Distinct mechanisms underlying the assembly of microeukaryotic generalists and specialists in an anthropogenically impacted river

Biogeographic patterns of meio- and micro-eukaryotic communities in dam-induced river-reservoir systems

Although the Three Gorges Dam (TGD) is the world's largest hydroelectric dam, little is known about the spatial-temporal patterns and community assembly mechanisms of meio- and micro-eukaryotes and its two subtaxa (zooplankton and zoobenthos). This knowledge gap is particularly evident across various habitats and during different water-level periods, primarily arising from the annual regular dam regulation. To address this inquiry, we employed mitochondrial cytochrome c oxidase I (COI) gene-based environmental DNA (eDNA) metabarcoding technology to systematically analyze the biogeographic pattern of the three communities within the Three Gorges Reservoir (TGR). Our findings reveal distinct spatiotemporal characteristics and complementary patterns in the distribution of meio- and micro-eukaryotes. The three communities showed similar biogeographic patterns and assembly processes. Notably, the diversity of these three taxa gradually decreased along the river. Their communities were less shaped by stochastic processes, which gradually decreased along the longitudinal riverine-transition-lacustrine gradient. Hence, deterministic factors, such as seasonality, environmental, and spatial variables, along with species interactions, likely play a pivotal role in shaping these communities. Environmental factors primarily drive seasonal variations in these communities, while hydrological conditions, represented as spatial distance, predominantly influence spatial variations. These three communities followed the distance-decay pattern. In winter, compared to summer, both the decay and species interrelationships are more pronounced. Taken together, this study offers fresh insights into the composition and diversity patterns of meio- and micro-eukaryotes at the spatial-temporal level. It also uncovers the mechanisms behind community assembly in various environmental niches within the dam-induced river-reservoir systems. KEY POINTS: • Distribution and diversity of meio- and micro-eukaryotes exhibit distinct spatiotemporal patterns in the TGR. • Contribution of stochastic processes in community assembly gradually decreases along the river. • Deterministic factors and species interactions shape meio- and micro-eukaryotic community.

Ecological and evolutionary processes involved in shaping microbial habitat generalists and specialists in urban park ecosystems

Microbiomes are integral to ecological health and human well-being; however, their ecological and evolutionary drivers have not been systematically investigated, especially in urban park ecosystems. As microbes have different levels of tolerance to environmental changes and habitat preferences, they can be categorized into habitat generalists and specialists. Here, we explored the ecological and evolutionary characteristics of both prokaryotic and microeukaryotic habitat generalists and specialists from six urban parks across five habitat types, including moss, soil, tree hole, water, and sediment. Our results revealed that different ecological and evolutionary processes maintained and regulated microbial diversity in urban park ecosystems. Under ecological perspective, community assembly of microbial communities was mainly driven by stochastic processes; however, deterministic processes were higher for habitat specialists than generalists. Microbial interactions were highly dynamic among habitats, and habitat specialists played key roles as module hubs in intradomain networks. In aquatic interdomain networks, microeukaryotic habitat specialists and prokaryotic habitat specialists played crucial roles as module hubs and connectors, respectively. Furthermore, analyzing evolutionary characteristics, our results revealed that habitat specialists had a much higher diversification potential than generalists, while generalists showed shorter phylogenetic branch lengths as well as larger genomes than specialists. This study broadens our understanding of the ecological and evolutionary features of microbial habitat generalists and specialists in urban park ecosystems across multi-habitat.

IMPORTANCE

Urban parks, as an important urban greenspace, play essential roles in ecosystem services and are important hotspots for microbes. Microbial diversity is driven by different ecological and evolutionary processes, while little is currently known about the distinct roles of ecological and evolutionary features in shaping microbial diversity in urban park ecosystems. We explored the ecological and evolutionary characteristics of prokaryotic and microeukaryotic habitat generalists and specialists in urban park ecosystems based on a representative set of different habitats. We found that different ecological and evolutionary drivers jointly maintained and regulated microbial diversity in urban park microbiomes through analyzing the community assembly process, ecological roles in hierarchical interaction, and species diversification potential. These findings significantly advance our understanding regarding the mechanisms governing microbial diversity in urban park ecosystems.

Distinct strategies of the habitat generalists and specialists in the Arctic sediments: Assembly processes, co-occurrence patterns, and environmental implications

Microorganisms could be classified as habitat generalists and specialists according to their niche breadth, uncovering their survival strategy is a crucial topic in ecology. Here, differences in environmental adaptation, community assemblies, co-occurrence patterns, and ecological functions between generalists and specialists were explored in the Arctic marine sediments. Compared to specialists, generalists showed lower alpha diversity but stronger environmental adaption, and dispersal limitation contributed more to the community assembly of specialists (74 %) than generalists (46 %). Furthermore, the neutral theory model demonstrated that generalists (m = 0.20) had a higher immigration rate than specialists (m = 0.02), but specialists exhibited more complex co-occurrence patterns than generalists. Our results also found that generalists may play more important roles in C, N, S metabolism but are weaker in carbon fixation and xenobiotic biodegradation and metabolism. This study would broaden our understanding of bacterial generalists' and specialists' survival strategies, and further reveal their ecological functions in marine sediments.

Seasonality regulates the distinct assembly patterns of microeukaryotic plankton communities in the Three Gorges Reservoir, China

The hydrographic and environmental factors along the Three Gorges Reservoir (TGR) have been significantly altered since the Three Gorges Dam (TGD) began working in 2006. Here, we collected 54 water samples, and then measured the environmental factors, followed by sequencing of the 18S rRNA gene and subsequent analysis of community assembly mechanisms. The findings indicated that the majority of environmental variables (such as AN, TP, Chl-a, CODMn, and Cu) exhibited both temporal and spatial variations due to the influences of the TGD. The distribution of different environmental factors and microeukaryotic plankton communities is influenced by the changing seasons. The community structure in TGR showed variations across three seasons, possibly due to variations in their environmental preferences, inherent dissimilarities, and seasonal succession. Furthermore, different communities exhibited a comparable distance-decay trend, suggesting that distinct taxa are likely to exhibit a similar spatial distribution. In addition, the community formation in TGR was influenced by both deterministic and stochastic factors, with the balance between them being mainly controlled by the season. Specifically, deterministic processes could explain 33.9-51.1% of community variations, while stochastic processes could contribute 23.5-32.2%. The findings of this research demonstrated that the varying ecological processes' significance relied on environmental gradients, geographical scale, and ecological conditions. This could offer a fresh outlook on comprehending the composition, assembly mechanisms, and distribution patterns of microeukaryotic plankton in reservoir ecosystems.

Deciphering soil resistance and virulence gene risks in conventional and organic farming systems

Organic farming is a sustainable agricultural practice emphasizing natural inputs and ecological balance, and has garnered significant attention for its potential health and environmental benefits. However, a comprehensive evaluation of the emergent contaminants, particularly resistance and virulence genes within organic farming system, remains elusive. Here, a total of 36 soil samples from paired conventional and organic vegetable farms were collected from Jiangsu province, China. A systematic metagenomic approach was employed to investigate the prevalence, dispersal capability, pathogenic potential, and drivers of resistance and virulence genes across both organic and conventional systems. Our findings revealed a higher abundance of antibiotic resistance genes (ARGs), biocide resistance genes (BRGs), and virulence factor genes (VFGs) in organic farming system, with ARGs exhibiting a particularly notable increase of 10.76% compared to the conventional one. Pathogens such as Pseudomonas aeruginosa, Escherichia coli, and Mycobacterium tuberculosis were hosts carrying all four gene categories, highlighting their potential health implications. The neutral community model captured 77.1% and 71.9% of the variance in community dynamics within the conventional and organic farming systems, respectively, indicating that stochastic process was the predominant factor shaping gene communities. The relative smaller m value calculated in organic farming system (0.021 vs 0.023) indicated diminished gene exchange with external sources. Moreover, farming practices were observed to influence the resistance and virulence gene landscape by modifying soil properties, managing heavy metal stress, and steering mobile genetic elements (MGEs) dynamics. The study offers insights that can guide agricultural strategies to address potential health and ecological concerns.

Spatiotemporal assembly and functional composition of planktonic microeukaryotic communities along productivity gradients in a subtropical lake

Microeukaryotes play crucial roles in the microbial loop of freshwater ecosystems, functioning both as primary producers and bacterivorous consumers. However, understanding the assembly of microeukaryotic communities and their functional composition in freshwater lake ecosystems across diverse environmental gradients remains limited. Here, we utilized amplicon sequencing of 18S rRNA gene and multivariate statistical analyses to examine the spatiotemporal and biogeographical patterns of microeukaryotes in water columns (at depths of 0.5, 5, and 10 m) within a subtropical lake in eastern China, covering a 40 km distance during spring and autumn of 2022. Our results revealed that complex and diverse microeukaryotic communities were dominated by Chlorophyta (mainly Chlorophyceae), Fungi, Alveolata, Stramenopiles, and Cryptophyta lineages. Species richness was higher in autumn than in spring, forming significant hump-shaped relationships with chlorophyll a concentration (Chl-a, an indicator of phytoplankton biomass). Microeukaryotic communities exhibited significant seasonality and distance-decay patterns. By contrast, the effect of vertical depth was negligible. Stochastic processes mainly influenced the assembly of microeukaryotic communities, explaining 63, 67, and 55% of community variation for spring, autumn, and both seasons combined, respectively. Trait-based functional analysis revealed the prevalence of heterotrophic and phototrophic microeukaryotic plankton with a trade-off along N:P ratio, Chl-a, and dissolved oxygen (DO) gradients. Similarly, the mixotrophic proportions were significantly and positively correlated with Chl-a and DO concentrations. Overall, our findings may provide useful insights into the assembly patterns of microeukaryotes in lake ecosystem and how their functions respond to environmental changes.

Development, validation, and application of a microbial community-based index of biotic integrity for assessing the ecological status of a peri-urban watershed in China

This study represents the pioneering effort in employing 16S rRNA-bacteria and 18S rRNA-microeukaryotes to construct the microbial community-based index of biotic integrity (MC-IBI) for assessing the ecological health of riverine ecosystems. The MC-IBI was developed, validated, and implemented using water samples from the Changle River watershed, encompassing both wet and dry seasons. A total of 205 metrics, containing microbial diversity, composition, pollution tolerance/sensitivity, and functional categories, were selected as candidates for evaluation. Following a rigorous screening process, five core metrics were identified as key indicators, namely Pielou's evenness of microeukaryotes, %Cryptophyceae, %Proteobacteria, %Oxyphotobacteria, and % 16S rRNA gene-human pathogens. Moreover, redundancy analysis revealed three metrics (i.e., Pielou's evenness, % 16S rRNA gene-human pathogens, and % Proteobacteria) were positively correlated with impairment conditions. In contrast, two metrics (i.e., %Oxyphotobacteria and %Cryptophyceae) were associated positively with reference conditions. Notably, the developed MC-IBI demonstrates clear discrimination between reference and impaired sites and significantly correlates with environmental parameters and land use patterns. A path model analysis revealed that land use patterns (i.e., build-up land, cropland) negatively impacted the MC-IBI scores. The application of the MC-IBI method yielded an assessment of the ecological conditions at the 73 sampling locations within the Changle River watershed, assigning them into categories of "Very good" (4.1 %), "Good" (4.1 %), "Moderate" (5.5 %), "Poor" (21.9 %), and "Very poor" (64.4 %). This bioassessment framework presents an innovative approach toward the preservation, maintenance, and management of riverine ecosystems.

Biogeographic patterns of micro-eukaryotic generalists and specialists and their effects on regional α-diversity at inter-oceanic scale

Inter-oceanic scale studies allow us to understand the global spread of micro-organisms in marine ecosystems. In this study, micro-eukaryotic communities in marine surface sediment were collected from tropical to Arctic sites. We found that micro-eukaryotic generalists had much higher intraspecific variation than specialists which allow them to distribute more widely through higher spatiotemporal asynchrony and complementary niche preferences among conspecific taxa. Moreover, comparing to the host-associated protozoa and small metazoa, the algae and free-living protozoa with higher intraspecific variation allow them to have wider distribution ranges. Species abundance also played an important role in driving the distribution ranges of generalists and specialists. The generalists had important effects on regional α-diversity even at an inter-oceanic scale which led to the micro-eukaryotic species richness in polar sites to be mainly influenced by the regional generalists but not the local specialists. In particular, more than 97% of algal species in polar sites were shared with the tropical and subtropical sites (including toxic dinoflagellate). Overall, our study suggests that the effects of global change and human activities on the vulnerable high latitude habitats may lead to biotic homogenization for the whole microbial community (not only the dispersal of some harmful algae) through the potential long-distance spread of generalists.

Bacterial and Microeukaryotic Community Compositions and Their Assembly Processes in Lakes on the Eastern Qinghai-Tibet Plateau

Bacterial and microeukaryotic community compositions and their assembly processes have remained challenging and remained unclear in lake ecosystems on the Qinghai-Tibet Plateau (QTP). We revealed the diversity and community compositions, driving factors, ecological assembly processes, and co-occurrence networks of bacterial and microeukaryotic communities in water bodies of the eight lake ecosystems across the Eastern QTP. The results demonstrated that the predominant bacteria in most samples were Proteobacteria, with an average relative abundance of 41.78%, whereas the most abundant of microeukaryotes differed among the sample sites. The redundancy analysis revealed that latitude and pH were the most important driving factors in shaping the bacterial and microeukaryotic community compositions. Homogeneous selection (56.40%) was the dominant process in assembling the bacterial communities, whereas dispersal limitation (67.24%) was the major process in governing the microeukaryotic communities. Furthermore, dissolved organic carbon and salinity were the major factors mediating the balance of deterministic and stochastic assembly processes in the bacterial and microeukaryotic communities. Both the bacterial and microeukaryotic community co-occurrence networks exhibited topological features of modularity and non-random topological features. The results offer insights into the mechanisms underpinning bacterial and microeukaryotic diversities and communities in the lake ecosystems on the QTP.

Distinct spatiotemporal succession of bacterial generalists and specialists in the lacustrine plastisphere

The assembly processes of generalists and specialists and their driving mechanisms during spatiotemporal succession is a central issue in microbial ecology but a poorly researched subject in the plastisphere. We investigated the composition variation, spatiotemporal succession, and assembly processes of bacterial generalists and specialists in the plastisphere, including non-biodegradable (NBMPs) and biodegradable microplastics (BMPs). Although the composition of generalists and specialists on NBMPs differed from that of BMPs, colonization time mainly mediated the composition variation. The relative abundance of generalists and the relative contribution of species replacement were initially increased and then decreased with colonization time, while the specialists initially decreased and then increased. Besides, the richness differences also affected the composition variation of generalists and specialists in the plastisphere, and the generalists were more susceptible to richness differences than corresponding specialists. Furthermore, the assembly of generalists in the plastisphere was dominated by deterministic processes, while stochastic processes dominated the assembly of specialists. The network stability test showed that the community stability of generalists on NBMPs and BMPs was lower than corresponding specialists. Our results suggested that different ecological assembly processes shaped the spatiotemporal succession of bacterial generalists and specialists in the plastisphere, but were less influenced by polymer types.

Cd contamination determined assembly processes and network stability of AM fungal communities in an urban green space ecosystem

The effects of cadmium (Cd) contamination on the assembly mechanism and co-occurrence patterns of arbuscular mycorrhizal (AM) fungal communities remain unclear, especially in urban green spaces. This study sequenced AM fungal communities in greenbelt soils in Zhengzhou (China). The effects of Cd contamination on the AM fungal diversity, community assembly processes, and co-occurrence patterns were explored. We found that (1) an increase in Cd contamination changed the community composition, which resulted in a significant improvement in the diversity of specialists of AM fungi and a significant decrease in the diversity of generalists. (2) Deterministic processes dominated the community assembly of specialists and stochastic processes dominated the community assembly of generalists. (3) Specialists played a more important role than generalists in maintaining the stability of AM fungal networks under Cd contamination. Overall, Cd contamination affected the ecological processes of AM fungi in urban green space ecosystems. However, the effects on the assembly processes and network stability of different AM fungi taxa (specialists and generalists) differed significantly. The present study provides deeper insight into the effect of Cd contamination on the ecological processes of AMF and is helpful in further exploring the ecological risk of Cd contamination in urban green spaces.

The Variations of Microbial Diversity and Community Structure Along Different Stream Orders in Wuyi Mountains

The surface water is an important habitat for freshwater microorganisms, but there is a lack of understanding of the pattern of microbial diversity and structure in stream continuums of small subtropical forest watersheds. Therefore, this study aimed to understand the variations in microbial diversity and community structure along stream orders (1-5) in the small subtropical forest catchments of the Wuyi Mountains. Using GIS software, 20 streams were chosen and classified into 5 orders. Illumina sequencing was used to analyze the dynamics of microbial communities, along with stream orders and hydro-chemical properties of stream water were also determined. Our results indicated that the bacterial and fungal richness (ACE index) was higher in low-order (1 and 2 orders) streams than in high-order (3, 4, and 5 orders) streams, with the highest value in the order 2 streams (P < 0.05). The water temperature and dissolved oxygen were positively correlated with fungal richness (P < 0.05). The bacterial rare taxa had a significant correlation with the abundance taxa (P < 0.05). The relative abundances of Bacteroidetes, Actinobacteria, and Chytridiomycota microbial phyla were significantly different among different order streams (P < 0.05). Using the neutral community model, we found that the fungal community structure was significantly shaped by hydro-chemical properties, while the bacterial community structure was largely regulated by stochastic processes. Our findings suggest that variations in microbial community structure in subtropical headwaters are largely shaped by the water temperature and dissolved oxygen.

Unraveling bacterial and eukaryotic communities in secondary water supply systems: Dynamics, assembly, and health implications

Secondary water supply systems (SWSSs) are crucial water supply infrastructures for high-rise buildings in metropolitan cities. In recent years, they have garnered public attention due to increased microbial risks. However, our understanding of SWSS microbial ecology, particularly concerning the composition of eukaryotes and the underlying mechanisms driving microbial dynamics and assembly in SWSSs, remains elusive. Herein, we conducted a comprehensive investigation on both eukaryotes and bacteria along the water transportation pathway and across various microbial habitats (water, biofilm, and sediment) in SWSSs. Sequencing results revealed that eukaryotes within SWSSs predominantly consist of protists (average abundance: 31.23%) and metazoans (20.91%), while amoebae accounted for 4.71% of the total. During water transportation from the distribution mains to taps, both bacterial and eukaryotic communities exhibited significant community shifts, and higher degrees of variation were observed for eukaryotic community among different locations within SWSSs. The normalized stochasticity ratio (NST) analysis demonstrated that bacterial community assembly was governed by stochastic processes, while eukaryotic community assembly was primarily shaped by deterministic processes. Within SWSS tanks, bacterial communities significantly varied across water, biofilm, and sediment, whereas eukaryotic communities showed minor differences among these habitats. The co-occurrence networks analysis revealed that tank biofilm and sediment harbored more eukaryote-bacterium linkages than water, suggesting biofilm and sediment might be hotspots for inter-kingdom interactions. We also applied FEAST analysis to track the source of tap water microbiota, results of which showed that household-tap bacteria mainly originated from tank water. In contrast, tank biofilm was identified as the primary microbial source to eukaryotes in household tap water. Additionally, engineering factors such as tank materials significantly affected amoeba community, and the SWSS configuration was found to influence Legionella and Mycobacterium abundances in SWSSs. Overall, results of our study shed light on the microbial ecology in SWSS and provide insights into SWSS management and health risk control.

PacBio next-generation sequencing uncovers Apicomplexa diversity in different habitats

The phylum Apicomplexa comprises a large group of intracellular protozoan parasites. These microorganisms are known to infect a variety of vertebrate and invertebrate hosts, leading to significant medical and veterinary conditions such as toxoplasmosis, cryptosporidiosis, theileriosis, and eimeriosis. Despite their importance, comprehensive data on their diversity and distribution, especially in riverine environments, remain scant. To bridge this knowledge gap, we utilized next-generation high-throughput 18S rRNA amplicon sequencing powered by PacBio technology to explore the diversity and composition of the Apicomplexa taxa. Principal component analysis (PCA) and principal coordinate analysis (PCoA) indicated the habitat heterogeneity for the physicochemical parameters and the Apicomplexa community. These results were supported by PERMANOVA (P < 0.001), ANOSIM (P < 0.001), Cluster analysis, and Venn diagram. Dominant genera of Apicomplexa in inlet samples included Gregarina (38.54%), Cryptosporidium (32.29%), and Leidyana (11.90%). In contrast, outlet samples were dominated by Babesia, Cryptosporidium, and Theileria. While surface water samples revealed 16% and 8.33% relative abundance of Toxoplasma and Cryptosporidium, respectively. To our knowledge, the next-generation high throughput sequencing covered a wide range of parasites in Egypt for the first time, which could be useful for legislation of the standards for drinking water and wastewater reuse.

Actinobacteria produce taste and odor in drinking water reservoir: Community composition dynamics, co-occurrence and inactivation models

Taste and odor (T&O) has become a significant concern for drinking water safety. Actinobacteria are believed to produce T&O during the non-algal bloom period; however, this has not been widely investigated. In this study, the seasonal dynamics of the actinobacterial community structure and inactivation of odor-producing actinobacteria were explored. The results indicated that the diversity and community composition of actinobacteria exhibited significant spatiotemporal distribution. Network analysis and structural equation modeling showed that the actinobacterial community occupied a similar environmental niche, and the major environmental attributes exhibited spatiotemporal dynamics, which affected the actinobacterial community. Furthermore, the two genera of odorous actinobacteria were inactivated in drinking water sources using chlorine. Amycolatopsis spp. have a stronger chlorine resistance ability than Streptomyces spp., indicating that chlorine inactivates actinobacteria by first destroying cell membranes and causing the release of intracellular compounds. Finally, we integrated the observed variability in the inactivation rate of actinobacteria into an expanded Chick-Watson model to estimate its effect on inactivation. These findings will deepen our understanding of the seasonal dynamics of actinobacterial community structure in drinking water reservoirs and provide a foundation for reservoir water quality management strategies.

Synergistic analysis of performance, functional genes, and microbial community assembly in SNDPR process under Zn(II) stress

One of the most prevalent heavy metals found in rural sewage is Zn(II), while its effect on simultaneous nitrification, denitrification and phosphorus removal (SNDPR) remains unclear. In this work, the responses of SNDPR performance to long-term Zn(II) stress were investigated in a cross-flow honeycomb bionic carrier biofilm system. The results indicated that Zn(II) stress at 1 and 5 mg L^-1 could increase nitrogen removal. Maximum ammonia nitrogen, total nitrogen, and phosphorus removal efficiencies of up to 88.54%, 83.19%, and 83.65% were obtained at Zn(II) concentration of 5 mg L^-1. The functional genes, such as archaeal amoA, bacterial amoA, NarG, NirS, NapA, and NirK, also reached the highest value at 5 mg L^-1 Zn(II), with the absolute abundances of 7.73 × 10⁵, 1.57 × 10⁶, 6.68 × 10⁸, 1.05 × 10⁹, 1.79 × 10⁸, and 2.09 × 10⁸ copies·g^-1 dry weight, respectively. The neutral community model demonstrated that deterministic selection was responsible for the system's microbial community assembly. Additionally, response regimes with extracellular polymeric substances and cooperation among microorganisms facilitated the stability of the reactor effluent. Overall, the findings of this paper contribute to improving the efficiency of wastewater treatment.

Wastewater treatment plant effluent discharge decreases bacterial community diversity and network complexity in urbanized coastal sediment

The wastewater treatment plant (WWTP) effluent discharge affects the microorganisms in the receiving water bodies. Despite the ecological significance of microbial communities in pollutant degradation and element cycling, how the community diversity is affected by effluent remains obscure. Here, we compared the sediment bacterial communities exposed to different intensities of WWTP effluent discharge in Hangzhou Bay, China: i) a severely polluted area that receives effluent from an industrial WWTP, ii) a moderately polluted area that receives effluent from a municipal WWTP, and iii) less affected area that inner the bay. We found that the sediment bacterial diversity decreased dramatically with pollution levels of inorganic nutrients, heavy metals, and organic halogens. Microbial community assembly model analysis revealed increased environmental selection and decreased species migration rate in the severely polluted area, resulting in high phylogenetic clustering of the bacterial communities. The ecological networks were less complex in the two WWTP effluent receiving areas than in the inner bay area, as suggested by the smaller network size and lower modularity. Fewer negative network associations were detected in the severely (6.7%) and moderately (8.3%) polluted areas than in the less affected area (16.7%), indicating more collaborative inter-species behaviors are required under stressful environmental conditions. Overall, our results reveal the fundamental impacts of WWTP effluents on the ecological processes shaping coastal microbial communities and point to the potential adverse effects of diversity loss on ecosystem functions.

Exposure to benzalkonium chloride disinfectants promotes antibiotic resistance in sewage sludge microbiomes

Disinfectants are routinely used in human environments to control and prevent the transmission of microbial disease, and this is particularly true during the current COVID-19 crisis. However, it remains unclear whether the increased disinfectant loadings to wastewater treatment plants facilitate the dissemination of antibiotic resistance genes (ARGs) in sewage sludge microbiomes. Here, we investigated the impacts of benzalkonium chlorides (BACs), widely used disinfectants, on ARGs profiles and microbial community structures in sewage sludge by using high-throughput quantitative PCR and Illumina sequencing. A total of 147 unique ARGs and 39 mobile genetic elements (MGEs) were detected in all sewage sludge samples. Our results show that exposure to BACs disinfectants at environmentally relevant concentrations significantly promotes both the diversity and absolute abundance of ARGs in sludge microbiomes, indicating the co-selection of ARGs by BACs disinfectants. The enrichment of ARGs abundance varied from 2.15-fold to 3.63-fold compared to controls. In addition, BACs exposure significantly alters bacterial and protistan communities, resulting in dysbiosis of the sludge microbiota. The Mantel test and Procrustes analysis confirm that bacterial communities are significantly correlated with ARGs profiles under BACs treatments. The structural equation model explains 83.8 % of the total ARGs variation and further illustrates that the absolute abundance of MGEs exerts greater impacts on the variation of absolute abundance of ARGs than microbial communities under BACs exposure, suggesting BACs may promote antibiotic resistance by enhancing the horizontal gene transfer of ARGs across sludge microbiomes. Collectively, our results provide new insights into the proliferation of antibiotic resistance through disinfectant usage during the pandemic and highlight the necessity to minimize the environmental release of disinfectants into the non-target environment for combating antibiotic resistance.

Satellite taxa regulated the response of constructed wetlands microeukaryotic community to changing hydraulic loading rate

Revealing how species interaction and assembly processes structure the core and satellite microeukaryotic subcommunities in an engineering environment is crucial for understanding how biodiversity influences system function. By investigating the core and satellite microeukaryotic subcommunities in constructed wetlands (CWs), we depicted an integrated distribution pattern of microeukaryotic communities in the CWs with different hydraulic loading rates (HLRs). Surprisingly, our results suggested that high HLR reduced the diversity and network stability of the microeukaryote community in CW. The stochastic process becomes more important with the increased HLR. In addition, satellite and core taxa varied inconsistently under different HLRs except for niche breadth. And the changes in all taxa were consistent with those in satellite taxa. Satellite taxa, but not core taxa, was an important driver in shaping the dynamics of microeukaryotic communities and played an important role in maintaining the stability of the microeukaryotic community. Overall, our results not only fill a gap in understanding the microeukaryotic community dynamics and its basic drivers of CWs under different HLRs but also highlights the particular importance of satellite microeukaryotes in mediating biogeochemical cycles in CWs ecosystems.

Gut microbiota of white-headed black langurs (Trachypithecus leucocephalus) in responses to habitat fragmentation

The white-headed black langur (Trachypithecus leucocephalus) is exclusively distributed in the karst forests and is critically endangered owing to habitat fragmentation. Gut microbiota can provide physiological data for a comprehensive study of the langur's response to human disturbance in the limestone forest; to date, data on spatial variations in the langurs' gut microbiota are limited. In this study, we examined intersite variations in the gut microbiota of white-headed black langurs in the Guangxi Chongzuo White-headed Langur National Nature Reserve, China. Our results showed that langurs in the Bapen area with a better habitat had higher gut microbiota diversity. In the Bapen group, the Bacteroidetes (13.65% ± 9.73% vs. 4.75% ± 4.70%) and its representative family, Prevotellaceae, were significantly enriched. In the Banli group, higher relative abundance of Firmicutes (86.30% ± 8.60% vs. 78.85% ± 10.35%) than the Bapen group was observed. Oscillospiraceae (16.93% ± 5.39% vs. 16.13% ± 3.16%), Christensenellaceae (15.80% ± 4.59% vs. 11.61% ± 3.60%), and norank_o__Clostridia_UCG-014 (17.43% ± 6.64% vs. 9.78% ± 3.83%) were increased in comparison with the Bapen group. These intersite variations in microbiota diversity and composition could be accounted for by differences in food resources caused by fragmentation. Furthermore, compared with the Banli group, the community assembly of gut microbiota in the Bapen group was influenced by more deterministic factors and had a higher migration rate, but the difference between the two groups was not significant. This might be attributed to the serious fragmentation of the habitats for both groups. Our findings highlight the importance of gut microbiota response for the integrity of wildlife habitats and the need in using physiological indicators to study the mechanisms by which wildlife responds to human disturbances or ecological variations.

Response and recovery mechanisms of river microorganisms to gradient concentrations of estrogen

As an important ecological system on the earth, rivers have been influenced by the rapid development of urbanization, industrialization, and anthropogenic activities. Increasingly more emerging contaminants, such as estrogens, are discharged into the river environment. In this study, we conducted river water microcosmic experiments using in situ water to investigate the response mechanisms of microbial community when exposed to different concentrations of target estrogen (estrone, E1). Results showed that both exposure time and concentrations shaped the diversity of microbial community when exposed to E1. Deterministic process played a vital role in influencing microbial community over the entire sampling period. The influence of E1 on microbial community could last for a longer time even after the E1 has been degraded. The microbial community structure could not be restored to the undisturbed state by E1, even if disturbed by low concentrations of E1(1 μg/L and 10 μg/L) for a short time. Our study suggests that estrogens could cause long-term disturbance to the microbial community of river water ecosystem and provides a theoretical basis for assessing the environmental risk of estrogens in rivers.

Temporal Succession of Bacterial Community Structure, Co-occurrence Patterns, and Community Assembly Process in Epiphytic Biofilms of Submerged Plants in a Plateau Lake

In shallow macrophytic lakes, epiphytic biofilms are formed on the surface of submerged plant stems and leaves because of algae and bacterial accumulation. Epiphytic biofilms significantly impact the health of the host vegetation and the biogeochemical cycling of lake elements. However, community diversity, species interactions, and community assembly mechanisms in epiphytic bacterial communities (EBCs) of plants during different growth periods are not well understood. We investigated the successional dynamics, co-occurrence patterns, and community assembly processes of epiphytic biofilm bacterial communities of submerged plants, Najas marina and Potamogeton lucens, from July to November 2020. The results showed a significant seasonal variation in EBC diversity and richness. Community diversity and richness increased from July to November, and the temperature was the most important driving factor for predicting seasonal changes in EBC community structure. Co-occurrence network analysis revealed that the average degree and graph density of the network increased from July to November, indicating that the complexity of the EBC network increased. The bacterial community co-occurrence network was limited by temperature, pH, and transparency. The phylogeny-based null model analysis showed that deterministic processes dominated the microbial community assembly in different periods, increasing their contribution. In addition, we found that as the dominance of deterministic processes increased, the microbial co-occurrence links increased, and the potential interrelationships between species became stronger. Thus, the findings provide insights into the seasonal variability of EBC assemblage and co-occurrence patterns in lacustrine ecosystems.

Denitrifying anaerobic methane-oxidizing bacteria in river networks of the Taihu Basin: Community dynamics and assembly process

Denitrifying anaerobic methane-oxidizing bacteria (DAMO bacteria) plays an important role in reducing methane emissions from river ecosystems. However, the assembly process of their communities underlying different hydrologic seasons remains unclarified. In this study, the dynamics of DAMO bacterial communities in river networks of the Taihu Basin were investigated by amplicon sequencing across wet, normal, and dry seasons followed by multiple statistical analyses. Phylogenetic analysis showed that Group B was the major subgroup of DAMO bacteria and significant dynamics for their communities were observed across different seasons (constrained principal coordinate analysis, p = 0.001). Furthermore, the neutral community model and normalized stochasticity ratio model were applied to reveal the underlying assembly process. Stochastic process and deterministic process dominated the assembly process in wet season and normal season, respectively and similar contributions of deterministic and stochastic processes were observed in dry season. Meanwhile, abundant (relative abundance >0.1%) and rare (relative abundance <0.01%) DAMO bacterial communities were found to be shaped via distinct assembly processes. Deterministic and stochastic processes played a considerable role in shaping abundant DAMO bacterial communities, while deterministic process mainly shaped rare DAMO bacterial communities. Results of this study revealed the dynamics of DAMO bacterial communities in river networks and provided a theoretical basis for further understanding of the assembly process.

Contamination with multiple heavy metals decreases microbial diversity and favors generalists as the keystones in microbial occurrence networks

Soil contamination with multiple heavy metals poses threats to human health and ecosystem functioning. Using the Nemerow pollution index, which considers the effects of multiple heavy metals, we compared the diversity and composition of bacteria, fungi and protists and their potential interactions in response to a multi-metal contamination gradient. Multi-metal contamination significantly altered the community composition of bacteria, fungi and protists, and the degree of alteration increased with increasing severity of contamination. The alpha-diversity of bacteria, fungi and protists significantly decreased with increasing contamination level. The dominant generalists, found in all soil samples, were Gammaproteobacteria, Chloroflexi and Bacillus sp, whereas the dominant specialists were Anaerolineaceae, Entoloma sp. and Sandonidae_X sp. The relative abundances of generalists were positively correlated, whereas those of specialists were negatively correlated, with the Nemerow pollution index. In addition, the complexity of the microbial co-occurrence network increased with increasing contamination level. Generalists, rather than specialists, were the keystones in the microbial co-occurrence network and played a crucial role in adaptation to multi-metal contamination through enhanced potential interactions within the entire microbiome. Our results provide insights into the ecological effects of multi-metal contamination on the soil microbiome and will help to develop bio-remediation technologies for contaminated soils.

Community assembly of microbial habitat generalists and specialists in urban aquatic ecosystems explained more by habitat type than pollution gradient

Urban freshwater ecosystems have important ecosystem functions, provide habitats for diverse microbial communities and are susceptible to multiple interconnected factors such as environmental pollution. Despite the ecological significance of bacteria and microeukaryotes, little is known about how their community assembly responds to various environmental factors across water and sediment habitats and ecological processes shaping them. Here, environmental DNA-based approaches were used to investigate the community assembly processes of bacteria and microeukaryotes (including habitat generalists and specialists) in urban water and sediment across an urban-pollution gradient in Wuhan, central China. The diversity, community composition and potential function of bacteria and microeukaryotes showed significantly stronger variation between water and sediment than across an urban pollution gradient. Although, bacterial and microeukaryotic community assemblies were dominated by strong selection processes in both water and sediment habitats, but a contrasting community assembly mechanism was identified between habitat generalists and specialists. Bacterial and microeukaryotic communities showed a greater response to physicochemical variability in water, while a strong distance-decay relationship was found in sediment. Further, cross-kingdom microbial network analysis revealed strong modular associations of bacteria and microeukaryotes, meanwhile, microeukaryotic habitat specialists might be keystone, but generalists have higher proportion of connections in the networks. This study provides significant insights into the response of bacteria and microeukaryotes to different urban pollutions between water and sediment, and the ecological processes structuring microbial community dynamics across habitat types under anthropogenic disturbances.

Performance Assessment of Natural Wastewater Treatment Plants by Multivariate Statistical Models: A Case Study

Waste stabilization ponds (WSPs) as natural wastewater treatment plants are commonly utilized for wastewater treatment due to their simple design, low cost, and low-skilled operator requirements. Large-scale studies assessing the performance of WSPs using multivariate statistical models are scarce. Therefore, this study was conducted to assess the performance of 16 full-scale WSPs regarding physicochemical parameters, algae, bacterial indicators, and pathogens (e.g., Cryptosporidium, Entamoeba histolytica) by using multivariate statistical models. The principal component analysis revealed that the chemical pollutants were removed significantly (p < 0.001) through the treatment stages of 16 WSPs, indicating that the treatment stages made a substantial change in the environmental parameters. The non-multidimensional scale analysis revealed that the treatment stages restructured the bacterial indicators significantly (p < 0.001) in the WSPs, implying that the bacterial indicators were removed with the progress of the treatment processes. The algal community exhibited a distinct pattern between the geographical location (i.e., upper WSPs versus lower WSPs) and different treatment stages (p < 0.001). Four out of the sixteen WSPs did not comply with the Egyptian ministerial decree 48/1982 for discharge in agriculture drainage; three of these stations are in lower Egypt (M.K., Al-Adlia, and Ezbet El-Borg), and one is in upper Egypt (Armant). The continuous monitoring of WSPs for compliance with regulatory guidelines with the aid of multivariate statistical models should be routinely performed.

Application of Organic Fertilizer Changes the Rhizosphere Microbial Communities of a Gramineous Grass on Qinghai–Tibet Plateau

The effects of organic fertilizer application on the soil microbial community in grassland systems have been extensively studied. However, the effects of organic fertilizers on the structure of rhizosphere microbial communities are still limited. In this study, the diversity and composition of rhizosphere microbial communities of a gramineous grass Elymus nutans under organic fertilizer treatment were studied in an artificial pasture on Qinghai–Tibet Plateau. After a growing season, the application of organic fertilizer not only increased the height and biomass of Elymus nutans, but also changed the rhizosphere microbial compositions. In particular, organic fertilizer increased the diversity of rhizosphere bacterial community and inhibited the growth of pathogenic bacteria such as Acinetobacter, but the opposite trend was observed for the diversity of fungal community. The assembly process of fungal community was changed from a stochastic process to a deterministic process, indicating that selection was strengthened. Additionally, both the infection rate of arbuscular mycorrhizal fungi (AMF) toward host plants and the development of AMF-related structures were significantly increased after the application of organic fertilizer. Our study demonstrated that the addition of organic fertilizer to artificial pasture could improve the growth of grass through the alteration of the rhizosphere microbial communities. Organic fertilizer had a greater selectivity for the bacterial and the fungal communities that enhanced the niche filtration in this community, further benefiting the yield of forages.

Domestic wastewater causes nitrate pollution in an agricultural watershed, China

Excessive quantities of nitrates in the aquatic environment can cause eutrophication and raise water safety concerns. Therefore, identification of the sources of nitrate is crucial to mitigate nitrate pollution and for better management of the water resources. Here, the spatiotemporal variations and sources of nitrate were investigated by stable isotopes (δ¹⁵N and δ¹⁸O), hydrogeochemical variables (e.g., NO₃^- and Cl^-), and exogenous microbial signals (i.e., sediments, soils, domestic and swine sewage) in an agricultural watershed (Changle River watershed) in China. The concentration ranges of δ¹⁵N- and δ¹⁸O-NO₃^- between 3.03‰-18.97‰ and -1.55‰-16.47‰, respectively, suggested that soil nitrogen, chemical fertilizers, and manure and sewage (M&S) were the primary nitrate sources. Bayesian isotopic mixing model suggested that the major proportion of nitrate within the watershed (53.12 ± 10.40% and 63.81 ± 15.08%) and tributaries (64.43 ± 5.03% and 76.20 ± 4.34%) were contributed by M&S in dry and wet seasons, respectively. Community-based microbial source tracking (MST) showed that untreated and treated domestic wastewater was the major source (>70%) of river microbiota. Redundancy analysis with the incorporation of land use, hydrogeochemical variables, dual stable isotope, and exogenous microbial signals revealed domestic wastewater as the dominant cause of nitrate pollution. Altogether, this study not only identifies and quantifies the spatiotemporal variations in nitrate sources in the study area but also provides a new analytical framework by combining nitrate isotopic signatures and community-based MST approaches for source appointment of nitrate in other polluted watersheds.

Distinct strategies of the habitat generalists and specialists in sediment of Tibetan lakes

Microbial metacommunities normally comprise generalists and specialists. Uncovering the mechanisms underlying the diversity patterns of these two sub-communities is crucial for aquatic biodiversity maintenance. However, little is known about the ecological assembly processes and co-occurrence patterns of the habitat generalists and specialists across large spatial scales in plateau lake sediments, particularly regarding their environmental adaptations. Here, we investigated assembly processes of the habitat generalists and specialists in sediment of Tibetan lakes and their role in the stability of metacommunity co-occurrence network. Our results showed that the habitat generalists exhibited broader environmental thresholds and closer phylogenetic clustering than specialist counterparts. In contrast, the specialists exhibited stronger phylogenetic signals of ecological preferences compared with the habitat generalists. Stochastic processes dominated the habitat generalist (63.2%) and specialist (81.3%) community assembly. Sediment pH was the major factor mediating the balance between stochastic and deterministic processes in the habitat generalists and specialists. In addition, revealed by network analysis, the habitat specialists played a greater role in maintaining the stability of metacommunity co-occurrence network. The insights gained from this study can be helpful to understand the mechanisms underlying maintenance of sediment microbial diversity in plateau lakes. This article is protected by copyright. All rights reserved.

Profound Change in Soil Microbial Assembly Process and Co-occurrence Pattern in Co-inoculation of Bradyrhizobium japonicum 5038 and Bacillus aryabhattai MB35-5 on Soybean

Rhizosphere microbial communities are vital for plant growth and soil sustainability; however, the composition of rhizobacterial communities, especially the assembly process and co-occurrence pattern among microbiota after the inoculation of some beneficial bacteria, remains considerably unclear. In this study, we investigated the structure of rhizomicrobial communities, their assembly process, and interactions contrasting when Bradyrhizobium japonicum 5038 and Bacillus aryabhattai MB35-5 are co-inoculated or Bradyrhizobium japonicum 5038 mono-inoculated in black and cinnamon soils of soybean fields. The obtained results indicated that the Chao and Shannon indices were all higher in cinnamon soil than that in black soil. In black soil, the co-inoculation increased the Shannon indices of bacteria comparing with that of the mono-inoculation. In cinnamon soil, the co-inoculation decreased the Chao indices of fungi comparing with that of mono-inoculation. Compared with the mono-inoculation, the interactions of microorganisms of co-inoculation in the co-occurrence pattern increased in complexity, and the nodes and edges of co-inoculation increased by 10.94, 40.18 and 4.82, 16.91% for bacteria and fungi, respectively. The co-inoculation of Bradyrhizobium japonicum 5038 and Bacillus aryabhattai MB35-5 increased the contribution of stochastic processes comparing with Bradyrhizobium japonicum 5038 inoculation in the assembly process of soil microorganisms, and owing to the limitation of species diffusion might restrict the direction of pathogenic microorganism movement. These findings support the feasibility of rebuilding the rhizosphere microbial system via specific microbial strain inoculation and provide evidence that the co-inoculation of Bradyrhizobium japonicum 5038 and Bacillus aryabhattai MB35-5 can be adopted as an excellent compound rhizobia agent resource for the sustainable development of agriculture.

Tracking microeukaryotic footprint in a peri-urban watershed, China through machine-learning approaches

Microeukaryotes play a significant role in biogeochemical cycling and can serve as bioindicators of water quality in freshwater ecosystems. However, there is a knowledge gap on how freshwater microeukaryotic communities are assembled, especially that how terrestrial microeukaryotes influence freshwater microeukaryotic assemblages. Here, we used a combination of 18S rRNA gene amplicon sequencing and community-based microbial source tracking (MST) approaches (i.e., SourceTracker and FEAST) to assess the contribution of microeukaryotes from surrounding environments (i.e., soils, river sediments, swine wastewater, influents and effluents of decentralized wastewater treatment plants) to planktonic microeukaryotes in the main channel, tributaries and reservoir of a peri-urban watershed, China in wet and dry seasons. The results indicated that SAR (~ 49% of the total communities), Opithokonta (~ 34%), Archaeplastida (~ 9%), and Amoebozoa (~ 2%) were dominant taxa in the watershed. The community-based MST analysis revealed that sewage effluents (7.96 - 21.84%), influents (2.23 - 13.97%), and river sediments (2.56 - 11.71%) were the major exogenous sources of riverine microeukaryotes. At the spatial scale, the downstream of the watershed (i.e., main channel and tributaries) received higher proportions of exogenous microeukaryotic OTUs compared to the upstream reservoirs, while at the seasonal scale, the sewage effluents and influents contributed higher exogenous microeukaryotes to river water in wet season than in dry season. Moreover, the swine and domestic wastewater led to the presence of Apicomplexa in wet season only, implying rainfall runoff may enhance the spread of parasitic microeukaryotes. Taken together, our study provides novel insights into the immigration patterns of microeukaryotes and their dominant supergroups between terrestrial and riverine habitats.

Pathogens Removal in a Sustainable and Economic High-Rate Algal Pond Wastewater Treatment System

This study evaluates the efficiency of a sustainable technology represented in an integrated pilot-scale system, which includes a facultative pond (FP), a high-rate algal pond (HRAP), and a rock filter (RF) for wastewater treatment to produce water that complies with the Egyptian standards for treated wastewater reuse. Still, limited data are available on pathogen removal through HRAP systems. Thus, in this study, the performance of the integrated system was investigated for the removal of Escherichia coli (E. coli), coliform bacteria, eukaryotic pathogens (Cryptosporidium spp., Giardia intestinalis, and helminth ova), somatic coliphages (SOMCPH), and human adenovirus (HAdV). Furthermore, physicochemical parameters were determined in order to evaluate the performance of the integrated system. The principal component analysis and non-metric multidimensional scaling analysis showed a strong significant effect of the integrated system on changing the physicochemical and microbial parameters from inlet to outlet. The mean log10 removal values for total coliform, fecal coliform, and E. coli were 5.67, 5.62, and 5.69, respectively, while 0.88 log10 and 1.65 log10 reductions were observed for HAdV and SOMCPH, respectively. The mean removal of Cryptosporidium spp. and Giardia intestinalis was 0.52 and 2.42 log10, respectively. The integrated system achieved 100% removal of helminth ova. The results demonstrated that the system was able to improve the chemical and microbial characteristics of the outlet to acceptable levels for non-food crops irrigation. Such findings together with low operation and construction costs of HRAPs should facilitate wider implementation of these nature-based systems in remote and rural communities. Overall, this study provides a novel insight into the performance of such systems to eliminate multiple microbial pathogens from wastewater.

DNA metabarcoding reveals the significant influence of anthropogenic effects on microeukaryotic communities in urban waterbodies

Biological monitoring and assessment are the first and most fundamental steps towards diagnosing ecological or environmental quality. Increasing anthropogenic impact on urban ecosystems has prompted the development of less expensive and more efficient bioassessment approaches. Generally, a morphospecies based approach is effective for plants and large organisms but challenging for the microbial biosphere. To overcome this challenge, we used high-throughput DNA sequencing for predicting anthropogenic effects on microeukaryotic communities in urban waterbodies along a pollution gradient in Wuhan City, central China in summer 2019. Our results indicated that microeukaryotic community structure was distinct between non-urban polluted reservoir and urban polluted waterbodies. The heterogeneity of environmental condition significantly affected the microeukaryotic diversity, community structure, and species interactions. Integrated co-occurring network analysis revealed that the pollution gradient has a significant adverse impact on network complexity and network dissimilarity. These results revealed that the significant variation in anthropogenically-driven environmental condition shaped microeukaryotic communities in urban freshwater ecosystems. Furthermore, we observed that the relative abundance of indicative OTUs were significantly and negatively correlated with pollution level and these indicative OTUs could be used to predict the water quality status with up to 77% success. Thus, our multiple approaches combining 18S rDNA amplicon sequencing, co-occurring network and indicator species analyses suggest that this study gives a novel approach based on microeukaryotic communities to assess and predict the water quality status of urban aquatic environments.

The ecology of the plastisphere: Microbial composition, function, assembly, and network in the freshwater and seawater ecosystems

Microplastics provide a unique habitat for microorganisms, forming the plastisphere. Yet the ecology of the plastisphere, including the microbial composition, functions, assembly processes, and interaction networks, needs to be understood. Here, we collected microplastics and their surrounding water samples in freshwater and seawater ecosystems. The bacterial and fungal communities of the plastisphere and the aquatic environment were studied based on 16S and internal transcribed spacer (ITS) high-throughput sequencing. We found that the plastisphere had a distinct microbial community and recruited a noteworthy proportion of unique species compared to the aquatic environment community, potentially altering ecosystem microbial community and causing microbial invasion. Using a random-forest machine-learning model, we identified a group of biomarkers that could best distinguish the plastisphere from the aquatic environment. Significant differences exist in microbial functions between the plastisphere and the aquatic environment, including functions of pathogenicity, compound degradation, as well as functions related to the cycling of carbon, nitrogen, and sulfur. And these functional differences were expressed differently in freshwater and seawater ecosystems. The oxidation-reduction potential, salinity, the concentrations of nitrogen-related ions (NO₃^-, NO₂^-, and NH₄⁺), and the concentration of dissolved organic carbon in the surrounding environment drive the variation of the plastisphere. But environmental physicochemical properties explain less of the microbial community variation in the plastisphere than that in the aquatic environment. Niche-based processes govern the assembly of the plastisphere community, while neutral-based processes dominate the community assembly of the aquatic environment. Furthermore, compared to the aquatic environment, the plastisphere has a network of less complexity, more modules, higher modularity, and more competitive links in freshwater ecosystems, but the pattern is reversed in seawater ecosystems. Altogether, the microbial ecology of the new anthropogenic ecosystem-plastisphere-is unique and exerts different effects in freshwater and seawater ecosystems.

The spatial distribution of the photosynthetic picoeukaryotes community structure in Lake Hongze

The spatial dynamics of picophytoplankton were investigated by flow cytometry and high-throughput sequencing in Lake Hongze, a large river-connecting lake. Picophytoplankton were mainly composed of phycocyanin-rich picocyanobacteria (PCY) and photosynthetic picoeukaryotes (PPEs). Picocyanobacteria was the dominant picophytoplankton group since the contribution of PPEs to total picophytoplankton was only 11.78%. However, PPEs were highly diverse and were composed of Chlorophyta, Bacillariophyta and Chrysophyceae. Environmental factors showed spatial differences, particularly in total phosphorus (TP), suspended solids (SS) and chemical oxygen demand (CODMn), which showed relatively high concentrations around the river channel. The abundances of PPEs and PCY showed similar spatial patterns, which were relatively low in the river course since they were negatively related to SS and CODMn. The top 10 OTUs contributed 79.18% of the total PPEs reads and affiliated with main species in PPEs. CCA results showed that, PPEs community composition was significantly impacted by temperature and DO at sites away from river channel, while was only influenced by nitrite at sites around the river channel.

Changes in protist communities in drainages across the Pearl River Delta under anthropogenic influence

Drainages in the Pearl River Delta urban agglomeration (PRDUA) host vital aquatic ecosystems and face enormous pressures from human activities in one of the largest urban agglomerations in the world. Despite being crucial components of aquatic ecosystems, the interactions and assembly processes of the protistan community are rarely explored in areas with serious anthropogenic disturbance. To elucidate the mechanisms of these processes, we used environmental DNA sequencing of 18S rDNA to investigate the influence of environmental factors and species interactions on the protistan community and its assembly in drainages of the PRDUA during summer. The protistan community showed a high level of diversity and a marked spatial pattern in this region. Community assembly was driven primarily by stochastic processes based on the Sloan neutral community model, explaining 74.28%, 75.82%, 73.67%, 74.40% and 51.24% of community variations in the BJ (Beijiang), XJ (Xijiang), PRD (Pearl River Delta), PRE (Pearl River Estuary) areas and in total, respectively. Meanwhile, environmental variables including temperature, pH, dissolved oxygen, transparency, nutrients and land use were strongly correlated with the composition and assembly of the protistan community, explaining 40.40% of variation in the protistan community. Furthermore, the bacterial community was simultaneously analysed by the 16S rDNA sequencing. Co-occurrence network analysis revealed that species interactions within bacteria (81.41% positive) or protists (82.80% positive), and those between bacteria and protists (50% positive and 50% negative) impacted the protistan community assembly. In summary, stochastic processes dominated, whereas species interactions and environmental factors also played important roles in shaping the protistan communities in drainages across the PRDUA. This study provides insights into the ecological patterns, assembly processes and species interactions underlying protistan dynamics in urban aquatic ecosystems experiencing serious anthropogenic disturbance.

Micropollutant biotransformation and bioaccumulation in natural stream biofilms

Micropollutants are ubiquitously found in natural surface waters and pose a potential risk to aquatic organisms. Stream biofilms, consisting of bacteria, algae and other microorganisms potentially contribute to bioremediating aquatic environments by biotransforming xenobiotic substances. When investigating the potential of stream biofilms to remove micropollutants from the water column, it is important to distinguish between different fate processes, such as biotransformation, passive sorption and active bioaccumulation. However, due to the complex nature of the biofilm community and its extracellular matrix, this task is often difficult. In this study, we combined biotransformation experiments involving natural stream biofilms collected up- and downstream of wastewater treatment plant outfalls with the QuEChERS extraction method to distinguish between the different fate processes. The QuEChERS extraction proved to be a suitable method for a broad range of micropollutants (> 80% of the investigated compounds). We found that 31 out of 63 compounds were biotransformed by the biofilms, with the majority being substitution-type biotransformations, and that downstream biofilms have an increased biotransformation potential towards specific wastewater-relevant micropollutants. Overall, using the experimental and analytical strategy developed, stream biofilms were demonstrated to have a broad inherent micropollutant biotransformation potential, and to thus contribute to bioremediation and improving ecosystem health.