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Pressure treatment of Microcystis prior to discharge into the aquatic environment has been an emerging approach to relieve the Microcystis blooms. However, current literature has not noticed the changes of pressurized Microcystis on microbial community characteristics in water. We have evaluated the performance of variable pressure treatment protocols, and the most suitable case was proven as follows: pressuring Microcystis up to 0.7 MPa in 5 s at a pressure-accelerating speed of 0.14 MPa/s, and treating for 30 s. After treatment, the gas vesicles were efficiently destroyed and extracellular polymeric substance (EPS) on cells was exfoliated. The exfoliated EPS significantly affected phyla including Verrucomicrobiota associated with the degradation of organic matters, and thus affected community function, the energy metabolism was enhanced and uptake of dissolved organic phosphorus (DOP) by microorganisms increased after pressure treatment. This study was of significance for exploring the effects of pressurized Microcystis control measures on lake ecological environment. [Display omitted] • Different pressurized enforcement modes at 0.7 MPa on turbidity were determined. • Extracellular polymeric substance of Microcystis exfoliated after pressure treatment. • Pressure treatment temporarily reduced bacterial community diversity. • Bacterial abundance for degradation of organic matter increased after pressure. • Uptake of dissolved organic phosphorus by microorganisms increased after pressure treatment. [ABSTRACT FROM AUTHOR]

Once in aquatic ecosystems, plastics can be easily colonized by diverse microbes, and these microbial communities on plastics—the 'plastisphere'—often differ from the communities in the surrounding water and other substrates. However, our knowledge of plastic-associated bacterial and fungal communities on diverse plastics in freshwater is poor, especially for fungal communities. Furthermore, intraspecies interactions among bacterial and fungal communities colonized on diverse plastics are poorly known. Here, we characterized the taxonomic composition and diversity of bacteria and fungi on three types of plastics in a lab-scale incubator with freshwater from an urban river. High-throughput sequencing revealed that the alpha diversity of bacterial communities was higher on polyethylene microplastics (MPs) than on polyethylene (PE) and polypropylene (PP) sheets. The structure of bacterial communities on MPs differed from those on plastic sheets. In contrast, no striking differences in alpha diversity and taxonomic composition were observed for fungal communities on different types of plastics. Members of Ascomycota, Basidiomycota, Blastocladiomycota and Mucoromycota dominated fungal assemblages on plastics. Co-occurrence network analysis revealed that the biotic interactions between bacteria and fungi on MPs were less complex than those on PE and PP sheets. The three types of plastics shared no keystone taxa. The functional profiles (KEGG) predicted by Tax4Fun showed that the pathways of alanine, aspartate, glutamate and biotin metabolism were enriched in biofilms on MPs. Nonetheless, the higher complexity of plastic sheet-associated biofilms might make them more resistant to environmental perturbation and facilitate the maintenance of microbial activities. [Display omitted] • Alpha diversity of bacteria was higher in MP-attached biofilm than in PE and PP sheets. • Microbial community on MPs differed structurally from those on plastic sheets. • Connection/complexity of bacteria and fungi in MPs was lower than in plastic sheets. • Keystones species on diverse plastic debris were distinguishable and verified. • Metabolic pathways were altered in biofilms colonizing three types of plastics. [ABSTRACT FROM AUTHOR]

Abstract Black-odor phenomenon in highly urbanized river is increasingly recognized as a global ecological risk. Biotransformation associated with sulfur cycle is a major contributor to the blank-odor phenomenon. The vertical geochemical gradient in black-odor rivers is likely to alter microbial community assemblages and functions in the sulfur cycle. However, the interactions between geochemical gradients and microbial communities, as well as the changes in the process of sulfur biotransformation under different environmental conditions remain largely unknown. The vertical community assembly patterns and the impacts of microbial communities and genes on the biotransformation in the sulfur cycle were revealed in our study for the first time in a typical urban black-odor river, Jinchuan River, in China. Vertical beta-diversity patterns of microbial communities mainly resulted from species replacement that was largely driven by spatial turnover (β SIM = 0.43) but also influenced by nestedness (β NES = 0.08). MiSeq sequencing and GeoChip 5.0 microarray chip approaches were applied and identify 41 bacterial genera, 8 archaeal genera, and 26 genes involved in the sulfur cycle in Jinchuan River. The vertical beta-diversity patterns of microbial profile mainly resulted from species replacement. Those sulfur-related bacterial and archaeal genera, accounting for 23.15% and 42.65% of the total bacteria and archaea respectively in analysed samples, were mainly responsible for sulfur reduction. According to redundancy analysis, oxidation-reduction potential (r = −0.8662, P < 0.05), S2− concentration (r = −0.6288, P < 0.05), and total nitrogen concentration (r = −0.6782, P < 0.05) were identified as factors that significantly affect sulfur-related microbial communities. The highest reaction potential was detected in the dissimilated sulfate reduction action and experienced an increase with depth increasing in the river system. The results indicated that the sulfur biotransformation in a deeper layer in river sediment could make more contribution to the black-odor phenomenon in urban rivers. Graphical abstract Image 1 Highlights • Vertical structured microbial communities in an urban river were detected. • Functions of microbial community on sulfur biotransformation were detected. • Remarkable micro-scale differentiations were found in different depths of rivers. • Vertical microbial beta-diversity patterns were largely driven by spatial turnover. • Sulfur biotransformation in deeper sediment contributes more to river pollution. [ABSTRACT FROM AUTHOR]

Expanding the stress tolerance and adaptation potential of primary producers is of importance for the restoration and management of aquatic ecosystems. Microorganisms have been reported to mediate improved resistance toward different abiotic stresses of primary producers in terrestrial and marine ecosystems. However, it is not clear about the role of microbial communities in the turbidity resistance of primary producers, when aquatic ecosystems are under turbidity pressure. In this study, key microbes and the action path which enhance turbidity tolerance of primary producers were recognized by mesocosm and various multivariate statistical methods. Remarkable decrease of the biomass of primary producers was found with the increase of turbidity. Significant differences in microbial community under different turbidity pressure were recognized and key microbes which may expand the turbidity tolerance of primary producers were further identified. Rhodobacter and Rhodoferax were selected as key microbes by the investigation of keystone species in the microbial ecological network and significant discriminant taxa under different turbidity stress. The action path for microbial communities to help primary producers cope with turbidity pressure was found through structural equation model, and in which the increase of key microbes may expand the turbidity tolerance of primary producers through enhancing the microbial loop. The results may provide a new insight for aquatic ecosystems to resist turbidity stress, and provide a theoretical basis for the management and restoration of aquatic ecosystems. • Response of primary producers and microbial communities to turbidity was examined. • Key microbes that may expand turbidity tolerance of primary producers were identified. • The pathway that may enhance turbidity tolerance of primary producers was discerned. [ABSTRACT FROM AUTHOR]

• Enhanced nitrogen removal processes widely exist in river confluences. • Microbial community in confluences can sustain in downstream area. • Contributions of microorganism in confluences to lower reaches decrease with distance. • Confluence characteristics determine influence scope of microorganism in confluences. River confluences are crucial parts of the river networks, which connect different rivers and promote material exchange between them. Joining of two rivers would cause sharp shifts of flow dynamics and form confluence hydrodynamic zone (CHZ) with specific flow structure and biogeochemical processes. However, CHZs are small areas compared with river networks, whether and how the biogeochemical processes in CHZs would influence the lower reaches and even the whole river networks remain unclear. To address this gap, the present study focused on the nitrogen dynamics in a river network consisting a series of confluences, and combined molecular biological tools, gene-centric modelling approach and SourceTracker analysis to reveal the microorganisms induced nitrogen transformation processes in CHZs and other normal hydrodynamic zones (NHZs). Results illustrated that the enriched microbial species in CHZs were associated with nitrogen transformation, such as Terrimonas and Sphingobacterium , which were reported to be vital participants in nitrate and nitrite reduction processes. The reactions rates of different nitrogen transformation processes, calculated based on functional genes abundances, further revealed that N 2 production rates were significantly higher in CHZs than NHZs (p < 0.05), demonstrating CHZs were the hotspots for nitrogen removal in the researched river network. Besides, the specific microbial communities and stimulated nitrogen removal processes in CHZ would sustain in lower reaches. SourceTracker analysis illustrated that microbial communities would exert significant influences on lower reaches, and the influence scope was controlled by confluences characteristics, such as flow ratio between tributary and main stream. Higher discharge ratio would increase the influence scope of microbial community in CHZ. These results indicate that reasonable design of confluence characteristics can be applied as a critical engineering measure for the improvement of ecological health of river networks. [ABSTRACT FROM AUTHOR]

Prioritizing the relationship between heterogeneity of sediment habitats and river bends is critical when planning and reconstructing urban rivers. However, the exact relationship between ecological heterogeneity and river bends remains ambiguous. Therefore, this research proposed a new approach to quantify and predict bend-induced ecological heterogeneity, incorporating the bacteria-based index of biotic integrity (Ba-IBI), path model, and random forest regression model. The developed Ba-IBI quantified heterogeneity in sediment microbial communities, ranging from low (1.40) to high (3.97). A path model was developed and validated in order to further investigate the relative contributions of environmental factors to the Ba-IBI. The established path model, which was considered acceptable with a CMIN/df = 1.949 < 4, suggested that primary environmental factors affecting the sediment bacterial communities were flow velocity and ammonium concentration in sediment. To further characterize the relationship between environmental factors and the Ba-IBI, a function was constructed using the random forest regression model that predicts the responses of sediment bacterial communities to environmental factors with R2 = 0.6126. The proposed approach and prediction tools will provide knowledge to improve natural channel design and post-project evaluations in river restoration projects. [Display omitted] • A novel way for the identification of ecological heterogeneity was established. • Ba-IBI scores revealed a significant difference between straight and bent channels. • Ba-IBI score was influenced by flow velocity, particle size and NH 4 +-N in sediment. • A function reflecting habitat heterogeneity with environmental paraments was found. [ABSTRACT FROM AUTHOR]

[Display omitted] • Computational models can capture microbial dynamics in different ecosystems. • Hydrodynamic processes are vital for applying microbial models to aquatic ecosystems. • Ecological models focus on associations of multiple members in the community. • Metabolic models aim to simulate dynamic processes of functional species. Microbial communities are essential roles in aquatic ecosystems, which participate in a number of biogeochemical processes, and are vital for the protection and ecological remediation of water environment. Mathematical models have been demonstrated to be highly advantageous for investigating the composition, functions and metabolic behaviors of microbial community. Moreover, advances in molecular biology tools have provided sufficient information for numerical simulation of microbial community structure and dynamics, which contribute to the rapid developments of microbial modelling approaches. However, models focusing only on the metabolic processes of microbial community exist nonnegligible drawbacks when applying in aquatic ecosystems. They are not capable to simulate the hydrodynamic processes in flowing water, which would significantly change the composition and functions of microbial community. Thus, incorporating hydrodynamic processes into microbial models are vital for the in-depth investigation of aquatic microbial community. In this review, latest developments on microbial modelling approaches have been summarized to demonstrate how different approaches have been adapted to highly dynamic context to unravel the characteristics of microbial community in the aquatic ecosystems. Furthermore, present limitations of different modelling strategies have been discussed and several future development directions have been provided to make the simulation of microbial community in aquatic ecosystem to greater depth and accuracy. [ABSTRACT FROM AUTHOR]

• Biomarkers of the plastisphere were identified by random-forest machine learning. • Environmental drivers of the plastisphere community variation were explored. • The plastisphere could cause different ecological impacts in different ecosystems. • Niche-based processes govern the assembly of the plastisphere microbial community. • The plastisphere plays a diverse role in microbial networks in different 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 (NO 3 −, NO 2 −, and NH 4 +), 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Phosphorus, one of the primary limiting factors for eutrophication, plays a crucial role in the ecology health of aquatic ecosystems. However, understanding phosphorus bioavailability and source contributions in contaminated lake sediments which could help develop effective eutrophication management plans is limited largely due to the lack of appropriate methods in large catchments with a complex arrangement of sources. Based on the significant relationships between sediment, phosphorus and microbial community, source-specific microbial community fingerprints formed by machine-learning classification SourceTracker might shed light on determining dominant phosphorus sources in the river-lake systems in the era of high-throughput sequencing. This study was conducted in Dongting Lake that suffered accelerated eutrophication due to considerable phosphorus input from the inflow-rivers. The results of phosphorus fractionation according to the Standards, Measurements and Testing harmonized procedure indicated that sediments in the central lake had a higher concentration of non-apatite inorganic phosphorus (Mann-Whitney U test), which deserves greater attention on the risk of phosphorus release. The significant relationships between phosphorus fractionations, sediment and bacterial community were established with the spearman correlation and network analysis. SourceTracker analysis indicated that the major inflow-rivers of phosphorus sources to Dongting Lake were the Songzi, Miluo, and Xinqiang Rivers. The effects of sediment diffusion distance on phosphorus source apportionment were further confirmed. Taken together, our results contribute to an improved understanding of phosphorus fractionations and source contributions in the river-lake systems and its potential impact to eutrophication management plans. • A new approach for tracing phosphorus in river-lake systems was established. • Phosphorus bioavailability was evaluated by phosphorus fractionation in sediments. • Significant correlations between sediment, phosphorus and microbial community were determined. • Impacts of sediment dynamics on phosphorus source apportionment were verified. • The dominant inflow-rivers of phosphorus sources to Dongting Lake were determined. [ABSTRACT FROM AUTHOR]

Understanding the differences of biogeochemical processes between straight and bent channel is important for weighting them in urban river planning and reconstruction. Shifts in the assembly of the sediment microbial community of bent channels are key, but understudied, component of bend-induced increases in biogeochemical reaction rates. Here, the assembly of microbial community and its feedback to nitrogen transformation in urban river bends were firstly studied by coupling ecological theory, aqueous biogeochemistry, DNA sequencing, and hydrodynamic profiling. It was found that the sediment particle size was the main driving force for producing the significant difference of microbial community structure in river bends. Homogeneous selection, quantified by β-nearest taxon index (βNTI), emerged in the urban river bends and accounted for 79.2% of all ecological processes. Moreover, a significant positive relationship between βNTI and the sediment particle size indicated that shifts in particle size were associated with shifts in deterministic selective pressures, which govern the composition of the microbial community. The significant correlation between the βNTI and changes in nitrate concentration also indicated that nitrate leads to deterministic processes, which select microbial taxa. These microbial taxa which are governed by deterministic processes show specific nitrogen transformation traits, and react on the nitrate concentration. A multiphase transport model allowed the separation of the effects of deterministic processes on nitrogen concentration from measured concentration influenced by complex biogeochemical processes. The results indicated that both the ammonia transformation and microbial nitrogen removal were stimulated in coarse sediment regions of the river bends, and were confirmed by abundant differences of microbial taxa that could promote ammoxidation and denitrification. The coarse sediment benefits microbial nitrogen removal in urban river bends, a discovery that should inform urban river reconstruction designs and the efforts to assess the environmental water capacity of urban rivers. Image 1 • Microbial community distribution and assembly in urban river bends was analyzed. • Sediment particle size governs microbial community distribution in the river bends. • Microbial community affects nitrogen transformation by deterministic processes. • Microbial nitrogen removal in coarse sediment region of river bends was enhanced. [ABSTRACT FROM AUTHOR]

River confluences result in mixture and transformation of dissolved organic matter (DOM), influencing the phylogeny of microbial community, furthermore, the integrity and function of river systems. The relationship between the microbial community and DOM is complex, especially in the confluence zone. Previous reports focused on shifts in the different bacterial community in response to exposure to the same terrestrial DOM. However, the transformation of bacterial community induced by convergent DOM remains unknown. This study showed the shifts of DOM components at the junction via excitation–emission matrices parallel factor analysis. Metabolic differences were also determined via phylogenetic investigation of communities by reconstruction of unobserved states. The results demonstrated a direct link between the microbial metabolism and DOM biodegradation during the heterotrophic process. In response to diverse DOM conditions, the taxonomic composition and metabolic function of the microbial community presented significant differences. Different taxa may be involved in metabolizing various DOM components. As indicative bacteria that are closely associated with DOM components, Proteobacteria (Sphingomonas) are significant for microbial utilization and were important during the DOM-degrading process. Compared with other conditions, the abundance of carbon metabolism was higher in convergences where urban rivers joined with estuary or source water. Furthermore, humic-like DOM, converging in the confluence zone, induced a more active lipid metabolism. This study applied techniques that capture the diversity and complexity of bacterial communities and DOM, and provides new insight on the basis of the interaction between bacterial communities and DOM in confluence processes of biogeochemical significance. Image 1 • Proteobacteria showed high connectivity with humic-like DOM. • Sphingomonas were significant at various confluences in urban areas. • Humic-like DOM converge could induce a more active lipid metabolism. • The Carbon metabolism was active when rivers joined with estuary or source water. [ABSTRACT FROM AUTHOR]