Epiphytic bacterial community shift drives the nutrient cycle during Potamogeton malaianus decomposition

Decomposition of exotic versus native aquatic plant litter in a lake littoral zone: Stoichiometry and life form analyses

The decomposition rates and stoichiometric characteristics of many aquatic plants remain unclear, and our understanding of material flow and nutrient cycles within freshwater ecosystems is limited. In this study, an in-situ experiment involving 23 aquatic plants (16 native and 7 exotic species) was carried out via the litter bag method for 63 days, during which time the mass loss and nutrient content (carbon (C), nitrogen (N), and phosphorus (P)) of plants were measured. Floating-leaved plants exhibited the highest decomposition rate (0.038 ± 0.002 day-1), followed by submerged plants and free-floating plants (0.029 ± 0.002 day-1), and emergent plants had the lowest decomposition rate (0.019 ± 0.001 day-1). Mass loss by aquatic plants correlated with stoichiometric characteristics; the decomposition rate increased with an increasing P content and with a decreasing C content, C:N ratio, and C:P ratio. Notably, the decomposition rate of submerged exotic plants (0.044 ± 0.002 day-1) significantly exceeded that of native plants (0.026 ± 0.004 day-1), while the decomposition rate of emergent exotic plants was 55 ± 4 % higher than that of native plants. The decomposition rates of floating-leaved and free-floating plants did not significantly differ between the native and exotic species. During decomposition, emergent plants displayed an increase in C content and a decrease in N content, contrary to patterns observed in other life forms. The P content decreased for submerged (128 ± 7 %), emergent (90 ± 5 %), floating-leaved (104 ± 6 %), and free-floating plants (32 ± 6 %). Exotic plants released more C and P but accumulated more N than did native plants. In conclusion, the decomposition of aquatic plants is closely linked to litter quality and influences nutrient cycling in freshwater ecosystems. Given these findings, the invasion of the littoral zone by submerged and emergent exotic plants deserves further attention.

Submerged macrophyte promoted nitrogen removal function of biofilms in constructed wetland

Biofilm is one of the important factors affecting nitrogen removal in constructed wetlands (CWs). However, the impact of submerged macrophyte on nitrogen conversion of biofilms on leaf of submerged macrophyte and matrix remains poorly understood. In this study, the CWs with Vallisneria natans and with artificial plant were established to investigate the effects of submerged macrophyte on nitrogen conversion and the composition of nitrogen-converting bacteria in leaf and matrix biofilms under high ammonium nitrogen (NH4+-N) loading. The 16S rRNA sequencing method was employed to explore the changes in bacterial communities in biofilms in CWs. The results showed that average removal rates of total nitrogen and NH4+-N in CW with V. natans reached 71.38% and 82.08%, respectively, representing increases of 24.19% and 28.79% compared with the control with artificial plant. Scanning electron microscope images indicated that high NH4+-N damaged the leaf cells of V. natans, leading to the cellular content release and subsequent increases of aqueous total organic carbon. However, the specific surface area and carrier function of V. natans were unaffected within 25 days. As a natural source of organic matters, submerged macrophyte provided organic matters for bacterial growth in biofilms. Bacterial composition analysis revealed the predominance of phylum Proteobacteria in CW with V. natans. The numbers of nitrifiers and denitrifiers in leaf biofilms reached 1.66 × 105 cells/g and 1.05 × 107 cells/g, as well as 2.79 × 105 cells/g and 7.41 × 107 cells/g in matrix biofilms, respectively. Submerged macrophyte significantly increased the population of nitrogen-converting bacteria and enhanced the expressions of nitrification genes (amoA and hao) and denitrification genes (napA, nirS and nosZ) in both leaf and matrix biofilms. Therefore, our study emphasized the influence of submerged macrophyte on biofilm functions and provided a scientific basis for nitrogen removal of biofilms in CWs.

Ecological role of reed belts in lakeside zone: Impacts on nutrient retention and bacterial community assembly during Hydrilla verticillata decomposition

Reed belts acting as basic nutrient filters are important parts of lake buffer riparian zones. However, little is known about their impacts on nutrient release and bacterial community during plant litter decomposition. In this study, a field experiment was conducted in west-lake Taihu to monitor the changes in nutrients, bacterial enzymatic activities, and bacterial community in plant debris during Hydrilla verticillata (H. verticillata) decomposition in open water (HvC) and reed belts (HvL) area for 126 days. We found that there was lower temperature but higher nutrient concentrations in overlying water in HvL than HvC. Partial least squares path modeling revealed that environmental parameters in overlying water had important impacts on bacterial activities and nutrient release (such as alkaline phosphatase, cellulase, and soluble sugar) and therefore affected dissolved organic matter components in plant debris. According to Illumina sequencing, 46,003 OTUs from 10 dominant phyla were obtained and Shannon index was higher in HvL than HvC at the same sampling time. Neutral community model explained 49% of bacterial community variance and immigration rate by the estimate of dispersal in HvC (Nm: 27,154) and HvL (Nm: 25,765), respectively. Null model showed stochastic factors governed the bacterial community assembly in HvC (66.67%) and HvL (87.28%). TP and pH were key factors affecting the bacterial community structure at the phylum level. More hubs and complex interactions among bacteria were observed in HvL than HvC. Function analysis showed bacterial community had important role in carbon, organic phosphorus, and nitrogen removal but phosphorus-starvation was detected in debris of H. verticillata. This study provides useful information for understanding the changes in nutrients and bacterial community in litter during H. verticillata decomposition and highlights the role of reed belts on retained plant litter to protect lake from pollution.

Elucidating potential bioindicators from insights in the diversity and assembly processes of prokaryotic and eukaryotic communities in the Mekong River

Drivers for spatio-temporal distribution patterns of overall planktonic prokaryotes and eukaryotes in riverine ecosystems are generally not fully understood. This study employed amplicon metabarcoding to investigate the distributions and assembly mechanisms of bacterial and eukaryotic communities in the Mekong River. The prevailing bacteria taxa were found to be Betaproteobacteria, Actinobacteria, and Bacteroidetes, while the dominant eukaryotic organisms were cryptophytes, chlorophytes, and diatoms. The community assemblages were influenced by a combination of stochastic and deterministic processes. Drift (DR) and dispersal limitation (DL), signifying the stochastic mechanism, were the main processes shaping the overall prokaryotic and eukaryotic communities. However, homogeneous selection (HoS), indicating deterministic mechanism, played a major role in the assembly process of core prokaryotic communities, especially in the wet season. In contrast, the core eukaryotic communities including Opisthokonta, Sar, and Chlorophyta were dominated by stochastic processes. The significance of HoS within prokaryotic communities was also found to exhibit a decreasing trend from the upstream sampling sites (Chiang Saen and Chiang Khan, Nong Khai) towards the downstream sites (Mukdahan, and Khong Chiam) of the Mekong River. The environmental gradients resulting from the site-specific variations and the gradual decrease in elevation along the river may have a potential influence on the role of HoS in community assembly. Crucial environmental factors that shape the phylogenetic structure within distinct bins of the core prokaryotic communities including water depth, temperature, chloride, sodium, and sulphate were identified, as inferred by their correlation with the beta Net Relatedness Index (betaNRI) during the wet season. Overall, these findings enhance understanding of the complex mechanisms governing the spatio-temporal dynamics of prokaryotic and eukaryotic communities in the Mekong River. Finally, insights gained from this study could provide information on further use of specific core bacteria as microbial-based bioindicators that are effective for the assessment and conservation of the Mekong River ecosystem.

Microbial-driven carbon fixation in natural wetland

With the development of global industrialization, carbon neutrality has become an issue that we must be paid attention to. Microorganisms not only have an important impact on the carbon chemical cycle between the Earth's biosphere and biogeography but also play a key role in maintaining the global organic carbon balance. Wetlands are the main reservoir of organic carbon in the mainland of China, and wetland carbon sinks are indispensable for China to achieve the goal of "dual carbon," and China has taken the consolidation and improvement of wetland carbon sink capacity as an important part of the carbon peaking action plan. As a unique low-latitude, high-altitude seasonal plateau wetland in China, Napahai shows high research value. However, the role of microbes in maintaining dissolved organic carbon balance in this area has not been reported. In the study, six carbon fixation genes, accA, aclB, acsA, acsB, cbbL, and rbcL, were analyzed based on metagenomics to elucidate the rich genetic diversity, uniqueness and differences in the Napahai plateau wetland. It was found that the microbial diversity in the Napahai plateau wetland was different from other habitats. In addition, the aclB gene, a rare taxon with high genetic diversity and rich species in the Napahai plateau wetland, played a key role in the microbial metabolic pathway. Finally, the construction of a metabolic pathway through the Kyoto encyclopedia for genes and genomes revealed the contribution of microbes to carbon fixation and the role of microbes in maintaining the organic carbon balance of the Napahai plateau wetland.

Vegetated urban streams have sufficient purification ability but high internal nutrient loadings: Microbial communities and nutrient release dynamics

The release of nutrients back into the water column due to macrophyte litter decay could offset the benefits of nutrient removal by hydrophytes within urban streams. However, the influence of this internal nutrient cycling on the overlying water quality and bacterial community structure is still an open question. Hence, litter decomposition trials using six hydrophytes, Typha latifolia (TL), Phragmites australis (PAU), Hydrilla verticillata (HV), Oenanthe javanica (OJ), Myriophyllum aquaticum (MA), and Potamogeton crispus (PC), were performed using the litterbag approach to mimic a 150-day plant litter decay in sediment-water systems. Field assessment using simple in/out mass balances and uptake by plant species was carried out to show the potential for phytoremediation and its mechanisms. Results from two years of monitoring (2020-2021) indicated mean total nitrogen (TN) retention efficiencies of 7.2-60.14 % and 9.5-55.6 % for total phosphorus (TP) in the studied vegetated urban streams. Nutrient retention efficiencies showed temporal variations, which depended on seasonal temperature. Mass balance analysis indicated that macrophyte assimilation, sediment adsorption, and microbial transformation accounted for 10.31-41.74 %, 0.84-3.00 %, and 6.92-48.24 % removal of the inlet TN loading, respectively. Hydrophyte detritus decay induced alterations in physicochemical parameters while significantly increasing the N and P levels in the overlying water and sediment. Decay rates varied among macrophytes in the order of HV (0.00436 g day^-1) > MA (0.00284 g day^-1) > PC (0.00251 g day^-1) > OJ (0.00135 g day^-1) > TL (0.00095 g day^-1) > PAU (0.00057 g day^-1). 16S rRNA gene sequencing analysis showed an increase in microbial species richness and diversity in the early phase of litter decay. The abundances of denitrification (nirS and nirK) and nitrification (AOA and AOB) genes also increased in the early stage and then decreased during the decay process. Results of this study conducted in seven urban streams in northern China demonstrate the direct effects of hydrophytes in encouraging nutrient transformation and stream self-purification. Results also demonstrate that macrophyte detritus decay could drive not only the nutrient conversions but also the microbial community structure and activities in sediment-water systems. Consequently, to manage internal sources and conversions of nutrients, hydrophytic detritus (e.g., floating/submerged macrophytes) must be suppressed and harvested.

Regulation of the Nutrient Cycle Pathway and the Microbial Loop Structure by Different Types of Dissolved Organic Matter Decomposition in Lakes

To explore the effect of different types of dissolved organic matter (DOM) decomposition on nutrient cycling pathways and the microbial loop, four lakes with different DOM sources were investigated monthly. In Lake Tangxun, Dolichospermum decay released highly labile dissolved organic nitrogen into the water column. This induced bacterial organic nitrogen decomposition, as indicated by the increased abundance of gltB, gltD, gdh, and glnA as well as aminopeptidase activity. Genes associated with dissimilatory nitrate reduction to ammonium further fueled ammonium accumulation, driving Microcystis blooms in the summer. In Lake Zhiyin, fish bait deposits (high nitrogen, similar to Dolichospermum detritus) also caused Microcystis blooms. Detritus from Microcystis decomposition then produced high levels of labile dissolved organic phosphorus, inducing phosphatase activity and increasing soluble reactive phosphorus concentrations from September to April in Lakes Tangxun and Zhiyin. The high refractory DOM from macrophytes in Lake Houguan led to insufficient nutrient availability, leading to nutrient mutualism between algae and bacteria. The high levels of labile dissolved organic carbon from terrestrial detritus in Lake Yandong increased bacterial biomass and production, resulting in low chlorophyll content due to the competitive relationship between algal and bacterial nutrient requirements. Therefore, different DOM compositions induce unique connections among available nutrients, algae, and bacteria in the microbial loop.

Linking fluorescent dissolved organic matters to microbial carbon metabolism in the overlying water during submerged macrophyte Potamogeton crispus L decomposition in the presence/absence of Vallisneria natans

Multi-species submerged plants grow with succession patterns in the same habit and play an important role in the aquatic ecosystems. The decomposition of submerged plants in aquatic environments was a disturbance that affected the water quality and microbial community structures. However, the responses of the microbial community function in surface water to the disturbance remain poorly understood. In this study, the effects of submerged macrophyte Potamogeton crispus L decomposition on the water quality and microbial carbon metabolism functions (MCMF) in the overlying water were investigated in the presence/absence of Vallisneria natans. The result showed that the decomposition rapidly released a large amount of organic matter and nutrients into the overlying water. The presence of Vallisneria natans promoted the removal of dissolved organic carbon and fluorescent component C3, resulting in lower values of the percentage content of C3 (C3%). Under various decomposition processes, the MCMF changed over time and significantly negatively correlated with C3%. The functional diversity of MCMF significantly correlated with the fluorescence organic matters, such as the richness and Simpson index correlated with the amount of C1, C1+C2+C3, and C3%. But UV-visible absorption indexes and nutrients in the overlying water had no relationship with the MCMF, except for the total nitrogen correlated with the richness. These results suggested that under various decomposition conditions, the fluorescent dissolved organic matter could be used as an indicator for quick prediction of MCMF in surface water.

Metagenomic Analysis Reveals the Response of Microbial Communities and Their Functions in Lake Sediment to Environmental Factors

Jingpo Lake is the largest mountain barrier lake in China and plays a key role in breeding, power generation, and providing a source of drinking water. Microbes are important participants in the formation of lake resources and energy cycles. However, the ecological protection of Jingpo Lake has faced serious challenges in recent years. In this study, we investigate the responses of the microbial community's composition of sediments at five locations to an environmental gradient representing water quality and water-depth changes using a metagenomic sequence. We found that the diversity and composition of the microbiota sediments were altered spatially and correlated with the physicochemical factors of water samples. In the microbial community, relatively lower Chao1, alternating conditional expectations, and Shannon and Simpson indices were found at the shallowest location with higher total phosphorus and chlorophyll a. Furthermore, the Kyoto Encyclopedia of Genes and Genomes analysis revealed that the metabolism function was the most abundant functional classification in Jingpo Lake. The levels of total phosphorus, chlorophyll a and pH were positively correlated with the abundance of Flavobacterium and the bacterial functions of the carbohydrate metabolism and amino acid metabolism. In conclusion, our results reveal the physical and chemical characteristics, as well as the microbial community characteristics, of Jingpo Lake, which provides new insights for studying the relationship between environmental factors and the bacterial community distribution of freshwater ecosystems, in addition to also providing a theoretical basis for the environmental monitoring and protection of the lake.

Trace metal complexation with dissolved organic matter stresses microbial metabolisms and triggers community shifts: The intercorrelations

The response of microorganisms to heavy metal-dissolved organic matter (Me-DOM) complexation is critical for the microbial-mediated coupled biogeochemical cycling of metals and DOM. This study investigated the impact of typical metals [As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn (at an environmentally-relevant concentration of 200 ppb)], model DOM substrates [humic acids (HA) and bovine serum albumin (BSA)], and their complexation on riverine microbial DOM metabolisms. DOM biodegradability decreased after the metal complexation (especially Co, Cr, and Mn for HA and Ni for BSA). While microbial transformation of humics and proteins was observed, components with lower aromaticity and hydrophobicity were accumulated during the cultivation. The substrate difference and metal speciation changed community compositions and resulted in distinctive community member networks, which accounted for the varied metabolic DOM patterns. The correlations indicated that rather than metal uptakes, Me-DOM complexation and community shifts controlled microbial DOM metabolisms. Microbial BSA metabolisms were less correlated to the key genera identified by network analysis or community diversity. Instead, they were sensitive to metal speciation, which may be attributed to the complicated utilization and production of proteins and their essential roles in detoxification. The constructed correlations among metals (Me-DOM complexes), DOM metabolisms, and community shifts provide strong implications for the biogeochemical function of Me-DOM complexes and highlight the effect of metal speciation on microbial protein metabolisms even at trace concentrations.

Comparison of epiphytic and intestinal bacterial communities in freshwater snails (Bellamya aeruginosa) living on submerged plants

The combination of submerged plants and snails can combat eutrophication of freshwater systems by suppressing algal growth and assimilating nutrients. By consuming epiphytes, snails can benefit the growth of submerged plants. However, the efficiency of this phytoremediation strategy may depend on the microbes associated with the plants and snails. In this study, we compared the epiphytic bacterial communities on submerged plants (Vallisneria natans and Cabomba caroliniana) and intestinal bacterial communities of a snail, Bellamya aeruginosa, found on these plants using 16S rRNA gene sequencing. Epiphytic bacterial communities were similar between the two plant species and snails shared a high proportion of snail intestinal bacterial OTUs (75%) and genera (85%) with plants they grazed on. However, significant variations of Bray-Curtis distances differentiated epiphytic and intestinal bacterial communities. In addition, between the top 50 genera shared by intestinal and epiphytic bacterial communities, more Spearman correlations were detected within bacterial communities associated with snails than between communities associated with plants (190 vs. 143), and the correlations in epiphytic bacterial networks were more concentrated on certain genera, indicating they possessed distinct bacterial networks. This suggests the bacterial communities associated with snails do not depend strongly on the plant they graze on, which may be important for better understanding the role of snails in aquatic eco-restoration.

Unraveling the ecological mechanisms of bacterial succession in epiphytic biofilms on Vallisneria natans and Hydrilla verticillata during bioremediation of phenanthrene and pyrene polluted wetland

In wetland ecosystem, the microbial succession in epiphytic biofilms of submerged macrophytes remains to be fully elucidated, especially submerged macrophytes used to remediate organic pollutants contaminated sediment. Herein, 16 S rRNA gene sequencing was used to investigate the bacterial dynamics and ecological processes in the biofilms of two typical submerged macrophytes (Vallisneria natans and Hydrilla verticillata) settled in sediment polluted by polycyclic aromatic hydrocarbons (PAHs) at two growth periods. The results presented that the variations of bacterial community in the biofilms were influenced by attached surfaces (explanation ratio: 17.30%), incubation time (32.30%) and environmental factors (39.10%). Bacterial community assembly was mainly driven by dispersal limitation which triggered more positive co-occurrence associations in microbial networks, maintaining ecological stability in the process of bioremediation of PAHs. Additionally, the functional redundancy strength of bacterial community was more affected by attached surface than incubation time. The structural equation model illustrated that community assembly drove β-diversity and explained a part of ecological functions. Environmental factors, community assembly, and β-diversity jointly affected microbial networks. Overall, our study offers new insights into the microbial ecology in biofilms attached on the submerged macrophytes settled in PAH-polluted sediment, providing important information for deeply understanding submerged macrophyte-biofilm complex and promoting sustainable phytoremediation in shallow lacustrine and marshy ecosystems.

Deciphering the diversity patterns and community assembly of rare and abundant bacterial communities in a wetland system

Water microorganisms that have distinct contributions to community dynamics, including many rare taxa and few abundant taxa, are crucial to the wetland ecosystem functions. In this study, we comprehensively investigated the diversity patterns and assembly processes of rare and abundant taxa to strengthen our understanding of ecosystem function and diversity in a wetland system. The results showed that TN and NH₃-N were the most significant factors affecting the community structure in this wetland. Functional Annotation of Prokaryotic Taxa (FAPROTAX) revealed that functions associated with nitrogen removal were the most prevalent metabolic pathways in samples of regenerated wetland (RW). Co-occurrence network analysis revealed that nonrare taxa exhibited more interactions with rare taxa than with conspecifics and some microbial hubs belonged to rare taxa, which might play an instrumental role in maintaining the stability of the community structure. We found that the assembly of rare taxa with a lower niche breadth was mainly governed by homogeneous selection, implying that their higher sensitivity of these to environmental disturbances and changes in TN played significant roles in community assembly of rare taxa. In contrast, the assembly of abundant taxa with higher niche breadth was dominated by stochastic processes (undominated process and dispersal limitation) indicating that abundant taxa had greater responsibility for maintaining community structure when exposed to environmental fluctuations. These results broaden our understanding of the microbial structure, interactions and ecological assembly mechanisms underlying microbial dynamics in aquatic ecosystems, which are crucial for the management of microorganisms in the wetlands.

Metagenomics analysis unraveled the influence of sulfate radical-mediated compost nitrogen transformation process

The mechanism of nitrogen transformation of sulfate radical (SO- 4⋅) in the process of composting is unclear. The objectives of this study were to investigate the influence of SO- 4⋅ on nitrogen biotransformation during composting and to compare the differences in physicochemical parameters and metagenomics analysis between CK (fresh dairy manure and bagasse pith) and PS (the composting raw materials added with potassium persulfate). The results indicated that SO^-₄⋅ guides electron transfer in the conversion of NH⁺₄-N to NO- 3-N and breaches the extracellular polysaccharide (EPS) structure to promote nitrogen removal. Aminomonooxygenase (AMO) and nitrate reductase (NR) levels displayed an interactive relationship between microorganisms and substrates. Metagenomics analysis revealed distinct microbial community compositions and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways between nitrification and denitrification. Correlation analysis indicated that Methanobrevibacter, Bacillus and Pseudomonas were closely related to these processes. This work demonstrates the effect of SO- 4⋅ on nitrogen cycling and retention, and possible mechanisms of nitrification and denitrification during composting.

Removal of perfluoroalkyl acids and dynamic succession of biofilm microbial communities in the decomposition process of emergent macrophytes in wetlands

Perfluoroalkyl acids (PFAAs) are emerging contaminants that pose significant environmental and health concerns. Water-sediment-macrophyte residue systems were established to clarify the removal efficiency of PFAAs, explore possible removal pathways, and profile the dynamic succession of biofilm microbial communities in the decomposition process. These systems were fortified with 12 PFAAs at three concentration levels. Iris pseudacorus and Alisma orientale were selected as the decomposing emergent macrophytes. The removal rates in the treatments with residues of I. pseudacorus (IP) and A. orientale (AO) were 34.4% to 88.9% and 36.5% to 89.9%, respectively, which were higher than those in the control groups (CG) (30.3% to 86.9%), suggesting that decomposition could alter the removal of PFAAs. Sediment made the greatest contributions (preloaded 14.5% to 77.8% of PFAAs in IP, 14.3% to 78.2% in AO, and 27.4% to 71.9% in CG). PFAAs could also be removed by macrophyte residue sorption (0.0190% to 13.0% in IP and 0.016% to 15.6% in AO) and bioaccumulation of residual biofilm (the contributions of biofilm microbes and their extracellular polymeric substances were 0.0110% to 3.93% and 0.918% to 34.4%, respectively, in IP and 0.0141% to 4.65% and 1.49% to 34.1%, respectively, in AO). Significant correlations were observed between sediment/residue adsorption and bioaccumulation of biofilm microbes, and were significantly correlated with perfluoroalkyl chain length (p < 0.05). The dynamic succession of residual biofilm microbial communities was investigated. The largest difference was found at the preliminary stage. The most similar communities were found in AO on day 70 (with specific genera Macellibacteroides and WCHB1-32) and in IP on day 35 (with specific genera Aeromonas and Flavobacterium). This study is useful to understand the removal of PFAAs during the decomposition process, providing further assistance in removing PFAAs during the life cycle of macrophytes in wetlands.

Effects of shining pondweed (Potamogeton lucens) on bacterial communities in water and rhizosphere sediments in Nansi Lake, China

Submerged macrophytes and microbial communities are important parts of lake ecosystems. In this study, the bacterial community composition in rhizosphere sediments and water from areas cultivated with (PL) and without (CK) shining pondweed (Potamogeton lucens Linn.) was investigated to determine the effects of P. lucens Linn. on the structure of the bacterial communities in Nansi Lake, China. Molecular techniques, including Illumina MiSeq and qPCR targeting of the 16S rRNA gene, were used to analyze the composition and abundance of the bacterial community. We found that bacterial alpha diversity was higher in PL water than in CK water, and the opposite trend was observed in sediment. In addition, 16S rRNA gene copy number in sediment was lower in PL than in CK. We found 30 (e.g., Desulfatiglans) and 29 (e.g., Limnohabitans) significantly different genera in sediment and water, respectively. P. lucens Linn. can change chemical properties in sediment and water and thereby affect the bacterial community. At the genus level, members of bacterial community clustered according to source (water/sediment) and area (PL/CK). Our study demonstrated that submerged macrophytes can affect the bacterial community composition in both sediment and water, suggesting that submerged macrophytes affect the transportation and cycling of nutrients in lake ecosystems.

Metagenomic analysis of bacterial communities of Wadi Namar Lake, Riyadh, Saudi Arabia

Wadi Namar lake is a new touristic attraction area in the south of Riyadh. Human activities around the lake may lead to changes in water quality with subsequent changes in microenvironment components including microbial diversity. The current study was designed to assess possible changes in bacterial communities of the water at Wadi Namar Lake. Therefore, water samples were collected from three different locations along the lake: L1 (no human activities, no plants), L2 (no human activity, some plants) and L3 (human activities, municipal wastes and some plants). The total DNA of the samples was extracted and subjected to 16S rDNA sequencing and metagenomic analysis; water pH, electrical conductivity (EC), total dissolved solids (TDS) as well as the concentration of Na+1, K+1, Cl-1 and total N were analysed. Metagenomic analysis showed variations in relative abundance of 17 phyla, 31 families, 43 genera and 19 species of bacteria between the locations. Proteobacteria was the most abundant phylum in all locations; however, its highest abundance was in L1. Planctomycete phylum was highly abundant in L1 and L3, while its abundance in L2 was low. The phyla Acidobacteria, Candidatus Saccharibacteria, Nitrospirae and Chloroflexi were associated with high TDS, EC, K+1 and Cl-1 concentrations in L3; various human activities around this location had possibly affected microbial diversity. Current study results help in recognising the structure of bacterial communities at Wadi Namar Lake in relation to their surroundings for planning to environment protection and future restoration of affected ecosystems.

Community Structure and Function of Epiphytic Bacteria Associated With Myriophyllum spicatum in Baiyangdian Lake, China

Epiphytic bacteria on the surfaces of submerged macrophytes play important roles in the growth of the host plant, nutrient cycling, and the conversion of pollutants in aquatic systems. A knowledge of the epiphytic bacterial community structure could help us to understand these roles. In this study, the abundance, diversity, and functions of the epiphytic bacterial community of Myriophyllum spicatum collected from Baiyangdian Lake in June, August, and October 2019 were studied using quantitative PCR (qPCR), high-throughput sequencing, and the prediction of functions. An analysis using qPCR showed that the epiphytic bacteria were the most abundant in October and the least abundant in August. High-throughput sequencing revealed that Proteobacteria, Gammaproteobacteria, and Aeromonas were the dominant phylum, class, and genus in all the samples. The common analyses of operational taxonomic units (OTUs), NMDS, and LDA showed that the epiphytic bacterial communities were clustered together based on the seasons. The results of a canonical correlation analysis (CCA) showed that the key water quality index that affected the changes of epiphytic bacterial community of M. spicatum was the total phosphorus (TP). The changes in abundance of Gammaproteobacteria negatively correlated with the TP. Predictive results from FAPROTAX showed that the predominant biogeochemical cycle functions of the epiphytic bacterial community were chemoheterotrophy, nitrate reduction, and fermentation. These results suggest that the epiphytic bacterial community of M. spicatum from Baiyangdian Lake varies substantially with the seasons and environmental conditions.

Submerged macrophytes recruit unique microbial communities and drive functional zonation in an aquatic system

Aquatic and wetland systems are widely used for landscapes and water regeneration. Microbiomes and submerged macrophytes (hydrophytes) play essential roles in conversions of organic and inorganic compounds in those ecosystems. The systems were extensively investigated for microbial diversities and compositions. However, little is known about how hydrophytes recruited diverse microbiota and affected functional zonation in aquatic systems. To address this issue, epiphytic leaf and root, sediment, and surrounding water samples were collected from the dragon-shape aquatic system in Beijing Olympic Park. Metagenomic DNAs were extracted and subjected to sequencing. Results showed that epiphytic leaf and root microbiomes and metabolic marker genes were remarkably different from that of surrounding environment. Twenty indicator bacterial genera for epiphytic microbiomes were identified and 50 metabolic marker genes were applied to evaluate the function of epiphytic leaf and root, water, and sediment microbiomes. Co-occurrence analysis revealed highly modularized pattern of metabolic marker genes and indicator bacterial genera related to metabolic functions. These results suggested that hydrophytes shaped microbiomes and drove functional zonation in aquatic systems. KEY POINTS: • Microbiomes of hydrophytes and their surrounding environments were investigated. • Twenty indicator bacterial genera highly specific to epiphytic biofilms were identified. • Epiphytes recruited unique microbiomes and drove functional zonation in aquatic systems.

Evaluation of microbial diversity of three recreational water bodies using 16S rRNA metagenomic approach

Surface water plays a significant role in world development by promoting economic growth and health benefits to humans and animals whose lives depend on good water quality in the ecosystem. Thus, this study investigated the differences in physical and chemical properties of surface water from two lakes (Lakes Jackson and Talquin) and a pond (Pedrick Pond). Also, the influence of environmental factors on the microbial communities that live within the water environment was examined. Genomic DNA was extracted from the water samples collected and 16S rRNA sequencing method was employed to characterize the microbial community compositions across the three locations. The results obtained suggest that the water sources met the recommended recreational water quality criteria standard for clean water. Overall, Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes were the main bacterial phyla present in the communities, while Archaea was mainly dominated by Euryachaeota. Pressure, conductivity, temperature, dissolved oxygen (DO), and pH accounted for 74.2% of the variation in the distribution of the microbial community in the three locations (P < 0.05), while 58.2% of the variation in the microbial community distribution was accounted for by pressure and conductivity. The high temperature observed in the Pedrick Pond correlated with the distribution of genera hgcl_clades and Legionella. While in Lake Talquin, water conductivity was significantly associated with the abundance of Cyanobium_PCC_6307, Sediminibacterium, and Conexibacter. The results from this study indicate that the microbial communities in the two lakes are different from the pond and all the environmental variables accounted for a significant portion of the total variation, but pressure, conductivity, and temperature are more important factors due to significant correlation with the distribution of the microbial communities.

Benthic prokaryotic microbial community assembly and biogeochemical potentials in E. coli - Stressed aquatic ecosystems during plant decomposition

Benthic microbes play a crucial role in maintaining the biogeochemical balance of aquatic ecosystems especially the material cycling during plant decomposition. However, those systems in agricultural area are always threatened by agricultural run-off containing a mass of typical pathogenic invader- Escherichia coli. It is therefore vital to clarify the turnover, assembly, and geochemical functions of the E. coli invaded benthic prokaryotic microbial community during plant decomposition. During the decaying process, the key filtering factors of benthic community assembly were NH₄⁺-N (P < 0.001), NO₂^--N (P < 0.01), and Organic-N (P < 0.05). The E. coli colonized significantly in sediments (P < 0.001) and drove the turnover of the bacterial community (P = 0.001), which enhanced archaeal dominance in the benthic microbial network. E. coli also triggered niche structural variations. The biomass (%) of benthic nutrient cycling genera including Dechloromonas, Pseudomonas, Bacteroides, Candidatus_Methanofastidiosum, and Desulfomicrobium (P < 0.05) was altered by E. coli stress. The structural equation model illustrated that E. coli critically affected the benthic microbial geochemical functions in multiple pathways (P < 0.05). Our results provide new insights into benthic prokaryotic microbial community assembly and nutrient cycling and management under pollution stress.

Comparison of Myriophyllum Spicatum and artificial plants on nutrients removal and microbial community in constructed wetlands receiving WWTPs effluents

The impacts of WWTPs effluents on nutrients removal and epiphytic microbial community in constructed wetlands dominated by submersed macrophytes remain to be fully illustrated. In this study, compared to M. Spicatum, artificial submersed macrophytes (control) generally had higher NH₄⁺-N (78.35% vs 80.52%) and TN (73.35% vs 90.25%) removal rates and similar COD (70.64% vs 70.80%) and TP (59.86% vs 60.82%) removal rates in wetlands receiving simulated effluents of WWTPs (GB18918-2002). Microbial population richness was higher in epiphytic biofilms on M. Spicatum than artificial ones, and substrates played the most decisive role in determining the microbial diversities. Network analysis revealed that there were more complex interactions among environmental parameters, bacteria and eukaryotes in M. Spicatum systems than in artificial ones. Nutrients in effluents could cause damage to M. Spicatum. The results highlight that artificial plants have better performance on effluents deep treatments than submerged plants.

Effects of Escherichia coli pollution on decomposition of aquatic plants: Variation due to microbial community composition and the release and cycling of nutrients

Determination of the effects of Escherichia coli (E. coli) pollution on agricultural pond ecosystems with vegetation at different life stages is essential for the protection of ecological functions. However, no comprehensive study has yet shown the responses of epiphytic microbial communities to E. coli invasion during plant decay. Thus, this study was conducted to clarify variation in the decay of the following aquatic plants-Myriophyllum aquaticum, Nymphaea tetragona and Phragmites australis after E. coli pollution. Exogenous E. coli especially shifted the epiphytic microbial composition and distribution of P. australis. Stronger effects of E. coli on the archaeal community (edges/nodes = 0.818 < 1, modularity = 0.654; lower clustered structure, 0.389) were found than on the bacterial community (edges/nodes = 1.538 > 1, modularity = 1.291 > 0.654; higher clustered, 0.593). During plant decomposition, E. coli weakened methanogenesis by regulating the network of core genera Methanobacterium and Methanospirillum (spearman, P <  0.05), stimulated the accumulation of organic matters in water (P <  0.05). Similarly, nitrification and denitrification increased and decreased through network regulation in relative biomass of genera Devosia and Desulfovibrio (P <  0.05), respectively. The results provided theoretical supports for eutrophication management in pond ecosystems threatened by E. coli pollution.

Biofilms attached to Myriophyllum spicatum play a dominant role in nitrogen removal in constructed wetland mesocosms with submersed macrophytes: Evidence from 15N tracking, nitrogen budgets and metagenomics analyses

The mechanisms behind nitrogen removal by the submersed macrophyte-biofilm complex in wetlands remain to be fully elucidated. This study investigated the role of Myriophyllum spicatum and the biofilm on their leaves in nitrogen removal in mesocosm experiments. ¹⁵N tracking showed that 61.9% and 30% of the ¹⁵N, respectively, was removed from the system and assimilated by the macrophyte-biofilm complex after loading with 5.4 mg L^-115N labelled NH₄⁺ for 17 days. Nitrogen budget results showed that about 0.2%, 0.2% and 3.6% of the nitrogen were emitted as water-, HCl- and NaOH-soluble nitrogen-gas species, respectively. Bacteria (76.7-91.8%) were the predominant domain in all samples, followed by eukaryotes (8.0-23.0%), archaea and viruses. Network analyses showed that there were positive- and negative-correlative relationships among nitrogen-cycling genes and nitrifiers and denitrifiers. Our data highlight the important role of biofilm on submersed macrophytes for nitrogen removal.

Community composition and correlations between bacteria and algae within epiphytic biofilms on submerged macrophytes in a plateau lake, southwest China

Epiphytic biofilms are complex matrix-enclosed communities comprising large numbers of bacteria and algae, which play an important role in the biogeochemical cycles in aquatic systems. However, little is known about the correlations that occur between these communities or the relative impact of environmental factors on their composition. In this study, epiphytic biofilms on three different aquatic plants were sampled in a typical plateau lake (Caohai, southwest China) in July and November of 2018. Bacterial diversity was assessed using Miseq sequencing approaches and algal communities were assessed using light microscopy. Gammaproteobacteria (54.64%), Bacteroidetes (17.50%) and Firmicutes (13.99%) were the dominant bacterial taxa and Chlorophyta (47.62%), Bacillariophyta (28.57%) and Euglenophyta (19.05%) were the dominant algae. The alpha diversity values of the epiphytic bacterial and algal communities were greater during the macrophyte decline period (November) than during the growth period (July). Microbial community composition was significantly affected by abiotic factors (water temperature, NH₄⁺, pH or TP) and biotic factors (algae or bacteria). Interestingly, in July and November, the epiphytic algal community dissimilarity was stronger than that observed for bacterial community dissimilarity, suggesting that bacterial community dissimilarity may increase more slowly with environmental change than algal community dissimilarity. Furthermore, association network analysis revealed complex correlations between algal biomass and bacteria phylotype, and that 67.83% of correlations were positive and 32.17% were negative. This may indicate that facilitative correlations between algae and bacteria are predominant in epiphytic biofilms. These results provide new information on algal-bacterial correlations as well as the possible mechanisms that drive variations in the microbial community in epiphytic biofilms in freshwater lakes.

Bacterial succession in epiphytic biofilms and deciduous layer sediments during Hydrilla verticillata decay: A field investigation

Submersed macrophytes decay is an important natural process and has important role in mass and energy flow in aquatic ecosystems. However, little is known about the dynamical changes in nutrients release and bacterial community during submersed macrophyte decay in natural environment. In this study, a field observation was conducted in a wetland dominated with Hydrilla verticillata for 36 days. Increase of H₂O₂ and malondialdehyde (MDA) content and decrease of soluble proteins concentration were detected in leaves during H. verticillata decay. Meanwhile, ammonium-N, soluble microbial products (SMP) and TOC concentration increased in overlying water. According to bacterial 16S rRNA Illumina sequencing analysis, the Shannon values were lower in epiphytic biofilms than deciduous layer sediments. The relative abundances of Proteobacteria, Cyanobacteria and Actinobacteria were higher in epiphytic biofilms than in deciduous layer sediments (P < 0.05). Co-occurrence network analyses showed that a total of 578 and 845 pairs of correlations (|r| > 0.6) were identified from 122 and 112 genera in epiphytic biofilms and deciduous layer sediments, respectively. According to co-occurrence patterns, eight hubs were mainly from phyla Proteobacteria, Acidobacteria and Parcubacteria in epiphytic biofilms; while 37 hubs from the 14 phyla (Proteobacteria, Bacteroidetes, Acidobacteria, Chloroflexi, et al.) were detected in deciduous layer sediments. Our results indicate that bacterial community in deciduous layer sediments was more susceptible than in epiphytic biofilms during decay process. These data highlight the role of microbial community in deciduous layer sediments on nutrients removal during H. verticillata decay and will provide useful information for wetland management.

Characterization and co-occurrence of microbial community in epiphytic biofilms and surface sediments of wetlands with submersed macrophytes

Microbes in epiphytic biofilms and surface sediments play crucial roles in the biogeochemical cycles in wetlands. However, little is known about the compositions of microbial community in wetlands dominated with submersed macrophytes. In this study, bacterial and eukaryotic community in epiphytic biofilms and surface sediments were investigated in wetlands with artificial plants and Myriophyllum verticillatum from September (~27 °C) to January (~9 °C). A total of 30 (including 13 bacterial and 17 eukaryotic) and 34 (including 14 bacterial and 20 eukaryotic) phyla were detected in epiphytic biofilms and sediments, respectively. Microbial community in epiphytic biofilms shifted with decreasing temperature, and biofilms on M. verticillatum were generally similar to those on artificial plants. Though the OTUs and Shannon values were significantly higher in sediments than epiphytic biofilms (p < 0.05), numbers of strongly correlated edges detected in biofilms (64 nodes with 182 edges) were at least three times of those in sediments (40 nodes with 57 edges) as revealed by co-occurrence networks analysis (|r| > 0.7, p < 0.05). These data suggest that there were complex interactions among microbes in epiphytic biofilms than sediments. Positive relationships among microbes revealed the predation, symbiosis, parasitism relationships and the collective degradation of organic matter, while negative ones may be ascribed to their different lifestyles. These results highlight that artificial plants play a similar role as submersed macrophytes as microbial carriers and can be potentially used an alternative substitutes to submersed macrophytes in wetlands.