Seasonal variation in the bacterial community composition of a large estuarine reservoir and response to cyanobacterial proliferation

Multivariate statistical and bioinformatic analyses for the seasonal variations of actinobacterial community structures in a drinking water reservoir

Actinobacterial community is a conspicuous part of aquatic ecosystems and displays an important role in the case of biogeochemical cycle, but little is known about the seasonal variation of actinobacterial community in reservoir ecological environment. In this study, the high-throughput techniques were used to investigate the structure of the aquatic actinobacterial community and its inducing water quality parameters in different seasons. The results showed that the highest diversity and abundance of actinobacterial community occurred in winter, with Sporichthya (45.42%) being the most abundant genus and Rhodococcus sp. (29.32%) being the most abundant species. Network analysis and correlation analysis suggested that in autumn the dynamics of actinobacterial community were influenced by more factors and Nocardioides sp. SX2R5S2 was the potential keystone species which was negatively correlated with temperature (R = -0.72, P < 0.05). Changes in environmental factors could significantly affect the changes in actinobacterial community, and the dynamics of temperature, dissolved oxygen (DO), and turbidity are potential conspicuous factors influencing seasonal actinobacterial community trends. The partial least squares path modeling further elucidated that the combined effects of DO and temperature not only in the diversity of actinobacterial community but also in other water qualities, while the physiochemical parameters (path coefficient = 1.571, P < 0.05) was strong environmental factors in natural mixture period. These results strengthen our understanding of the dynamics and structures of actinobacterial community in the drinking water reservoirs and provide scientific guidance for further water quality management and protection in water sources.

Deciphering characterization of seasonal variations in microbial communities of marine ranching: Diversity, co-occurrence network patterns, and assembly processes

Offshore coastal marine ranching ecosystems are one of the most productive ecosystems. The results showed that the composition and structure of the microbial communities varied considerably with the season. Co-occurrence network analysis demonstrated that the microbial network was more complex in summer and positively correlated links (cooperative or symbiotic) were dominated in autumn and winter. Null model indicated that the ecological processes of the bacterial communities were mainly governed by deterministic processes (mainly homogeneous selection) in summer. For microeukaryotic communities, assembly processes were more regulated by stochastic processes in all seasons. For rare taxa, assembly processes were regulated by stochastic processes and were not affected by seasonality. Changes in water temperature due to seasonal variations were the main, but not the only, environmental factor driving changes in microbial communities. This study will improve the understanding of offshore coastal ecosystems through the perspective of microbial ecology.

Nonpoint Source Pollution (NPSP) Induces Structural and Functional Variation in the Fungal Community of Sediments in the Jialing River, China

Nonpoint source pollution (NPSP) from human production and life activities causes severe destruction in river basin environments. In this study, three types of sediment samples (A, NPSP tributary samples; B, non-NPSP mainstream samples; C, NPSP mainstream samples) were collected at the estuary of the NPSP tributaries of the Jialing River. High-throughput sequencing of the fungal-specific internal transcribed spacer (ITS) gene region was used to identify fungal taxa. The impact of NPSP on the aquatic environment of the Jialing River was revealed by analysing the community structure, community diversity, and functions of sediment fungi. The results showed that the dominant phylum of sediment fungi was Rozellomycota, followed by Ascomycota and Basidiomycota (relative abundance > 5%). NPSP caused a significant increase in the relative abundances of Exosporium, Phialosimplex, Candida, Inocybe, Tausonia, and Slooffia, and caused a significant decrease in the relative abundances of Cercospora, Cladosporium, Dokmaia, Setophaeosphaeria, Paraphoma, Neosetophoma, Periconia, Plectosphaerella, Claviceps, Botrytis, and Papiliotrema. These fungal communities therefore have a certain indicator role. In addition, NPSP caused significant changes in the physicochemical properties of Jialing River sediments, such as pH and available nitrogen (AN), which significantly increased the species richness of fungi and caused significant changes in the fungal community β-diversity (P < 0.05). pH, total phosphorus (TP), and AN were the main environmental factors affecting fungal communities in sediments of Jialing River. The functions of sediment fungi mainly involved three types of nutrient metabolism (symbiotrophic, pathotrophic, and saprotrophic) and 75 metabolic circulation pathways. NPSP significantly improved the pentose phosphate pathway, pentose phosphate pathway, and fatty acid beta-oxidation V metabolic circulation pathway functions (P < 0.05) and inhibited the chitin degradation to ethanol, super pathway of heme biosynthesis from glycine, and adenine and adenosine salvage III metabolic circulation pathway functions (P < 0.05). Hence, NPSP causes changes in the community structure and functions of sediment fungi in Jialing River and has adversely affected for the stability of the Jialing River Basin ecosystem.

Core and conditionally rare taxa as indicators of agricultural drainage ditch and stream health and function

BACKGROUND

The freshwater microbiome regulates aquatic ecological functionality, nutrient cycling, pathogenicity, and has the capacity to dissipate and regulate pollutants. Agricultural drainage ditches are ubiquitous in regions where field drainage is necessary for crop productivity, and as such, are first-line receptors of agricultural drainage and runoff. How bacterial communities in these systems respond to environmental and anthropogenic stressors are not well understood. In this study, we carried out a three year study in an agriculturally dominated river basin in eastern Ontario, Canada to explore the spatial and temporal dynamics of the core and conditionally rare taxa (CRT) of the instream bacterial communities using a 16S rRNA gene amplicon sequencing approach. Water samples were collected from nine stream and drainage ditch sites that represented the influence of a range of upstream land uses.

RESULTS

The cross-site core and CRT accounted for 5.6% of the total number of amplicon sequence variants (ASVs), yet represented, on average, over 60% of the heterogeneity of the overall bacterial community; hence, well reflected the spatial and temporal microbial dynamics in the water courses. The contribution of core microbiome to the overall community heterogeneity represented the community stability across all sampling sites. CRT was primarily composed of functional taxa involved in nitrogen (N) cycling and was linked to nutrient loading, water levels, and flow, particularly in the smaller agricultural drainage ditches. Both the core and the CRT were sensitive responders to changes in hydrological conditions.

CONCLUSIONS

We demonstrate that core and CRT can be considered as holistic tools to explore the temporal and spatial variations of the aquatic microbial community and can be used as sensitive indicators of the health and function of agriculturally dominated water courses. This approach also reduces computational complexity in relation to analyzing the entire microbial community for such purposes.

Spatiotemporal Shift of T4-Like Phage Community Structure in the Three Largest Estuaries of China

Estuaries are one of the most highly productive and economically important ecosystems at the continent-ocean interface. Estuary productivity is largely determined by the microbial community structure and activity. Viruses are major agents of microbial mortality and are key drivers of global geochemical cycles. However, the taxonomic diversity of viral communities and their spatial-temporal distribution in estuarine ecosystems have been poorly studied. In this study, we investigated the T4-like viral community composition at three major Chinese estuaries in winter and in summer. Diverse T4-like viruses, which were divided into three main clusters (Clusters I to III), were revealed. The Marine Group of Cluster III, with seven identified subgroups, was the most dominant (averaging 76.5% of the total sequences) in the Chinese estuarine ecosystems. Significant variations of T4-like viral community composition were observed among estuaries and seasons, with higher diversity occurring in winter. Among various environmental variables, temperature was a main driver of the viral communities. This study demonstrates viral assemblage diversification and seasonality in Chinese estuarine ecosystems. IMPORTANCE Viruses are ubiquitous but largely uncharacterized members of aquatic environments that cause significant mortality in microbial communities. Recent large-scale oceanic projects have greatly advanced our understanding of viral ecology in marine environments, but those studies mostly focused on oceanic regions. There have yet to be spatiotemporal studies of viral communities in estuarine ecosystems, which are unique habitats that play a significant role in global ecology and biogeochemistry. This work is the first comprehensive study that provides a detailed picture of the spatial and seasonal variation of viral communities (specifically, T4-like viral communities) in three major estuarine ecosystems in China. These findings provide much-needed knowledge regarding estuarine viral ecosystems, which currently lags in oceanic ecosystem research.

Review: Current understanding on biological filtration for the removal of microcystins

Harmful algal blooms (HABs) have become a global problem not only in aquatic habitats but also in public health and safety due to the production of cyanotoxins as their secondary metabolites. Among the various identified cyanotoxin groups, microcystins (MCs) are one of the most prevalent cyanotoxin detected during HABs. Different strategies including advanced physical and chemical treatment processes have been developed to mitigate the threat of cyanotoxins in water utilities, but these have revealed certain limitations in terms of high operational costs, low removal efficacy, and harmful by-products formation. Recently, biological filtration systems (BFS) have gained attention for safe drinking water production as they can treat various natural organic matter (NOM) and emerging contaminants through a highly efficient and environmentally sustainable process. However, limited attention has been given to understand the current research progress, research challenges, and knowledge gaps for the successful implementation of BFS for MC removal. Therefore, in this review, currently identified MC biodegradation pathways and MC-degrading microorganisms with their degradation rates are summarized, which may be pivotal for studying bioaugmented BFS to enhance the MC removal during HABs. Moreover, both laboratory and field studies on BFS for MC removal are reviewed, followed by a discussion of current challenges and future research needs for the practical application of BFS.

Response of bacterial communities and function to dissolved organic matters in groundwater contaminated by landfill leachate

The migration and transformation of dissolved organic matter (DOM) caused by landfill leachate leakage affected the phylogenetic development of bacterial communities in groundwater around the landfill. Previous studies mainly focused on the hydrochemical properties of DOM in groundwater contaminated by landfill leachate and the relationships between groundwater quality parameters and bacterial communities. However, the changes in DOM components and bacterial communities caused by landfill leachate leakage and their correlations remained unclear. In this work, we analyzed the evolution characteristics of DOM and identified the bacterial communities and their corresponding functions in groundwater around the landfill. The results showed that DOM content in groundwater increased after the diffusion of landfill leachate to groundwater. Significant differences in characteristics between DOM components were presented at different locations in the landfill leachate plume due to the physical dilution and bacterial degradation of DOM. One of the obvious manifestations was the tendency of humic acid-like substances to accumulate at downstream points. Samples from the contaminated aquifer had higher diversity and abundance of bacterial communities than those in the uncontaminated aquifer. Anaerobic or facultative anaerobic bacteria played predominant roles in contaminated groundwater, due to the input of organic matter, nitrate, and ammonia nitrogen. Redundancy analysis indicated that the content of fulvic acid-like DOM had a conspicuous impact on the composition of bacterial communities in the polluted groundwater. Vogesella were the dominant bacteria at the genus level in groundwater around the landfill. Furthermore, Vogesella were significant for microbial utilization and played an important role in the production of fulvic acid-like DOM. These results indicated that landfill leachate pollution posed a potential threat to the structure and function of bacterial communities in groundwater, and provided a basis for exploring the interaction between DOM composition and bacterial communities in groundwater plume contaminated by landfill leachate.

Water Quality and Microbial Community in the Context of Ecological Restoration: A Case Study of the Yongding River, Beijing, China

Ecological water replenishment via interbasin water diversion projects provides opportunities for ecological river restoration. Untangling water quality changes, microbiota dynamics, and community functions is necessary for sustainable ecological management. Using the Yongding River as a case study, we monitored the water quality and applied genomic sequencing to investigate microbial communities of the river in different stages after ecological water replenishment. Our results showed that river water quality represented by chemical oxygen demand (COD), total nitrogen (TN), and chlorophyll-a (Chl-a) did not change significantly during months after water replenishment. The bacterial community composition varied in different months and river subsections. The Cyanobium_PCC-6307, CL500-29 marine group, and Pseudomonas were dominant in the later stages after water replenishment. Water temperature, pH, and nutrient levels significantly affected the microbial community composition, and ecological restoration may have the potential to influence nitrogen cycling in the river. Our results can provide ecological insights into sustainable water quality maintenance and river management following ecological restoration enabled by ecological water replenishment.

Temporal heterogeneity of bacterial communities and their responses to Raphidiopsis raciborskii blooms

To elucidate the interspecies connectivity between cyanobacteria and other bacteria (noncyanobacteria), microbial diversity and composition were investigated through high-throughput sequencing (HTS) in a drinking water reservoir in Chongqing city, Southwest China, during Raphidiopsis raciborskii blooms. Significant temporal changes were observed in microbial community composition during the sampling period, primarily reflected by variations in relative bacterial abundance. The modularity analysis of the network demonstrated that the bacterial community forms co-occurrence/exclusion patterns in response to variations in environmental factors. Moreover, five modules involved in the dynamic phases of the R. raciborskii bloom were categorized into the Pre-Bloom, Bloom, Post-Bloom, and Non-Bloom Groups. The reservoir was eutrophic (i.e., the average concentrations of total nitrogen (TN) and total phosphorus (TP) were 2.32 and 0.07 mg L^-1, respectively) during the investigation; however, Pearson's correlation coefficient showed that R. raciborskii was not significantly correlated with nitrogen and phosphorus. However, other environmental factors, such as water temperature, pH, and the permanganate index, were positively correlated with R. raciborskii. Importantly, Proteobacteria (α-, γ-Proteobacteria), Acidobacteria, Chloroflexi, and Firmicutes were preferentially associated with increased R. raciborskii blooms. These results suggested that the transition of R. raciborskii bloom-related microbial modules and their keystone species could be crucial in the development and collapse of R. raciborskii blooms and could provide a fundamental basis for understanding the linkage between the structure and function of the microbial community during bloom dynamics.

Characterizing sediment bacterial community and identifying the biological indicators in a seawater-freshwater transition zone during the wet and dry seasons

Seawater intrusion has a detrimental effect on agriculture, industry, and human health. One question of particular interest is how the microbial community responds to and reflects seawater intrusion with seasonal variation. The current study explored the seasonal changes in bacterial community composition and interaction in the vicinity of Pearl River Estuary in dry season (January) and wet season (September). Results indicated that the salinity of sediment samples obtained in dry season was higher than that in wet season. The salt stress induced a declined alpha diversity but resulted in a loosely connected and unstable biotic interaction network in the bacterial communities. Random forest prediction and redundancy analysis of bacterial community indicated that salinity substantially affected the bacterial communities. Multiple lines of evidence, including the enrichment of bacterial taxa in the high-salinity location, microbe-microbe interactions, environment-microbe interactions, and machine learning approach, demonstrated that the families Moraxellaceae and Planococcaceae were the keystone taxa and were resistant to salt stress, which suggested that both of them can be used as potential biological indicators of monitoring and controlling seawater intrusion in coastal zone areas.

An Inducible Microbacterium Prophage vB_MoxS-R1 Represents a Novel Lineage of Siphovirus

Lytic and lysogenic infections are the main strategies used by viruses to interact with microbial hosts. The genetic information of prophages provides insights into the nature of phages and their potential influences on hosts. Here, the siphovirus vB_MoxS-R1 was induced from a Microbacterium strain isolated from an estuarine Synechococcus culture. vB_MoxS-R1 has a high replication capability, with an estimated burst size of 2000 virions per cell. vB_MoxS-R1 represents a novel phage genus-based genomic analysis. Six transcriptional regulator (TR) genes were predicted in the vB_MoxS-R1 genome. Four of these TR genes are involved in stress responses, virulence and amino acid transportation in bacteria, suggesting that they may play roles in regulating the host cell metabolism in response to external environmental changes. A glycerophosphodiester phosphodiesterase gene related to phosphorus acquisition was also identified in the vB_MoxS-R1 genome. The presence of six TR genes and the phosphorus-acquisition gene suggests that prophage vB_MoxS-R1 has the potential to influence survival and adaptation of its host during lysogeny. Possession of four endonuclease genes in the prophage genome suggests that vB_MoxS-R1 is likely involved in DNA recombination or gene conversion and further influences host evolution.

Spatiotemporal dynamics in microbial communities mediating biogeochemical cycling of nutrients across the Xiaowan Reservoir in Lancang River

Microbes drive biogeochemical cycles of nutrients controlling water quality in freshwater ecosystems, yet little is known regarding how spatiotemporal variation in the microbial community affects this ecosystem-level functional processes to resist perturbations. Here we examined spatiotemporal dynamics of microbial communities in paired stratified water columns and sediments collected from the Xiaowan Reservoir of Lancang-Mekong River over a year long period. Results highlighted distinctive spatiotemporal patterns of microbial communities in water columns mainly driven by sulfate, dissolved oxygen, nitrate and temperature, whilst sediment communities only showed a seasonal variation pattern governed by pH, reduced inorganic sulfur, sulfate, organic matter and total nitrogen. Microbial co-occurrence networks revealed the succession of keystone taxa in both water columns and sediments, reflecting core ecological functions in response to altered environmental conditions. Specifically, in shallow water, keystone nitrogen fixers and denitrifiers were responsible for providing nitrogen nutrients in summer, while recalcitrant substance degraders likely supplied microbially available organic matters to maintain ecosystem stability in winter. But in deep water, methane oxidation was the critical process linked to microbial-mediated cycle of carbon, nitrogen and sulfur. In addition, carbon metabolism and mercury methylation mediated by sulfate reducers, denitrifiers and nitrogen fixers were core functioning features of sediments in summer and winter, respectively. This work expands our knowledge of the importance of keystone taxa in maintaining stability of reservoir ecosystems under changing environments, providing new perspectives for water resource conservation and management.

Multi-Soil-Layering Technology: A New Approach to Remove Microcystis aeruginosa and Microcystins from Water

Eutrophication of surface waters caused by toxic cyanobacteria such as Microcystis aeruginosa leads to the release of secondary metabolites called Microcystins (MCs), which are heptapeptides with adverse effects on soil microbiota, plants, animals, and human health. Therefore, to avoid succumbing to the negative effects of these cyanotoxins, various remediation approaches have been considered. These techniques involve expensive physico-chemical processes because of the specialized equipment and facilities required. Thus, implementing eco-technologies capable of handling this problem has become necessary. Indeed, multi-soil-layering (MSL) technology can essentially meet this requirement. This system requires little space, needs simple maintenance, and has energy-free operation and high durability (20 years). The performance of the system is such that it can remove 1.16 to 4.47 log10 units of fecal contamination from the water, 98% of suspended solids (SS), 92% of biological oxygen demand (BOD), 98% of chemical oxygen demand (COD), 92% of total nitrogen (TN), and 100% of total phosphorus (TP). The only reported use of the system to remove cyanotoxins has shown a 99% removal rate of MC-LR. However, the mechanisms involved in removing this toxin from the water are not fully understood. This paper proposes reviewing the principal methods employed in conventional water treatment and other technologies to eliminate MCs from the water. We also describe the principles of operation of MSL systems and compare the performance of this technology with others, highlighting some advantages of this technology in removing MCs. Overall, the combination of multiple processes (physico-chemical and biological) makes MSL technology a good choice of cyanobacterial contamination treatment system that is applicable in real-life conditions, especially in rural areas.

Effect of overlying water pH, temperature, and hydraulic disturbance on heavy metal and nutrient release from drinking water reservoir sediments

How environmental factors impact the release of pollutants from sediment is critical to ensure the safety of drinking water, especially when the seasons change. Here, we investigated the effect of water pH, temperature, and hydraulic disturbance on the release of heavy metals and nutrients from the sediment of drinking water reservoir. The results show that lower initial water pH promoted the Zn release, while low temperature enhanced the Mn flux after 15 days. Meanwhile, continuous disturbance caused more metals releasing from sediment than intermittent disturbance due to greater shear stress and turbulence effect. However, intermittent high-speed disturbance greatly altered the dynamic release of Zn from L-shaped curve to U-shape in water column. Moreover, lower water pH caused higher ammonium in water but lower nitrate since H⁺ restrained the nitrification. Yet, higher temperature inhibited the release of ammonium from sediment, which might relate to the accelerated mineralization of organic nitrogen and elevated dissolved oxygen caused by the algae growth. Notably, hydraulic disturbance with various intensity and duration greatly influenced the fluxes of various species of nitrogen and soluble phosphate in water column, because the disturbance facilitated the nitrogen and phosphorus exchanges between sediment-water and water-air interfaces. PRACTITIONER POINTS: Lower water pH induced Zn release, while low temperature gradually enhanced Mn level. More metals were released from sediment under continuous disturbance than intermittent disturbance. Lower water pH caused higher ammonium nitrogen in water but lower nitrate nitrogen. Higher temperature inhibited the release of ammonium nitrogen from sediment. Hydraulic disturbance greatly changed the release of different species of nitrogen and soluble phosphate from sediment.

Analysis of Antibiotic Resistance Genes, Environmental Factors, and Microbial Community From Aquaculture Farms in Five Provinces, China

The excessive use of antibiotics speeds up the dissemination and aggregation of antibiotic resistance genes (ARGs) in the environment. The ARGs have been regarded as a contaminant of serious environmental threats on a global scale. The constant increase in aquaculture production has led to extensive use of antibiotics as a means to prevent and treat bacterial infections; there is a universal concern about the environmental risk of ARGs in the aquaculture environment. In this study, a survey was conducted to evaluate the abundance and distributions of 10 ARGs, bacterial community, and environmental factors in sediment samples from aquatic farms distributed in Anhui (AP1, AP2, and AP3), Fujian (FP1, FP2, and FP3), Guangxi (GP1, GP2, and GP3), Hainan (HP1, HP2, and HP3), and Shaanxi (SP1, SP2, and SP3) Province in China. The results showed that the relative abundance of total ARGs was higher in AP1, AP2, AP3, FP3, GP3, HP1, HP2, and HP3 than that in FP1, FP2, GP1, GP2, SP1, SP2, and SP3. The sul1 and tetW genes of all sediment samples had the highest abundance. The class 1 integron (intl1) was detected in all samples, and the result of Pearson correlation analysis showed that the intl1 has a positive correlation with the sul1, sul2, sul3, bla_OXA, qnrS, tetM, tetQ, and tetW genes. Correlation analysis of the bacterial community diversity and environmental factors showed that the Ca²⁺ concentration has a negative correlation with richness and diversity of the bacterial community in these samples. Of the identified bacterial community, Proteobacteria, Firmicutes, Chloroflexi, and Bacteroidota were the predominant phyla in these samples. Redundancy analysis showed that environmental factors (TN, TP, Cl^–, and Ca²⁺) have a positive correlation with the bacterial community (AP1, GP1, GP2, GP3, SP1, SP2, and SP3), and the abundance of ARGs (sul1, tetW, qnrS, and intl1) has a positive correlation with the bacterial community (AP2, AP3, HP1, HP2, and HP3). Based on the network analysis, the ARGs (sul1, sul2, bla_CMY, bla_OXA, qnrS, tetW, tetQ, tetM, and intl1) were found to co-occur with bacterial taxa from the phyla Chloroflexi, Euryarchaeota, Firmicutes, Halobacterota, and Proteobacteria. In conclusion, this study provides an important reference for understanding the environmental risk associated with aquaculture activities in China.

Picophytoplankton identification by flow cytometry and high-throughput sequencing in a clean reservoir

Understanding picophytoplankton variations that play important roles in the material circulation and energy flow are critical to assessing overall status of waterbody, especially for clean reservoirs which remain a relatively stable community structure and high species diversity due to lower nitrogen and phosphorus nutrients. However, their response to key environmental factors and tightly acting microbial remains poorly understood. Traditional quantification methods are limited, such as chlorophyll-a, turbidity and microscope. There are still many defects with present molecular analysis. In this study, a flow cytometric analysis and high-throughput sequencing combination methodology was developed and tested on clean water from a reservoir, by a monthly dynamic for a vegetative period April-September in 2019 to improve the accuracy of dynamic monitoring for the picophytoplankton system. More species of Pico-Cyanobacteria and Pico-Eukaryotes were discovered. The increased percentage of pigment compounds from 8.2% to 76.3% proves the effective reduce of heterotrophic disturbing and enrichment of target populations. Picophytoplankton that was previously neglected due to their low relative abundance has once again entered the scope of our eyes. Phytoplankton were divided into three categories. The first one was the highly abundant and frequently present taxa, the second one was the low-abundance but highly-transient population, and the third one was the low abundance and stable group. Synechococcus, Emiliania, Tetraselmis and Thalassiosira were dominant picophytoplankton and displayed obvious temporal and spatial distribution characteristics. Pico-PE rich Cyanobacteria and Nano-Eukaryotes with high transience abnormally increased in summer. Temperature, ammonia-N, nitrate-N, turbidity and total nitrogen were most influencing factors, while some picophytoplankton with special physiological structure showed distinct competitive advantages in the microbial community. As for the off-flavor compounds, the concentration of 2-methylisoborneol and geosmin were high even 66.7% and 20.8% of the samples exceeded their olfactory threshold. Chrysochromuina, Planktothrix and Microcystis might be the potential producers.

Release of odorants from sediments of the largest drinking water reservoir in Shanghai: Influence of pH, temperature, and hydraulic disturbance

Endogenous pollution from sediments is gradually becoming a critical pollution source of the drinking water reservoir. Odorants can be released from sediments into the overlying water which further deteriorate the water quality of the drinking water reservoir. In this work, we set the sediment-overlying water systems under various water pH (6.5, 8 and 9), temperature (4, 20 and 30 °C) during 30 days and intermittent or continuous hydraulic disturbances (at 100 r/min or 200 r/min) in 5 days, and investigated the dynamic release of odorants from the drinking water reservoir sediments via using headspace solid-phase microextraction (HSPME) and gas chromatography-mass spectrometry (GC-MS). The result shows that weakly alkaline environment slightly but not significantly increased the concentration of dimethyl disulfide (DMDS) in the overlying water. Furthermore, low temperature promoted the release of bis(2-chloroisopropyl) ether (BCIE) and geosmin to 108.36 and 18.98 ng/L, respectively, while high temperature facilitated the DMDS release to 20.33 ng/L. Notably, hydraulic disturbances drastically elevated the level of seven odorants released from the sediments. Specially, benzaldehyde exhibited highest concentration at 260.50 ng/L. The continuous disturbance greatly enhanced the release of benzaldehyde, DMDS, dimethyl trisulfide (DMTS), BCIE and 1,4-dichloro-benzene (1,4-DCB) from sediments with a positive disturbance speed-dependence. However, the intermittent disturbance promoted higher level of geosmin in the overlying water compared to the continuous disturbance. Only continuous hydraulic disturbance at high speed could lead to the release of ethylbenzene from sediments, which was up to 4.89 ng/L in 12 h.

The involvement of α-proteobacteria Phenylobacterium in maintaining the dominance of toxic Microcystis blooms in Lake Taihu, China

Lake Taihu in China has suffered serious harmful cyanobacterial blooms for decades. The algal blooms threaten the ecological sustainability, drinking water safety, and human health. Although the roles of abiotic factors (such as water temperature and nutrient loading) in promoting Microcystis blooms have been well studied, the importance of biotic factors (e.g. bacterial community) in promoting and meditating Microcystis blooms remains unclear. In this study, we investigated the ecological dynamics of bacterial community, the ratio of toxic Microcystis, as well as microcystin in Lake Taihu. High-throughput 16S rRNA sequencing and principal component analysis (PCA) revealed that the bacteria community compositions (BCCs) clustered into three groups, the partitioning of which corresponded to that of groups according to the toxic profiles (the ratio of toxic Microcystis to total Microcystis, and the microcystin concentrations) of the samples. Further Spearman's correlation network showed that the α-proteobacteria Phenylobacterium strongly positively correlated with the toxic profiles. Subsequent laboratory chemostats experiments demonstrated that three Phenylobacterium strains promoted the dominance of the toxic Microcystis aeruginosa PCC7806 when co-culturing with the non-toxic PCC7806 mcyB^- mutant. Taken together, our data suggested that the α-proteobacteria Phenylobacterium may play a vital role in the maintenance of toxic Microcystis dominance in Lake Taihu.

Disentangling the drivers of Microcystis decomposition: Metabolic profile and co-occurrence of bacterial community

In aquatic ecosystems, water microbial communities can trigger the outbreak or decline of cyanobacterial blooms. However, the microbiological drivers of Microcystis decomposition in reservoirs remain unclear. Here, we explored the bacterial community metabolic profile and co-occurrence dynamics during Microcystis decomposition. The results showed that the decomposition of Microcystis greatly altered the metabolic characteristics and composition of the water bacterial community. Significant variations in bacterial community composition were observed: the bacterial community was mainly dominated by Proteobacteria, Actinobacteria, Planctomycetes, and Bacteroidetes during Microcystis decomposition. Additionally, members of Exiguobacterium, Rhodobacter, and Stenotrophomonas significantly increased during the terminal stages. Dissolved organic matters (DOM) primarily composed of fulvic-like, humic acid-like, and tryptophan-like components, which varied distinctly during Microcystis decomposition. Additionally, the metabolic activity of the bacterial community showed a continuous decrease during Microcystis decomposition. Functional prediction showed a sharp increase in the cell communication and sensory systems of the bacterial communities from day 12 to day 22. Co-occurrence networks showed that bacteria responded significantly to variations in the dynamics of Microcystis decomposition through close interactions between each other. Redundancy analysis (RDA) indicated that Chlorophyll a, nitrate nitrogen (NO₃^--N), dissolved oxygen (DO), and dissolved organic carbon (DOC) were crucial drivers for shaping the bacterial community structure. Taken together, these findings highlight the dynamics of the water bacterial community during Microcystis decomposition from the perspective of metabolism and community composition, however, further studies are needed to understand the algal degradation process associated with bacteria.

Seasonal dynamics of lotic bacterial communities assessed by 16S rRNA gene amplicon deep sequencing

Aquatic microbial diversity, composition, and dynamics play vital roles in sustaining water ecosystem functionality. Yet, there is still limited knowledge on bacterial seasonal dynamics in lotic environments. This study explores a temporal pattern of bacterial community structures in lotic freshwater over a 2-year period. The aquatic bacterial communities were assessed using Illumina MiSeq sequencing of 16S rRNA genes. Overall, the communities were dominated by α-, β-, and γ-Proteobacteria, Bacteroidetes, Flavobacteriia, and Sphingobacteriia. The bacterial compositions varied substantially in response to seasonal changes (cold vs. warm), but they were rather stable within the same season. Furthermore, higher diversity was observed in cold seasons compared to warm periods. The combined seasonal-environmental impact of different physico-chemical parameters was assessed statistically, and temperature, suspended solids, and nitrogen were determined to be the primary abiotic factors shaping the temporal bacterial assemblages. This study enriches particular knowledge on the seasonal succession of the lotic freshwater bacteria.

Comparison of the groundwater microbial community in a salt-freshwater mixing zone during the dry and wet seasons

To gain a better understanding of the microbial community in salt-freshwater mixing zones, in this study, the influence of seasonal variation on the groundwater microbial community was evaluated by high throughput 16S rDNA gene sequencing. The results showed that notable changes in microbial community occurred in a salt-freshwater mixing zone and the groundwater samples in the dry season were more saline than those in the wet season. The increase in precipitation during the wet season relieved local seawater intrusion. Microbial diversity varied greatly with seasons, while no obvious change pattern was found. Proteobacteria was identified as the dominant phylum in all samples. The genus Hydrogenophaga dominated in the dry season, while the genus Acidovorax dominated in the wet season. Dissolved oxygen affected the diversity of the microbial communities during the dry and wet season, while groundwater level had a strong influence on the structure of microbial communities. Phylogenetic molecular network analysis of the microbial communities indicated that increased seawater intrusion led to a more compact microbial network and strengthening the groundwater microbial interactions.

Planktonic Bacterial and Archaeal Communities in an Artificially Irrigated Estuarine Wetland: Diversity, Distribution, and Responses to Environmental Parameters

Bacterial and archaeal communities play important roles in wetland ecosystems. Although the microbial communities in the soils and sediments of wetlands have been studied extensively, the comprehensive distributions of planktonic bacterial and archaeal communities and their responses to environmental variables in wetlands remain poorly understood. The present study investigated the spatiotemporal characteristics of the bacterial and archaeal communities in the water of an artificially irrigated estuarine wetland of the Liaohe River, China, explored whether the wetland effluent changed the bacterial and archaeal communities in the Liaohe River, and evaluated the driving environmental factors. Within the study, 16S rRNA quantitative PCR methods and MiSeq high-throughput sequencing were used. The bacterial and archaeal 16S rRNA gene abundances showed significant temporal variation. Meanwhile, the bacterial and archaeal structures showed temporal but not spatial variation in the wetland and did not change in the Liaohe River after wetland drainage. Moreover, the bacterial communities tended to have higher diversity in the wetland water in summer and in the scarce zone, while a relatively higher diversity of archaeal communities was found in autumn and in the intensive zone. DO, pH and PO₄-P were proven to be the essential environmental parameters shaping the planktonic bacterial and archaeal community structures in the Liaohe River estuarine wetland (LEW). The LEW had a high potential for methanogenesis, which could be reflected by the composition of the microbial communities.

Homogeneous selection dominates the microbial community assembly in the sediment of the Three Gorges Reservoir

Deep-water reservoir sediment is a unique habitat sheltering indispensable microorganisms and facilitating their biogeochemical functions; however, the assembly processes of the microbial community therein remain elusive. This study focuses on the assembly processes in the Three Gorges Reservoir Area (TGRA). A total of 42 sediment samples were collected from the TGRA, both in the mainstream and the tributaries, and in different seasons. Metagenomic analyses of 16S rRNA using Exact Sequence Variants revealed the spatiotemporal distribution patterns of the microbial communities. Linear regressions between dissimilarity of microbial communities, geographic and environmental distance showed that environmental, rather than geographic factors, impacted the microbial community. However, the environmental differences explained little variations (14.14%) in community structure, implying the homogeneity of environmental conditions across the TGRA. From the quantification of ecological processes, homogeneous selection was shown to be a dominating factor (51.34%) in the assembly of the microbial communities. The co-occurrence network showed that keystone species were more important than prevalent abundant species in interspecies interactions. Overall, the assembly of microbial community in the deep-water reservoir sediment is mediated by both deterministic and stochastic processes, and homogeneous selection plays a leading role.

Field Research on Mixing Aeration in a Drinking Water Reservoir: Performance and Microbial Community Structure

Field research on the performance of pollutant removal and the structure of the microbial community was carried out on a drinking water reservoir. After one month of operation of a water-lifting aeration system, the water temperature difference between the bottom and the surface decreased from 9.9 to 3.1 °C, and the concentration of the dissolved oxygen (DO) in the bottom layer increased from 0 to 4.2 mg/L. The existing stratification in the reservoir was successfully eliminated. Total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) concentrations were reduced by 47.8%, 66.7%, and 22.9%, respectively. High-throughput sequencing showed that Proteobacteria, Bacteroides, and Actinomycetes accounted for 67.52% to 78.74% of the total bacterial population. Differences in the bacterial changes were observed between the enhanced area and the control area. With the operation of the water-lifting aeration system, the populations of bacteria of the main genera varied temporally and spatially. Principal component analysis pointed out a clear evolution in the vertical distribution of the microbial structure controlled by the operation of the aeration system. Permutational analysis of variance showed a significant difference in the microbial community (p < 0.01). Redundancy analysis showed that physical (water temperature, DO) and chemical environmental factors (Chl-a, TOC, TN) were the key factors affecting the changes in the microbial communities in the reservoir water. In addition, a hierarchical partitioning analysis indicated that T, Chl-a, ORP, TOC, pH, and DO accounted for 24.1%, 8.7%, 6.7%, 6.2%, 5.8%, and 5.1% of such changes, respectively. These results are consistent with the ABT (aggregated boosted tree) analysis for the variations in the functional bacterial community, and provide a theoretical basis for the development and application of biotechnology.

Seasonality overwhelms aquacultural activity in determining the composition and assembly of the bacterial community in Lake Taihu, China

Aquaculture accounts for an extremely valuable and rapidly expanding sector of global food production, yet its environmental impacts on aquatic ecosystems have attracted much concern. In this study, we collected water samples from eastern Lake Taihu, China. We targeted sites varying in their intensity of aquacultural activities and sampled them over multiple seasons. For each sample, we measured physicochemical variables, and we sequenced the 16S rRNA gene of the respective bacterial communities using an Illumina second-generation sequencing platform. Marked differences in diversity and bacterial community composition were observed between seasons, whereas we observed relatively weak differences between sites. Remarkable differences in the abundance of the bacterial community were observed at the phylum and genus levels across the different seasons. Stochastic processes dominated the assembly of bacterial communities in the aquaculture-influenced systems, and the assembly processes of bacterial community differed between seasons. Our observations highlight the effect of seasonality on bacterial communities and provide a more complete knowledge base for the proper assessment of the effects of aquacultural activities on freshwater ecosystems.

The Characteristics and Dynamics of Cyanobacteria-Heterotrophic Bacteria Between Two Estuarine Reservoirs - Tropical Versus Sub-Tropical Regions

In this study, Illumina MiSeq sequencing technique was employed to explore the characteristics and dynamics of cyanobacteria–heterotrophic bacteria between two estuarine reservoirs in sub-tropical (reservoir A in Shanghai) and tropical (reservoir B in Singapore) regions. The results indicated that significant differences in bacterial community composition were found between two estuarine reservoirs, which influenced by varied environmental variables. The environmental heterogeneity in reservoir A was much higher, which indicated that the composition of bacterial community in reservoir A was more complex. In contrast, reservoir B provided a suitable and temperate water environment conditions for bacterial growth, which resulted in higher community diversity and less co-exclusion correlations. The molecular ecological network indicated that the presence of dominant bacterial community in each of the reservoir were significant different. These differences mainly reflected the responses of bacterial community to the variations of environmental variables. Although Synechococcus was the dominant cyanobacterial species in both reservoirs, it exhibited co-occurrence patterns with different heterotrophic bacteria between reservoirs. In addition, the cyanobacteria–heterotrophic bacteria interaction exhibited highly dynamic variations, which was affected by nutrition and survive space. Also, the co-occurrence of Microcystis and Pseudanabaena found in reservoir B implied that the non-N-fixing Microcystis accompanied with N-fixing Pseudanabeana occurrence in freshwater lakes, so as to better meet the demand for nitrogen source.

Variations of Bacterial Community Composition and Functions in an Estuary Reservoir during Spring and Summer Alternation

In this study, we focused on the dynamics of bacterial community composition in a large reservoir in the Yangtze estuary during spring and summer seasons, especially the variations of functional mechanisms of microbial community during the seasonal alternation between spring and summer. Both 16S rRNA gene sequencing and shotgun metagenomic sequencing technology were used for these purposes. The results indicated that obvious variations of bacterial community structures were found at different sites. Particle-associated bacterial taxa exhibited higher abundance at the inlet site, which was closer to the Yangtze River with a high level of turbidity. In other sites, Synechococcus, as the most dominant cyanobacterial species, revealed high abundance driven by increased temperature. Moreover, some heterotrophic bacterial taxa revealed high abundance following the increased Synechococcus in summer, which indicated potential correlations about carbon source utilization between these microorganisms. In addition, the shotgun metagenomic data indicated during the period of seasonal alternation between spring and summer, the carbohydrate transport and metabolism, energy production and conversion, translation/ribosomal biogenesis, and cell wall/membrane/envelope biogenesis were significantly enhanced at the exit site. However, the course of cell cycle control/division was more active at the internal site.