available C source (LDPE in this case) showing the metabolic adaptability of fungi to survive under stressful conditions. A potential mechanism for LDPE degradation is also proposed.

Distribution and potential ecological risks of microplastics in Zhushan Bay, China

The interaction between microplastics (MPs) and microorganisms may alter the distribution of antibiotic resistance genes (ARGs) in water and increase the ecological risk of drinking water sources. To investigate the characteristics of MPs geographical distribution and its potential ecological risk in typical urban water, this study was conducted in Zhushan Bay, and we carried out a combination of tests to analyze the distribution of MPs and the migration changes of their surface microbial community composition and ARGs in different media by 16S rRNA gene high-throughput sequencing, non-targeted metabolomics and qPCR genomics in the near-shore (I), middle area (Ⅱ) and near-lake (Ⅲ) of Zhushan Bay. The results showed that MPs in fibrous form were dominant in the aquatic environment of Zhushan Bay; Polyurethane (PU) and Silicone were the main MPs types in Zhushan Bay. The abundance of MPs in the water of Zhushan Bay was winter > summer > autumn > spring; and in the sediment was winter > summer > autumn > spring, respectively. The distribution results of MPs in geographical location are as follows: In the water I > Ⅱ > Ⅲ, sediment exhibited Ⅱ > Ⅲ > I. The results indicate that physicochemical factors will affect the geographical distribution of MPs and their surface microbial community composition in the aquatic environment of Zhushan Bay. More cooperative behaviors and increased metabolically important pathways occurred in the microbial network on water-MPs compared to sediment-MPs. However, the microbial community in the sediment-MPs was more stable and had higher abundance of mobile genetic elements (MGEs). A total of 362 differential metabolites were detected, of which 193 were up-regulated and 19 down-regulated differential metabolites. blaTEM, Sul, and inti1 were prevalent in both the water and sediments of Zhushan Bay. Sul1 was most contaminated in ARGs. This study provides the latest field data and insights into MPs pollution in key aquatic environments.

Life on bottles: Colonisation of macroplastics by freshwater biota

While rivers are known to be the main vectors of plastics to the sea, it seems surprising that studies on interactions (e.g. colonisation/entrapment and drift) between macroplastics and biota continue to remain largely neglected, notwithstanding they represent unexpected threats to freshwater biota and riverine habitats. To fill these gaps, here we focused on the colonisation of plastic bottles by freshwater biota. To do so, we collected 100 plastic bottles from the River Tiber in summer 2021. Overall, 95 bottles were colonised externally and 23 internally. Specifically, biota mainly occurred within and outside the bottles rather than plastic pieces and organic debris. Moreover, while bottles were externally covered mainly by vegetal organisms (i.e. macrophytes), they internally entrapped more animal organisms (i.e. invertebrates). The taxa most occurring within and outside the bottles belonged to pool and low water quality-associated taxa (e.g. Lemna sp., Gastropoda, and Diptera). In addition to biota and organic debris, plastic particles also occurred on bottles reporting the first observation of 'metaplastics' (i.e. plastics encrusted on bottles). Furthermore, we observed a significant positive correlation between the colonising taxa abundance and the bottle degree degradation. In this regard, we discussed how bottle buoyancy may change due to the organic matter on the bottle, affecting bottle sinking and transport along rivers. Our findings might be crucial for understanding the underrepresented topic of riverine plastics and their colonisation by biota, given that these plastics may act as vectors and cause biogeographical, environmental, and conservation issues to freshwater habitats.

Effects of bioaugmentation by isolated Achromobacter xylosoxidans BP1 on PAHs degradation and microbial community in contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic pollutants ubiquitous and persistent in soil. In order to provide a viable solution for bioremediation of PAHs-contaminated soil, a strain of Achromobacter xylosoxidans BP1 with superior PAHs degradation ability was isolated from contaminated soil at a coal chemical site in northern China. The degradation of phenanthrene (PHE) and benzo[a]pyrene (BaP) by strain BP1 was investigated in three different liquid phase cultures, and the removal rates of PHE and BaP by strain BP1 were 98.47% and 29.86% after 7 days under the conditions of PHE and BaP as the only carbon source, respectively. In the medium with the coexistence of PHE and BaP, the removal rates of BP1 were 89.44% and 9.42% after 7 days, respectively. Then, strain BP1 was investigated for its feasibility in remediating PAH-contaminated soil. Among the four PAHs-contaminated soils treated differently, the treatment inoculated with BP1 exhibited higher removal rates of PHE and BaP (p < 0.05), especially the CS-BP1 treatment (inoculation of BP1 into unsterilized PAHs-contaminated soil) showed 67.72%, 13.48% removal of PHE and BaP, respectively, over 49 days of incubation. Bioaugmentation also significantly increased the activity of dehydrogenase and catalase in the soil (p＜0.05). Furthermore, the effect of bioaugmentation on the removal of PAHs was investigated by measuring the activity of dehydrogenase (DH) and catalase (CAT) during incubation. Among them, the DH and CAT activities of CS-BP1 and SCS-BP1 (inoculation of BP1 into sterilized PAHs-contaminated soil) treatments inoculated with strain BP1 were significantly higher than those of treatments without BP1 addition during incubation (p < 0.01). The structure of the microbial community varied among treatments, but the Proteobacteria phylum showed the highest relative abundance in all treatments of the bioremediation process, and most of the bacteria with higher relative abundance at the genus level also belonged to the Proteobacteria phylum. Prediction of microbial functions in soil by FAPROTAX analysis showed that bioaugmentation enhanced microbial functions associated with the degradation of PAHs. These results demonstrate the effectiveness of Achromobacter xylosoxidans BP1 as a PAH-contaminated soil degrader for the risk control of PAHs contamination.

A plastic world: A review of microplastic pollution in the freshwaters of the Earth's poles

Microplastic (MP) pollution is of great environmental concern. MPs have been found all over the Earth, including in the poles, which is indicative for the important threat they constitute. Yet, while the ocean is object of major interest, the data available in the literature about MP pollution in the freshwaters of the Earth's poles are still limited. Here, we review the current knowledge of MP pollution in the freshwaters of the Arctic, Antarctica and Third Pole, and we assess its ecological implications. This review highlights the presence of MPs in the lakes, rivers, snow, and glaciers of the investigated sites, questions the transport patterns through which MPs reach these remote areas, and illustrates that MP pollution is a real problem not only in marine systems, but also in the freshwater environments of the Earth's poles. MPs can indeed be ingested by animals and can physically damage their digestive tracts, as well as escalate the trophic levels. MPs can also alter microbial communities by serving as surfaces onto which microbes can grow and develop, and can enhance ice melting when trapped in glaciers. Hence, considered the limited data available, we encourage more research on the theme.

Aquatic plastisphere: Interactions between plastics and biofilms

Because of the high production rates, low recycling rates, and poor waste management of plastics, an increasing amount of plastic is entering the aquatic environment, where it can provide new ecological niches for microbial communities and form a so-called plastisphere. Recent studies have focused on the one-way impact of plastic substrata or biofilm communities. However, our understanding of the two-way interactions between plastics and biofilms is still limited. This review first summarizes the formation process and the co-occurrence network analysis of the aquatic plastisphere to comprehensively illustrate the succession pattern of biofilm communities and the potential consistency between keystone taxa and specific environmental behavior of the plastisphere. Furthermore, this review sheds light on mutual interactions between plastics and biofilms. Plastic properties, environmental conditions, and colonization time affect biofilm development. Meanwhile, the biofilm communities, in turn, influence the environmental behaviors of plastics, including transport, contaminant accumulation, and especially the fragmentation and degradation of plastics. Based on a systematic literature review and cross-referencing from these disciplines, the current research focus, and future challenges in exploring aquatic plastisphere development and biofilm-plastic interactions are proposed.

Characterization of microbial community, ecological functions and antibiotic resistance in estuarine plastisphere

The plastisphere is a new ecological niche. Compared to the surrounding water, microbial community composition associated with the plastisphere is known to differ with functional consequences. Here, this study characterized the bacterial and fungal communities associated with four types of plastisphere (polyethylene, polystyrene, polypropylene and polyvinyl chloride) in an estuarine habitat; assessed ecological functions including carbon, nitrogen, phosphorus and sulfur cycling, and determined the presence of antibiotic resistance genes (ARGs) and human pathogens. Stochastic processes dominated the community assembly of microorganisms on the plastisphere. Several functional genera related to nutrient cycling were enriched in the plastisphere. Compared to surrounding water and other plastisphere, the abundances of carbon, nitrogen and phosphorus cycling genes (cdaR, nosZ and chpy etc.) and ARGs (aadA2-1, cfa and catB8 etc.) were significantly increased in polyvinyl chloride plastisphere. In contrast, the polystyrene plastisphere was the preferred substrate for several pathogens being enriched with for example, Giardia lamblia 18S rRNA, Klebsiella pneumoniae phoE and Legionella spp. 23S rRNA. Overall, this study showed that different plastisphere had different effects on ecological functions and health risk in estuaries and emphasizes the importance of controlling plastic pollution in estuaries. Data from this study support global policy drivers that seek to reduce plastic pollution and offer insights into ecological functions in a new ecological niche of the Anthropocene.

Atrazine sorption on biodegradable microplastics: Significance of microbial aging

The study of the environmental sorption behavior of typical biodegradable microplastics (BMPs) during biodegradation is essential given the different characteristics of BMPs and conventional microplastics (MPs) and the knowledge gap on the sorption capacity of BMPs for pollutants during degradation. In this study, polylactic acid (PLA) and poly (butylene-adipate-co-terephthalate) (PBAT) were chosen as research objects, and the effects of soil microbial aging on their surface properties and atrazine (ATZ) sorption were investigated. The structural composition of the bacterial community was essentially similar between B-PLA and B-PBAT. Microbial aging action created new pores and cavities in PLA, forming microbial films that led to the agglomeration of PLA particles. The microbial aging action destroyed the amorphous regions of PLA and PBAT, resulting in higher crystallinity, and the ester groups broke to form carboxyl groups. The equilibrium sorption (Q_e) of B-PLA increased by 11.12 % compared with PLA, while the Q_e of B-PBAT decreased by 4.95 % compared to PBAT. These results show that soil microbes change the surface properties of PLA and PBAT, thus affecting the sorption mechanism of ATZ, and provide a theoretical premise for the behavior and ecological risk assessment of ATZ in the presence of BMPs.

Artificial substrata to assess ecological and ecotoxicological responses in river biofilms: Use and recommendations

River biofilms are biological consortia of autotrophs and heterotrophs colonizing most solid surfaces in rivers. Biofilm composition and biomass differ according to the environmental conditions, having different characteristics between systems and even between river habitats. Artificial substrata (AS) are an alternative for in situ or laboratory experiments to handle the natural variability of biofilms. However, specific research goals may require decisions on colonization time or type of substrata. Substrata properties (i.e., texture, roughness, hydrophobicity) and the colonization period and site are selective factors of biofilm characteristics. Here we describe the uses of artificial substrata in the assessment of ecological and ecotoxicological responses and propose a decision tree for the best use of artificial substrata in river biofilm studies. We propose departing from the purpose of the study to define the necessity of obtaining a realistic biofilm community, from which it may be defined the colonization time, the colonization site, and the type of artificial substratum. Having a simple or mature biofilm community should guide our decisions on the colonization time and type of substrata to be selected for the best use of AS in biofilm studies. Tests involving contaminants should avoid adsorbing materials while those ecologically oriented may use any AS mimicking those substrata occurring in the streambed.•We review the utilization of different artificial substrata to colonize biofilm in river ecology and ecotoxicology.•We propose a decision tree to guide on selecting the appropriate artificial substrata and colonization site and duration.•Type of artificial substrata (material, size, shape...) and colonization duration are to be decided according to the specific purpose of the study.

Microplastics drive nitrification by enriching functional microorganisms in aquaculture pond waters

The plastisphere refers to biofilm formation on the microplastic (MP) surface, but its subsequent functions, especially driving the nitrogen biogeochemical cycle, are rarely studied. Here, MPs were incubated in the pelagic water and benthic water-sediment interface of an aquaculture pond, and the two corresponding microcosms amended with incubated plastisphere were simulated. The results showed decreased ammonia concentrations and increased nitrification rates in microcosms with either pelagic or benthic plastispheres. To uncover the possible mechanisms, the community structure and function of the plastisphere were investigated. As clarified by 16S rRNA, the community diversity of the pelagic plastisphere was significantly higher than that of the corresponding hydrosphere. Plastisphere communities, especially those incubated in pelagic water, were separated from the hydrosphere. Moreover, the abundance of Proteobacteria increased while the abundance of Cyanobacteria decreased in both plastispheres. Metagenome further revealed that the abundance of amoA and annotated Nitrososphaeraceae_archaeon and hao and affiliated Nitrosomonas_europaea, which contributed to ammonia oxidation to nitrite, was higher in the benthic plastisphere. Comparing the pelagic plastisphere with the corresponding hydrosphere, however, the abundance of nxrA and annotated Nitrobacter hamburgensis and nxrB and the affiliated Nitrospira moscoviensis, which are involved in nitrite oxidation, was more abundant in the plastisphere. These findings suggest that the plastisphere might selectively enrich functional microorganisms and genes in a habitat-dependent manner to promote nitrification in aquaculture ponds.

Microbial community niches on microplastics and prioritized environmental factors under various urban riverine conditions

Microplastics (MPs) provide habitats to microorganisms in aquatic environments; distinct microbial niches have recently been elucidated. However, there is little known about the microbial communities on MPs under urban riverine conditions, in which environmental factors fluctuate. Therefore, this study investigated MP biofilm communities under various urban riverine conditions (i.e., organic content, salinity, and dissolved oxygen (DO) concentration) and evaluated the prioritized factors affecting plastisphere communities. Nine biofilm-forming reactors were operated under various environmental conditions. Under all testing conditions, biofilms grew on MPs with decreasing bacterial diversity. Interestingly, biofilm morphology and bacterial populations were driven by the environmental parameters. We found that plastisphere community structures were grouped according to the environmental conditions; organic content in the water was the most significant factor determining MP biofilm communities, followed by salinity and DO concentration. The principal plastisphere communities were Proteobacteria, Bacteroidetes, Cyanobacteria, and Firmicutes phyla. In-depth analyses of plastisphere communities revealed that biofilm-forming and plastic-degrading bacteria were the predominant microbes. In addition, potential pathogens were majorly discovered in the riverine waters with high organic content. Our results suggest that distinct plastisphere communities coexist with MP particles under certain riverine water conditions, implying that the varied MP biofilm communities may affect urban riverine ecology in a variety of ways.

Plastic microbiome development in a freshwater ecosystem

To understand biological interactions of plastic litter in freshwater ecosystems, as well the potential effects of plastics on ecosystem processes, studies of the activity and composition of plastic-associated microbial communities are needed. The physical properties and chemical composition of plastic polymers are key components of plastic product design, and may also select for distinct microbial biofilms colonizing plastic litter. We monitored growth and succession of biofilm communities on plastic substrates of common morphotypes (i.e., hard, soft, foam, and film) and a natural surface (i.e., an unglazed ceramic tile) incubated in an urban stream. We measured biofilm biomass, metabolism, extracellular enzyme activity, and bacterial, fungal and algal community composition over four weeks during primary succession. Results demonstrated a general increase in biofilm biomass and enzymatic activity corresponding to carbon, nitrogen and phosphorus metabolism during biofilm development for all substrate types. We observed higher respiration rates and negative net ecosystem productivity on foam and tile surfaces in comparison to hard, soft and film plastic surfaces. Biofilm bacterial, fungal and algal assemblages showed few significant differences in composition among substrates. However, all microbial communities changed significantly in composition over time. While substrate type was not the major factor driving biofilm composition and activity, these data show plastic litter in streams is well colonized by an active and dynamic biofilm community. As plastic litter is increasing across all types of aquatic ecosystems, it should be considered a medium for biologically active organisms that contribute to key ecosystem processes.

Biofilm assemblage and activity on plastic in urban streams at a continental scale: Site characteristics are more important than substrate type

The fate of plastics in rivers is a key component of the global plastic cycle. Plastics entering freshwater ecosystems are colonized by microbial biofilms, and microbe-plastic interactions can influence ecosystem processes and plastic fate. While literature examining the role of geographic region on plastic biofilms is quickly expanding, research which covers large (i.e., continental) spatial scales and includes freshwater ecosystems is warranted. In addition, most research focuses on bacterial communities, while biofilm eukaryotes are less commonly studied. We assessed biofilm metabolism and community structure on plastic (foamed polystyrene and polyvinyl chloride; PVC) and natural substrates (unglazed ceramic tile) in urban streams spanning a nested geographic gradient in the continental United States. We measured biofilm biomass, community respiration, and chlorophyll a, in addition to assessing marker gene-based community diversity of bacterial, fungal, and algal assemblages. Results demonstrated some substrate-specific trends in biofilm characteristics, including higher biofilm biomass on polystyrene across sites, and lower diversity of bacterial assemblages on both types of plastic litter versus tile. However, there were no differences among substrates for chlorophyll, respiration, and the abundance and diversity of algal and fungal assemblages. Thus, we concluded that the primary driver of biofilm metabolism and community composition were site characteristics, rather than substrate type. Additional studies are needed to quantify which site-specific characteristics drive biofilm dynamics on plastic litter in streams (e.g., water chemistry, light, seasonality, hydrology). These results add to the growing literature on the biofilm 'plastisphere' in aquatic ecosystems, demonstrating that the factors which control the assembly and activity of biofilm communities on plastic substrates (including bacteria, algal, and fungal assemblages together) in urban streams are similar to those driving biofilm dynamics on natural substrates.

Effects of pyrene on the structure and metabolic function of soil microbial communities

The widely detected pyrene (PYR) is prone to accumulate and pose risks to the soil ecosystem. In this study, an aerobic closed microcosm was constructed to assess the effects of PYR at the environmental concentration (12.09 mg kg^-1) on the structure, interactions, and metabolism of carbon sources of soil microbial communities. The results found that half-life of PYR was 37 d and its aerobic biodegradation was mainly implemented by both Gram-negative and Gram-positive bacteria as revealed by the quantitative results. High-throughput sequencing based on 16 S rRNA and ITS genes showed that PYR exposure interfered more significantly with the diversity and abundance of the bacterial community than that of the fungal community. For bacteria, rare species were sensitive to PYR, while Gemmatimonadota, Gaiellales, and Planococcaceae involved in organic pollutants detoxification and degradation were tolerant of PYR stress. Co-occurrence network analysis demonstrated that PYR enhanced the intraspecific cooperation within the bacterial community and altered the patterns of trophic interaction in the fungal community. Furthermore, the keystone taxa and their topological roles were altered, potentially inducing functionality changes. Function annotation suggested PYR inhibited the nitrogen fixation and ammonia oxidation processes but stimulated methylotrophy and methanol oxidation, especially on day 7. For the metabolism, microbial communities accelerated the metabolism of nitrogenous carbon sources (e.g. amine) to meet the physiological needs under PYR stress. This study clarifies the impacts of PYR on the structure, metabolism, and potential N and C cycling functions of soil microbial communities, deepening the knowledge of the environmental risks of PYR.

Estuarine plastisphere as an overlooked source of N2O production

“Plastisphere”, microbial communities colonizing plastic debris, has sparked global concern for marine ecosystems. Microbiome inhabiting this novel human-made niche has been increasingly characterized; however, whether the plastisphere holds crucial roles in biogeochemical cycling remains largely unknown. Here we evaluate the potential of plastisphere in biotic and abiotic denitrification and nitrous oxide (N₂O) production in estuaries. Biofilm formation provides anoxic conditions favoring denitrifiers. Comparing with surrounding bulk water, plastisphere exhibits a higher denitrifying activity and N₂O production, suggesting an overlooked N₂O source. Regardless of plastisphere and bulk water, bacterial and fungal denitrifications are the main regulators for N₂O production instead of chemodenitrification. However, the contributions of bacteria and fungi in the plastisphere are different from those in bulk water, indicating a distinct N₂O production pattern in the plastisphere. These findings pinpoint plastisphere as a N₂O source, and provide insights into roles of the new biotope in biogeochemical cycling in the Anthropocene.

The roles of marine plastisphere in global nitrogen cycling are largely unknown. Here, the authors indicate that the plastisphere could act as a potential source of N2O production, which is mainly regulated by the biotic denitrification

Community structure and co-occurrence network analysis of bacteria and fungi in wheat fields vs fruit orchards

Soil microorganisms play a vital role in biogeochemical processes and nutrient turnover in agricultural ecosystems. However, the information on how the structure and co-occurrence patterns of microbial communities response to the change of planting methods is still limited. In this study, a total of 34 soil samples were collected from 17 different fields of 2 planting types (wheat and orchards) along the Taige Canal in Yangtze River Delta. The structure of bacterial and fungal communities in soil were determined by 16S rRNA gene and ITS gene, respectively. The dominated bacteria were Proteobacteria, Acidobacteriota, Actinobacteriota, Chloroflexi, Bacteroidota, and Firmicutes. The relative abundances of Actinobacteriota and Firmicutes were higher in the orchards, while Chloroflexi and Nitrospirota were more abundant in wheat fields. Ascomycota, Mortierellomycota, and Basidiomycota were the predominant fungus in both soil types. Diversity of bacterial and fungal communities were greater in the wheat fields than in orchards. Statistical analyses showed that pH was the main factor shaping the community structure, and parameters of water content (WC), total organic carbon (TOC) and total nitrogen (TN) had great influences on community structure. Moreover, high co-occurrence patterns of bacterial and fungal were confirmed in both wheat fields and orchards. Network analyses showed that both wheat fields and orchards occurred modular structure, including nodes of Acidobacteriota, Chloroflexi, Gemmatimonadota, Nitrospirota and Ascomycota. In summary, our work showed the co-occurrence network and the convergence/divergence of microbial community structure in wheat fields and orchards, giving a comprehensive understanding of the microbe-microbe interaction during planting methods' changes.

Effect of particle size on the colonization of biofilms and the potential of biofilm-covered microplastics as metal carriers

Upon release into the aquatic environment, the surface of microplastics (MPs) can be readily colonized by biofilms, which may enhance the adsorption of contaminants. In this study, industrial-grade polystyrene (PS) of about 4 mm in size (MP4000-1), food-grade PS of about 4 mm in size (MP4000-2), and Powder PS of about 75 μm in size (MP75) were co-cultured with a model freshwater fungus, namely Acremonium strictum strain KR21-2, for seven days to form biofilms on their surface. We also determined the changes in surface physicochemical properties of the biofilm-covered MPs (BMPs) and the heavy metal adsorption capacity of the original MPs and BMPs. The results revealed that the biofilms improve the adsorption of heavy metals on MPs, and the particle size of MPs plays a crucial role in biofilm colonization and adsorption of heavy metals by BMPs. MP75 can carry more biofilm on its surface than that of the two MP4000s and form heteroaggregates with biofilms. In addition, there were more functional groups on the surface of BMP75 than on the surface of the two BMP4000s, which could promote the electrostatic interaction and chemical association of heavy metals. Moreover, BMP75 exhibited a higher capacity to adsorb Cu and reduce Cr (VI), which may be related to the functional groups in its biofilm. Overall, this study showed that after biofilms colonization, BMPs of smaller size have more significant potential as a metal vector, and the particle size deserves more scientific attention during the risk assessment.

Hydrodynamic zones and the influence of microorganisms on nitrogen transformation in the diverging area of branched rivers

Diverging area is widespread in river networks, and understanding its biogeochemical process characteristics is of great significance to river ecological restoration and environmental quality improvement. Microbial communities affected by hydrodynamics play an important role in biogeochemical processes, but their relationship in diverging area is little known. Here, the composition of microbial community and its feedback to hydrodynamics and nitrogen conversion in the diverging area of river networks were first studied by coupling ecological theory, biogeochemical theory, microbial DNA sequencing and mathematical model of water environment. The results showed that there were five hydrodynamic zones with significant velocity differences in the diverging area, namely low velocity zone, maximum velocity zone, stagnant zone, separation zone, and deflection zone. According to the flow velocity grouping, there were significant differences in the microbial diversity and abundance among low velocity group, maximum velocity group and stagnant group had significant differences (p < 0.05, stress = 0.1207). In the low velocity group, Firmicutes was the dominant phylum which had a highest abundance and may promot the conversion of organic nitrogen into ammonia nitrogen. In the maximum velocity group, Bdellovibrionota was the dominant phylum which had a highest abundance and may promot the conversion of nitrate and nitric oxide to nitrogen. In the stagnant zone, Methylomirabilota was the dominant phylum which had a highest abundance and may promot the conversion of nitrogen into nitrate and ammonium. In addition, dissolved oxygen was the most sensitive environmental factor for shaping microorganisms and nitrogen conversion in the diverging area of the river networks by canonical correlation analysis. The denitrifying bacteria Rhodocyclaceae, was shown to negatively correlated with the flow velocity. This research improves the scientific basis for the study of the ecosystem in river networks, which will guide the construction of river ecological projects.

Soil plastisphere: Exploration methods, influencing factors, and ecological insights

Microplastic (MP), an emerging contaminant, is globally prevalent and poses potential environmental threats and ecological risks to both aquatic and terrestrial ecosystems. When MPs enter into natural environments, they may serve as artificial substrates for microbial colonization and plastisphere formation, providing new ecological niches for microorganisms. Recent studies of the plastisphere have focused on aquatic ecosystems. However, our understanding of the soil plastisphere e.g. its formation process, microbial ecology, co-transport of organic pollutants and heavy metals, and effects on biogeochemical processes is still very limited. This review summarizes latest methods used to explore the soil plastisphere, assesses the factors influencing the microbial ecology of the soil plastisphere, and sheds light on potential ecological risks caused by the soil plastisphere. The formation and succession of soil plastisphere communities can be driven by MP characteristics and soil environmental factors. The soil plastisphere may affect a series of ecological processes, especially the co-transport of environmental contaminants, biodegradation of MPs, and soil carbon cycling. We aim to narrow the knowledge gap between the soil and aquatic plastisphere, and provide valuable guidance for future research on the soil plastisphere in MP-contaminated soils.

Effects of long-term exposure to silver nanoparticles on the structure and function of microplastic biofilms in eutrophic water

Microplastics are frequently detected in natural aquatic systems proximate to populated areas, such as urban rivers and lakes, and can be rapidly colonized by microbial communities. Microplastics and silver nanoparticles (AgNPs) share similar pathways into natural waters and tend to form heteroaggregations. However, very little is known about the long-term impacts on the structure and function of microplastic biofilms when chronically exposed to silver nanoparticles. Thus, the present study assessed the accumulation property of AgNPs on polymethyl methacrylate (PMMA) microplastics via adsorption tests and studied the chronic effects of AgNPs on the structure and function of microplastic biofilms via 30-day microcosmic experiments in eutrophic water. The adsorption tests showed that the biofilms-colonized PMMA microplastics presented the highest adsorption of 0.98 mg/g in the 1 mg/L AgNPs microcosms. After the 30-day exposure, lactic dehydrogenase release and reactive oxygen species generation of PMMA biofilms increased by 33.23% and 23.98% compared to the MPs-control group with no-AgNPs, indicating that the number of dead cells colonizing microplastics significantly increased. Network analysis suggested that the stabilization of the bacterial community declined with the long-term exposure to AgNPs through the reduction of the modularity and average path length of the network. Compared to the MPs-control group, long-term exposure to AgNPs caused cumulatively inhibitory effects on the nitrogen removal and the N₂O emissions in eutrophic water. The isotopomer analysis revealed that the contribution rate of NO₂^- reduction to N₂O emissions was gradually increasing with the AgNPs exposure. Real-time PCR analysis showed that denitrification genes were less sensitive to AgNPs than the nitrification genes, with gene nosZ performed the most negligible response. Overall, our results revealed that long-term exposure to AgNPs could alter biogeochemical cycling involved by microplastic biofilms and cumulatively reduce the self-recovery of the eutrophic ecosystem.

Indole metabolism by phenol-stimulated activated sludges: Performance, microbial communities and network analysis

Indole and phenol often coexist in the coking wastewater, while the effects of phenol on microbial communities of indole metabolism were less explored. In this study, the microbial interactions within activated sludge microbial communities stimulated by indole (group A) or by indole and phenol (group B) were systematically investigated in sequencing batch reactors (SBRs). The results showed that the removal of indole was increased by adding phenol. By using high-throughput sequencing technology, it was found that α-diversity was reduced in both groups. According to the relative abundance analysis, the indole-degrading genus Comamonas was the core genus in both groups (33.94% and 61.40%). But another indole-degrading genus Pseudomonas was only enriched in group A with 12.22% relative abundance. Meanwhile, common aromatic degrading genus Dyella and Thermomonas were enriched only in group B. It was found that the relative abundance of cytochrome P450 and styrene degradation enzymes were increased in group B by PICRUSt analysis. Based on the phylogenetic molecular ecological networks (pMENs), module hub OTU_1149 (Burkholderia) was only detected in group B, and the positive interactions between the key functional genus Burkholderia and other bacteria were increased. This study provides new insights into our understanding of indole metabolism communities stimulated by phenol, which would provide useful information for practical coking wastewater treatment.

High-Resolution Screening for Marine Prokaryotes and Eukaryotes With Selective Preference for Polyethylene and Polyethylene Terephthalate Surfaces

Marine plastic debris serve as substrates for the colonization of a variety of prokaryote and eukaryote organisms. Of particular interest are the microorganisms that have adapted to thrive on plastic as they may contain genes, enzymes or pathways involved in the adhesion or metabolism of plastics. We implemented DNA metabarcoding with nanopore MinION sequencing to compare the 1-month-old biomes of hydrolyzable (polyethylene terephthalate) and non-hydrolyzable (polyethylene) plastics surfaces vs. those of glass and the surrounding water in a Mediterranean Sea marina. We sequenced longer 16S rRNA, 18S rRNA, and ITS barcode loci for a more comprehensive taxonomic profiling of the bacterial, protist, and fungal communities, respectively. Long read sequencing enabled high-resolution mapping to genera and species. Using previously established methods we performed differential abundance screening and identified 30 bacteria and five eukaryotic species, that were differentially abundant on plastic compared to glass. This approach will allow future studies to characterize the plastisphere communities and to screen for microorganisms with a plastic-metabolism potential.

Long-term effect of fulvic acid amendment on the anammox biofilm system at 15 ℃: performance, microbial community and metagenomics analysis

The role of fulvic acid (FA) on the anammox system at 15 ℃ was investigated. After operation for 113 days, total inorganic nitrogen removal efficiency in FA amendment reactor achieved to 58.6% on average, higher than that of control group (42.1%). Anammox-related functional genes, i.e., hzo and hzs, also demonstrated higher expression level after introduction of FA. It was observed that Candidatus Kuenenia became more competitive than Candidatus Brocadia with the existence of FA at 15 ℃. Also, co-occurrence analysis showed that FA stimulated the complexity and interactive relationship of microbial communities in the anammox system. Metagenomics analysis revealed that FA introduction stimulated relative abundances of genes in central pathway of tricarboxylic acid cycle such as ACO, IDH, OGDH, SCS, FUM, and MDH. Meanwhile, metabolomics analysis revealed that metabolites related to amino sugar metabolic pathways (glucose 1-phosphate, UDP-D-glucuronate, UDP) and redox reactions (NAD⁺ and NADH) improved in the FA amendment reactor.

Contribution of stochastic processes to the microbial community assembly on field-collected microplastics

A growing body of evidence suggests that microplastics may be colonized with a unique microbiome, termed 'plastisphere', in aquatic environments. However, the deep mechanisms (deterministic and/or stochastic processes) underlying the community assembly on microplastics are still poorly understood. Here, we took the estuary of Hangzhou Bay (Zhejiang, China) as an example and examined the assembly mechanisms of bacterial communities in water and microplastic samples. Results from high-throughput sequencing showed that Proteobacteria, Firmicutes, and Actinobacteria were the dominant phyla across all samples. Additionally, microorganisms from plastisphere and planktonic communities exhibited contrasting taxonomic compositions, with greater within-group variation for microplastic samples. The null model analysis indicated the plastisphere bacterial communities were dominantly driven by the stochastic process of drift (58.34%) and dispersal limitation (23.41%). The normalized stochasticity ratio (NST) also showed that the community assembly on microplastics was more stochastic (NST > 50%). Based on the Sloan neutral community model, the migration rate for plastisphere communities (0.015) was significantly lower than that for planktonic communities (0.936), potentially suggesting that it is the stochastic balance between loss and gain of bacteria (e.g., stochastic births and deaths) critically shaping the community assembly on microplastics and generating the specific niches. This study greatly enhanced our understanding of the ecological patterns of microplastic-associated microbial communities in aquatic environments.

Periphytic Biofilm Formation on Natural and Artificial Substrates: Comparison of Microbial Compositions, Interactions, and Functions

Periphytic biofilms have been widely used in wastewater purification and water ecological restoration, and artificial substrates have been progressively used for periphyton immobilisation to substitute natural substrates. However, there is insufficient knowledge regarding the interaction network structure and microbial functions in biofilm communities on artificial substrates, which are essential attribute affecting their applications in biofilm immobilisation. This study compared the community structure, co-occurrence network, and metabolic functions of bacterial and microeukaryotic periphytic biofilms during a 35-day indoor cultivation on artificial substrates, such as artificial carbon fibre (ACF) and polyvinyl chloride (PVC), and natural substrates, such as pebble and wood. Results demonstrated that different types of artificial substrates could affect the community composition and functional diversity of bacterial and microeukaryotic biofilms. The bacterial and microeukaryotic community on ACF and PVC showed significantly higher Simpson index compared to those on wood. Bacterial networks on artificial substrates were more complex than those on natural substrates, while the keystone species on natural substrates were more abundant, indicating that the bacterial communities on artificial substrates had stronger stability and resistance to external interference. Furthermore, the functional metabolic profiles predicted showed the abilities of bacterial communities to metabolise nitrogen and carbon sources colonised on artificial substrates were stronger than those on natural substrates. These findings demonstrated that artificial substrates could be special niches for microbial colonisation, possibly altering microbial compositions, interactions, and functions. Therefore, this study provides a powerful theoretical basis for choosing suitable artificial substrates for microbial aggregation and immobilisation technology.