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

Microbiome shifts elicited by ornamental lighting of granite facades identified by MinION sequencing

Night-time outdoor illumination in combination with natural sunlight can influence the visible phototrophic colonizers (mainly algae) growing on stone facades; however, the effects on the microbiome (invisible to the naked eye) are not clear. The presence of stone-dwelling microbes, such as bacteria, diatoms, fungi, viruses and archaea, drives further biological colonization, which may exacerbate the biodeterioration of substrates. Considering the microbiome is therefore important for conservation of the built heritage. The impact of the following types of lighting on the relative abundance and diversity of the microbiome on granite ashlars was evaluated in a year-long outdoor pilot study: no lighting; lighting with a metal halide lamp (a traditional lighting system currently used to illuminate monuments); and lighting with a novel LED lamp (an environmentally sound prototype lamp with a biostatic effect, halting biological colonization by phototrophs, currently under trial). Culturable fractions of microbiome and whole-genome sequencing by metabarcoding with Oxford Nanopore Sequencing (MinION) was conducted for bacteria and fungi in order to complement both community characterization strategies. In addition, the possible biodeteriorative profiles of the isolated strains, relative to calcium carbonate precipitation/solubilisation and iron oxidation/reduction, were investigated by plate assays. Alpha and beta diversity indexes were also determined, along with the abundance of biocide and antibiotic resistance genes. Culture-dependent microbiological analysis failed to properly show changes in community composition, for which metagenomic approaches like MinION are better suited. Thus, MinION analysis identified shifts in the granite microbiome elicited by ornamental lighting. The novel LED lamp with the biostatic effect on phototrophs caused an increase in the diversity of bacteria and fungi. In this case, the microbiome was more similar to that in the unlit samples. In the samples illuminated by the metal halide lamp, dominance of bacteria was favoured and the presence of fungi was negligible.

Non-pathogenic microbiome associated to aquatic plants and anthropogenic impacts on this interaction

The microbiota associated with aquatic plants plays a crucial role in promoting plant growth and development. The structure of the plant microbiome is shaped by intricate interactions among hosts, microbes, and environmental factors. Consequently, anthropogenic pressures that disrupt these interactions can indirectly impact the ecosystem services provided by aquatic plants, such as CO2 fixation, provision of food resources, shelter to animals, nutrient cycling, and water purification. Presently, studies on plant-microbiota interactions primarily focus on terrestrial hosts and overlook aquatic environments with their unique microbiomes. Therefore, there is a pressing need for a comprehensive understanding of plant microbiomes in aquatic ecosystems. This review delves into the overall composition of the microbiota associated with aquatic plant, with a particular emphasis on bacterial communities, which have been more extensively studied. Subsequently, the functions provided by the microbiota to their aquatic plants hosts are explored, including the acquisition and mobilization of nutrients, production of auxin and related compounds, enhancement of photosynthesis, and protection against biotic and abiotic stresses. Additionally, the influence of anthropogenic stressors, such as climate change and aquatic contamination, on the interaction between microbiota and aquatic plants is discussed. Finally, knowledge gaps are highlighted and future directions in this field are suggested.

Regional differences in lead (Pb) and tetracycline (TC) binding behavior of sediment dissolved organic matter (SDOM): Effects of DOM heterogeneity and microbial degradation

Lake Nansi, primarily dominated by macrophytes, faces threats from heavy metals and antibiotics due to human activity. This study investigated sediment dissolved organic matter (SDOM) characteristics and complexation of lead (Pb) and tetracycline (TC) in barren zone (BZ) and submerged macrophytes zone (PZ). Additionally, a microbial degradation experiment was conducted to examine its impact on the regional variations in complexation. SDOM abundance and protein-like materials in PZ was significantly greater than in BZ, indicating a probable contribution from the metabolism and decomposition of submerged macrophytes. Both zones exhibited a higher affinity of SDOM for Pb compared to TC, with all four components participating in Pb complexation. Protein-like materials in PZ had a higher binding ability (LogKPb=4.19 ± 1.07, LogKTC=3.89 ± 0.67) than in BZ (LogKPb=3.98 ± 0.61, LogKTC=3.69 ± 0.13), suggesting a potential presence of organically bound Pb and TC due to the higher abundance of protein-like materials in PZ. Although microbial communities differed noticeably, the degradation patterns of SDOM were similar in both zones, affecting the binding ability of SDOM in each. Notably, the fulvic-like component C4 emerged as the dominant binding material for both Pb and TC in both zones. Degradation might increase the amount of organically bound TC due to the increase in the LogKTC.

Interspecific Differences in Carbon and Nitrogen Metabolism and Leaf Epiphytic Bacteria among Three Submerged Macrophytes in Response to Elevated Ammonia Nitrogen Concentrations

Submerged macrophytes in eutrophic aquatic environments adapt to changes in ammonia nitrogen (NH4-N) levels by modifying their levels of free amino acids (FAAs) and soluble carbohydrates (SCs). As symbionts of submerged macrophytes, epiphytic bacteria have obvious host specificity. In the present study, the interspecific differences in the FAA and SC contents of Hydrilla verticillata (Linn. f.) Roylep, Vallisneria natans Hara and Chara braunii Gmelin and their leaf epiphytic bacterial communities were assessed in response to increased NH4-N concentrations. The results revealed that the response of the three submerged macrophytes to NH4-N stress involved the consumption of SCs and the production of FAAs. The NH4-N concentration had a greater impact on the variation in the FAA content, whereas the variation in the SC content was primarily influenced by the species. At the phylum level, the relative abundance of Nitrospirota on the leaves exhibited specific differences, with the order H. verticillata > V. natans > C. braunii. The dominant genera of epiphytic bacteria with denitrification effects on V. natans, H. verticillata and C. braunii leaves were Halomonas, Acinetobacter and Bacillus, respectively. When faced with NH4-N stress, the variation in epiphytic bacterial populations associated with ammonia oxidation and denitrification among submerged macrophytes could contribute to their divergent responses to heightened nitrogen levels.

Macrophyte coverage drives microbial community structure and interactions in a shallow sub-tropical lake

Shallow lakes are typically dominated by macrophytes, which have important functional roles regulating trophic conditions and creating biological habitat. Macrophytes have been shown to strongly influence water chemistry and shape microbial communities in shallow lakes. In Florida, many large, shallow lakes are dominated by alien invasive, submersed macrophytes, such as hydrilla (Hydrilla verticillata [L.F.] Royle) and are intensively managed to reduce infestations and contain the spread of these alien invasive macrophytes. In this study, we investigated the effects of large (40 ha) herbicidal and mechanical control treatments on a large lake located in Central Florida that resulted in the reduction of Hydrilla and concomitant changes in water chemistry and microbial communities (both bacteria and protists [microbial eukaryotes]). We observed a considerable decrease in macrophyte coverage associated with plant control treatments as well as a temporal change in macrophyte coverage in Lake Tohopekaliga. We found that changes in macrophyte coverage, regardless of treatment type, significantly affected the water chemistry of the lake, resulting in a sharp increase of chlorophyll a concentration as well as an increase in turbidity with the decrease of macrophyte coverage. Moreover, the decline in macrophytes led to decreases in microbial community diversity with over-representation of phototrophic functional groups. Specifically, we observed an increase in cyanobacteria with the decrease in macrophyte coverage. Our study highlights the advantages and disadvantages of macrophyte control. Although there was an initial decrease in macrophyte coverage associated with the chemical and mechanical control of aquatic plants, after a few months, we found a considerable increase in coverage. In addition, the increase of cyanobacterial relative abundance demonstrates the possible consequences of aquatic plant control such as cyanobacterial blooms if there is a continued decline of macrophytes.

Microbial community structure and diversity attached to the periphyton in different urban aquatic habitats

Periphyton is a complex community composed of diverse prokaryotes and eukaryotes; understanding the characteristics of microbial communities within periphyton becomes crucial for biogeochemical cycles and energy dynamics of aquatic ecosystems. To further elucidate the community characteristics of periphyton across varied aquatic habitats, including unpolluted ecologically restored lakes, aquaculture ponds, and areas adjacent to domestic and industrial wastewater treatment plant outfalls, we explored the composition and diversity of prokaryotic and eukaryotic communities in periphyton by employing Illumina MiSeq sequencing. Our findings indicated that the prokaryotic communities were predominantly composed of Proteobacteria (40.92%), Bacteroidota (21.01%), and Cyanobacteria (10.12%), whereas the eukaryotic communities were primarily characterized by the dominance of Bacillariophyta (24.09%), Chlorophyta (20.83%), and Annelida (15.31%). Notably, Flavobacterium emerged as a widely distributed genus among the prokaryotic community. Unclassified_Tobrilidae exhibited higher abundance in unpolluted ecologically restored lakes. Chaetogaster and Nais were enriched in aquaculture ponds and domestic wastewater treatment plant outfall area, respectively, while Surirella and Gomphonema dominated industrial sewage treatment plant outfall area. The alpha diversity of eukaryotes was higher in unpolluted ecologically restored lakes. pH and nitrogen content (NO 2 - - N ,NO 3 - - N , and TN) significantly explained the variations for prokaryotic and eukaryotic community structures, respectively. Eukaryotic communities exhibited a more pronounced response to habitat variations compared to prokaryotic communities. Moreover, the association networks revealed an intensive positive correlation between dominant Bacillariophyta and Bacteroidota. This study provided useful data for identifying keystone species and understanding their ecological functions.

Interactions between water quality and microbes in epiphytic biofilm and superficial sediment of lake in trophic agriculture area

Epiphytic and superficial sediment biofilm-dwelling microbial communities play a pivotal role in water quality regulation and biogeochemical cycling in shallow lakes. However, the interactions are far from clear between water physicochemical parameters and microbial community on aquatic plants and in surface sediments of lake in trophic agriculture area. This study employed Illumina sequencing, Partial Least Squares Path Modeling (PLS-PM), and physico-chemical analytical methods to explore the interactions between water quality and microbes (bacteria and eukaryotes) in three substrates of trophic shallow Lake Cyohoha North, Rwanda. The Lake Cyohoha was significantly polluted with total phosphorus (TP), total nitrogen (TN), nitrate nitrogen (NO3-N), and ammonia nitrogen (NH3-N) in the wet season compared to the dry season. PLS-PM revealed a strong positive correlation (+0.9301) between land use types and physico-chemical variables in the rainy season. In three substrates of the trophic lake, Proteobacteria, Cyanobacteria, Firmicutes, and Actinobacteria were dominant phyla in the bacterial communities, and Rotifers, Platyhelminthes, Gastrotricha, and Ascomycota dominated in microeukaryotic communities. As revealed by null and neutral models, stochastic processes predominantly governed the assembly of bacterial and microeukaryotic communities in biofilms and surface sediments. Network analysis revealed that the microbial interconnections in Ceratophyllum demersum were more stable and complex compared to those in Eichhornia crassipes and sediments. Co-occurrence network analysis (|r| > 0.7, p < 0.05) revealed that there were complex interactions among physicochemical parameters and microbes in epiphytic and sediment biofilms, and many keystone microbes on three substrates played important role in nutrients removal, food web and microbial community stable. These findings emphasize that eutrophic water influence the structure, composition, and interactions of microbes in epiphytic and surface sediment biofilms, and provided new insights into the interconnections between water quality and microbial community in presentative substrates in tropical lacustrine ecosystems in agriculturally polluted areas. The study provides useful information for water quality protection and aquatic plants restoration for policy making and catchment management.

How to identify biofouling species in marine and freshwater

The identification and management of biofouling remain pressing challenges in marine and freshwater ecosystems, with significant implications for environmental sustainability and industrial operations. This comprehensive review synthesizes the current state-of-the-art in biofouling identification technologies, examining eight prominent methodologies: Microscopy Examination, Molecular Biology, Remote Sensing, Community Involvement, Ecological Methods, Artificial Intelligence, Chemical Analysis, and Macro Photography. Each method is evaluated for its respective advantages and disadvantages, considering factors such as precision, scalability, cost, and data quality. Furthermore, the review identifies current obstacles that inhibit the optimal utilization of these technologies, ranging from technical limitations and high operational costs to issues of data inconsistency and subjectivity. Finally, the review posits a future outlook, advocating for the development of integrated, standardized systems that amalgamate the strengths of individual approaches. Such advancement will pave the way for more effective and sustainable strategies for biofouling identification and management.

Analysis of diversity and function of epiphytic bacterial communities associated with macrophytes using a metagenomic approach

Epiphytic bacteria constitute a vital component of aquatic ecosystems, pivotal in regulating elemental cycling. Despite their significance, the diversity and functions of epiphytic bacterial communities adhering to various submerged macrophytes remain largely unexplored. In this study, we employed a metagenomic approach to investigate the diversity and function of epiphytic bacterial communities associated with six submerged macrophytes: Ceratophyllum demersum, Hydrilla verticillata, Myriophyllum verticillatum, Potamogeton lucens, Stuckenia pectinata, and Najas marina. The results revealed that the predominant epiphytic bacterial species for each plant type included Pseudomonas spp., Microbacterium spp., and Stenotrophomonas rhizophila. Multiple comparisons and linear discriminant analysis effect size indicated a significant divergence in the community composition of epiphytic bacteria among the six submerged macrophytes, with 0.3-1% of species uniquely identified. Epiphytic bacterial richness associated with S. pectinata significantly differed from that of both C. demersum and H. verticillata, although no significant differences were observed in diversity and evenness. Functionally, notable variations were observed in the relative abundances of genes associated with carbon, nitrogen, and phosphorus cycling within epiphytic bacterial communities on the submerged macrophyte hosts. Among these communities, H. verticillata exhibited enrichment in genes related to the 3-hydroxypropionate bicycle and nitrogen assimilation, translocation, and denitrification. Conversely, M. verticillatum showcased enrichment in genes linked to the reductive citric acid cycle (Arnon-Buchanan cycle), reductive pentose phosphate cycle (Calvin cycle), polyphosphate degradation, and organic nitrogen metabolism. In summary, our findings offer valuable insights into the diversity and function of epiphytic bacteria on submerged macrophyte leaves, shedding light on their roles in lake ecosystems.

Temporal variations in reactive oxygen species in biofilms of submerged macrophytes: The key role of microbial metabolism mediated by oxygen fluctuations

Reactive oxygen species (ROS) play a crucial role in the biogeochemistry of aquatic environments, yet their occurrence and accumulation in the biofilm of submerged macrophytes have been poorly documented. Herein, we first investigated the light-dark cycling fluctuations of biofilm microenvironment and the temporal variations of a representative ROS (O2•-) during biofilm succession on the macrophyte leaves and subsequently quantified the photochemical processes in biofilms. The sustained production of O2•- exhibited a distinct rhythmic fluctuation from 32.49 ± 0.56 μmol/kg to 72.56 ± 0.92 μmol/kg FW, which simultaneously fluctuated with the dissolved oxygen, redox potential, and pH, all driven by the alternating oxic-anoxic conditions of biofilms. The intensities of O2•- and ROS firstly increased and then decreased throughout biofilm succession. The O2•- concentrations in biofilms from different waters followed the order of rural river water > landscape lake water > aquaculture pond water, and the leaf photosynthesis and microbial community played a key role. ROS production was significantly associated with Actinobacteria, Proteobacteria and Bacteroidetes, with contributions of 44.6%, 32.8%, and 15.2%, respectively. Partial least squares path modeling structural equation analysis showed that ROS production in leaf biofilms was mainly related to the microenvironment and microbial metabolism. These findings will facilitate the development of ecological restoration strategies in aquatic environments.

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

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

Algal or bacterial community: Who can be an effective indicator of the impact of reclaimed water recharge in an urban river

Reclaimed water has been widely utilized for water resource replenishment, yet little is known regarding its impacts on various microorganisms in the receiving water. To address this knowledge gap, we systematically investigated the responses of bacteria and algae to the recharge of reclaimed water by using the high-throughput sequencing technology in the urban Chaobai River. After the inputs of reclaimed water, lower contents of NO2--N, NH4+-N, and TP were observed in the downstream section compared to that of upstream without reclaimed water, indicating that reclaimed water could improve the water quality of the receiving water. Correspondingly, both bacterial and algal communities showed the decreased network complexity in the downstream section, but many common freshwater bacteria and typical bloom-forming algae were dominant in the downstream, potentially suggesting that algae were more sensitive to the local environmental conditions. More importantly, although nitrogen and phosphorus served as the paramount factors in shaping both bacterial and algal communities, environmental selection contributed more to algal rather than bacterial community, and simultaneously algal variations could further affect bacterial dynamics in the urban river. Overall, these findings revealed distinct characteristics of bacteria and algae in responding to the reclaimed water recharge, highlighting the superiority of algae in indicating environmental changes, especially in monitoring and regulating the replenishment of reclaimed water in urban rivers.

Response of dissolved organic matter (DOM) and microbial community to submerged macrophytes restoration in lakes: A review

Microorganisms play a crucial role in the biogeochemical processes of Dissolved Organic Matter (DOM), and the properties of DOM also significantly influence changes in microbial community characteristics. This interdependent relationship is vital for the flow of matter and energy within aquatic ecosystems. The presence, growth state, and community characteristics of submerged macrophytes determine the susceptibility of lakes to eutrophication, and restoring a healthy submerged macrophyte community is an effective way to address this issue. However, the transition from eutrophic lakes dominated by planktic algae to medium or low trophic lakes dominated by submerged macrophytes involves significant changes. Changes in aquatic vegetation have greatly affected the source, composition, and bioavailability of DOM. The adsorption and fixation functions of submerged macrophytes determine the migration and storage of DOM and other substances from water to sediment. Submerged macrophytes regulate the characteristics and distribution of microbial communities by controlling the distribution of carbon sources and nutrients in the lake. They further affect the characteristics of the microbial community in the lake environment through their unique epiphytic microorganisms. The unique process of submerged macrophyte recession or restoration can alter the DOM-microbial interaction pattern in lakes through its dual effects on DOM and microbial commu-----nities, ultimately changing the stability of carbon and mineralization pathways in lakes, such as the release of methane and other greenhouse gases. This review provides a fresh perspective on the dynamic changes of DOM and the role of the microbiome in the future of lake ecosystems.

Bacteria and microalgae associations in periphyton-mechanisms and biotechnological opportunities

Phototrophic and heterotrophic microorganisms coexist in complex and dynamic structures called periphyton. These structures shape the biogeochemistry and biodiversity of aquatic ecosystems. In particular, microalgae-bacteria interactions are a prominent focus of study by microbial ecologists and can provide biotechnological opportunities for numerous applications (i.e. microalgal bloom control, aquaculture, biorefinery, and wastewater bioremediation). In this review, we analyze the species dynamics (i.e. periphyton formation and factors determining the prevalence of one species over another), coexisting communities, exchange of resources, and communication mechanisms of periphytic microalgae and bacteria. We extend periphyton mathematical modelling as a tool to comprehend complex interactions. This review is expected to boost the applicability of microalgae-bacteria consortia, by drawing out knowledge from natural periphyton.

A limited overlap of interactions between the bacterial community of water and sediment in wetland ecosystem of the Yellow River floodplain

Introduction

Aquatic ecosystems in floodplains provide homes for a variety of active bacterial populations. However, the coexistence pattern of bacterial communities of water and sediment in these ecosystems is unclear.

Methods

In the present study, Illumina Mi-Seq sequencing were to assess bacteria's co-occurrence patterns in the water and sediment of different time dynamics and plant communities of the Yellow River floodplain ecosystem.

Results and discussion

The results showed that compared to water, the α-diversity of the bacterial community was way greater in sediment. The bacterial community structure significantly differed between water and sediment, and there was a limited overlap of interactions between the bacterial community of water and sediment. In addition, bacteria in water and sediment coexisting show different temporal shifts and community assembly patterns. The water was selected for specific groups of microorganisms that assemble over time in a non-reproducible and non-random way, whereas the sediment environment was relatively stable, and the bacterial communities were gathered randomly. The depth and plant cover significantly influenced the structure of a bacterial community in the sediment. The bacterial community in sediment formed a more robust network than those in water to cope with external changes. These findings improved our comprehension of the ecological trends of water and sediment bacterium colonies coexisting enhanced the biological barrier function, and the capacity of floodplain ecosystems to provide services and offered support for doing so.

Environmental behaviors of emerging contaminants in freshwater ecosystem dominated by submerged plants: A review

Persistent exposure of emerging contaminants (ECs) in freshwater ecosystem has initiated intense global concerns. Freshwater ecosystem dominated by submerged plants (SP-FES) has been widely constructed to control eutrophic water. However, the environmental behaviors (e.g. migration, transformation, and degradation) of ECs in SP-FES have rarely been concerned and summarized. This review briefly introduced the sources of ECs, the pathways of ECs entering into SP-FES, and the constituent elements of SP-FES. And then the environmental behaviors of dissolved ECs and refractory solid ECs in SP-FES were comprehensively summarized, and the feasibility of removing ECs from SP-FES was critically evaluated. Finally, the challenges and perspectives on the future development for ECs removal from SP-FES were prospected, giving possible research gaps and key directions. This review will provide theoretical and technical support for the effective removal of ECs in freshwater ecosystem, especially in SP-FES.

Effects of submerged macrophytes (Elodea nuttallii) on water quality and microbial communities of largemouth bass (Micropterus salmoides) ponds

Traditional aquaculture ponds are one of the most vulnerable ecosystems; thus, ecological aquaculture is increasingly valued for its beneficial ecological properties and ecosystem services. However, little is known about ecological aquaculture of largemouth bass with submerged vegetation. Here, we designed three ecological ponds of cultured largemouth bass with submerged macrophytes (the EM group) and three ponds with traditional aquaculture (the M group) to reveal the response of water quality, and phytoplankton and bacterial communities, to submerged macrophyte bioremediation during a 90-day culture period. We observed that Cyanobacterial outbreak occurred in the M group ponds from day 7 to the end of the experiment; however, there were no Cyanobacterial blooms in the EM group ponds throughout the culture period. Compared with the M group ponds, the EM group ponds, which had submerged hydrophytes, had significantly decreased concentrations of TP, TN, and COD_Mn, but significantly increased DO concentrations throughout the experimental period. Moreover, ecological aquaculture with submerged macrophytes showed strong effects on the phytoplankton and bacterial community compositions. In particular, the M group ponds had higher phytoplankton density and mainly included Cyanobacteria, whereas the EM group had lower phytoplankton density and mainly included Chlorophyta. Moreover, higher alpha diversity, as determined by Ace and Simpson index values, was detected for bacterial communities in the EM group ponds. Furthermore, PCoA clearly grouped the bacterial communities according to the two culture modes throughout the culture period. These results indicate that ecological aquaculture with submerged macrophytes can improve water quality, control Cyanobacterial blooms, and affect the diversity and composition of bacterial communities. These valuable effects seem to be beneficial and consistent to maintaining aquaculture ecosystem stability.

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

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

Phyllosphere eukaryotic microalgal communities in rainforests: Drivers and diversity

Phyllosphere algae are common in tropical rainforests, forming visible biofilms or spots on plant leaf surfaces. However, knowledge of phyllosphere algal diversity and the environmental factors that drive that diversity is limited. The aim of this study is to identify the environmental factors that drive phyllosphere algal community composition and diversity in rainforests. For this purpose, we used single molecule real-time sequencing of full-length 18S rDNA to characterize the composition of phyllosphere microalgal communities growing on four host tree species (Ficus tikoua, Caryota mitis, Arenga pinnata, and Musa acuminata) common to three types of forest over four months at the Xishuangbanna Tropical Botanical Garden, Yunnan Province, China. Environmental 18S rDNA sequences revealed that the green algae orders Watanabeales and Trentepohliales were dominant in almost all algal communities and that phyllosphere algal species richness and biomass were lower in planted forest than in primeval and reserve rainforest. In addition, algal community composition differed significantly between planted forest and primeval rainforest. We also found that algal communities were affected by soluble reactive phosphorous, total nitrogen, and ammonium contents. Our findings indicate that algal community structure is significantly related to forest type and host tree species. Furthermore, this study is the first to identify environmental factors that affect phyllosphere algal communities, significantly contributing to future taxonomic research, especially for the green algae orders Watanabeales and Trentepohliales. This research also serves as an important reference for molecular diversity analysis of algae in other specific habitats, such as epiphytic algae and soil algae.

Similar assembly mechanisms but distinct co-occurrence patterns of free-living vs. particle-attached bacterial communities across different habitats and seasons in shallow, eutrophic Lake Taihu

Eutrophication due to nitrogen and phosphorus input is an increasing problem in lake ecosystems. Free-living (FL) and particle-attached (PA) bacterial communities play a primary role in mediating biogeochemical processes in these lakes and in responding to eutrophication. However, knowledge of factors governing function, assembly mechanisms, and co-occurrence patterns of these communities remain poorly understood and are key challenges in microbial ecology. To address this knowledge gap, we collected 96 samples from Lake Taihu across four seasons and investigated the bacterial community using 16S rRNA gene sequencing. Our results demonstrate that the α-diversity, β-diversity, community composition, and functional composition of FL and PA bacterial communities exhibited differing spatiotemporal dynamics. FL and PA bacterial communities displayed similar distance-decay relationships across seasons. Deterministic processes (i.e., environmental filtering and species interaction) were the primary factors shaping community assembly in both FL and PA bacteria. Similar environmental factors shaped bacterial community structure while different environmental factors drove bacterial functional composition. Habitat filtering influenced enrichment of bacteria within specific functional groups. Among them, the FL bacterial community appeared to play a critical role in methane-utilization, whereas the PA bacteria contributed more to biogeochemical cycling of carbon. FL and PA bacterial communities exhibited distinct co-occurrence pattern across different seasons. In the FL network, Methylotenera and Methylophilaceae were identified as keystone taxa, while Burkholderiaceae and the hgcI clade were keystone taxa in the PA network. The PA bacterial community appeared to possess greater stability in the face of environmental change than did FL counterparts. These results broaden our knowledge of the driving factors, co-occurrence patterns, and assembly processes in FL and PA bacterial communities in eutrophic ecosystems and provide improved insight into the underlying mechanisms responsible for these results.

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.

Gradient rise in seepage pollution levels in tailings ponds shapes closer linkages between phytoplankton and bacteria

A large number of tailings ponds formed by slag accumulation have become serious environmental hazards. Spatially high potential energy and long-term accumulation may result in gradient-changing seepage pollution. The assemblages of phytoplankton and bacteria are widely used as assessment indicators. In this study, we investigate the changes in phytoplankton and bacterial assemblages in tailing pollution. The results showed that there are temporal and spatial variabilities in seepage pollution. The abundance and diversity of phytoplankton and bacteria decreased with increasing pollution. However, Synedra acus (diatom) and Polynucleobacter (bacteria) were positively correlated with pollution levels (r = 0.37, P < 0.05; r = 0.24, P < 0.05). Heavy metals are the main contributors to bacterial changes (16.46%), while nutrients are for algae (13.24%). Tailings pond pollution reduced the number of phytoplankton and bacterial linkages. However, more pollution broke the originally independent modules of phytoplankton and bacteria, and they produced more positive correlations (79.39%; 87.68%). Microcystis sp. and Limnobacter were the key nodes of the co-occurrence network in the polluted areas. Exploring the interactions between bacteria and phytoplankton within different pollution levels could provide insights into biological interaction patterns and the bioremediation of tailings ponds.

Spatiotemporal changes of bacterial communities during a cyanobacterial bloom in a subtropical water source reservoir ecosystem in China

Cyanobacterial blooms, which not only threaten the health and stability of aquatic ecosystems but also influence the microbial community within, emerges as one of the most concerning problems in China. However, how cyanobacterial blooms affect the spatiotemporal variation of aquatic microbial communities remains relatively unclear. In this study, we used high-throughput sequencing to investigate how the cyanobacterial and bacterial community spatiotemporally vary along with main cyanobacterial bloom phases in upstream rivers of a eutrophicated water source reservoir. Both cyanobacterial and bacterial diversities in each river were significantly lower (P < 0.05) during the bloom outbreak phase, showing the apparent influence of cyanobacterial bloom. Dominant cyanobacterial taxa included Cyanobacteriales and Synechococcales, and dominant bacterial taxa comprised Acinetobacter, CL500-29, hgcI clade, Limnohabitans, Flavobacterium, Rhodoluna, Porphyrobacter, Rhodobacter, Pseudomonas, and Rhizobiales, whose changes of relative abundance along with the bloom indicated distinct community composition. Non-metric multidimensional scaling analysis proved that community composition had significant difference amongst bloom phases. Linear discriminant analysis (LDA) with LDA effect size analysis (LEfSe) identified unique dominant cyanobacterial and bacterial OTUs at different phases in each river, indicating spatiotemporal variations of communities. Canonical correlation analysis or redundancy analysis revealed that at different bloom phases communities of each river had distinct correlation patterns with the environmental parameters (temperature, ammonium, nitrate, and total phosphorus etc.), implying the spatial variations of microbial communities. Overall, these results expand current understanding on the spatiotemporal variations of microbial communities due to cyanobacterial blooms. Microbial interactions during the bloom may shed light on controlling cyanobacterial blooms in the similar aquatic ecosystems.

Community structure and function of epiphytic bacteria attached to three submerged macrophytes

In aquatic ecosystems, large amounts of epiphytic bacteria living on the leaf surfaces of submerged macrophytes play important roles in affecting plant growth and biogeochemical cycling. The restoration of different submerged macrophytes has been considered an effective measure to improve eutrophic lakes. However, the community ecology of epiphytic bacteria is far from well understood for different submerged macrophytes. In this study, we used quantitative PCR, 16S rRNA gene high-throughput sequencing and functional prediction analysis to explore the structure and function of epiphytic bacteria in an aquatic ecosystem recovered by three submerged macrophytes (Hydrilla verticillata, Vallisneria natans and Potamogeton maackianus) during two growth periods. The results showed that the community compositions and functions of epiphytic bacterial communities on the submerged macrophyte hosts were different from those of the planktonic bacterial communities in the surrounding water. The alpha diversity of the epiphytic bacterial community was significantly higher in October than in July, and the community compositions and functions differed significantly in July and October. Among the three submerged macrophytes, the structures and functions of the epiphytic bacterial community exhibited obvious differences, and some specific taxa were enriched on the biofilms of the three plants. The alpha diversity and the abundance of functions related to nitrogen and phosphorus transformation were higher in the epiphytic bacteria of P. maackianus. In summary, these results provide clues for understanding the distribution and formation mechanisms of epiphytic bacteria on submerged macrophyte leaves and their roles in freshwater ecosystems.

The Growth of Vallisneria natans and Its Epiphytic Biofilm in Simulated Nutrient-Rich Flowing Water

This paper investigates the effects of water flow on the growth and physiological indicators of the submerged macrophyte, Vallisneria natans, and the bacteria and algae community composition on its epiphytic biofilm-covered leaves. The authors set up a simulated flowing water laboratory experiment testing high nitrogen (N) and phosphorus (P) concentrations. Total chlorophyll and dissolved oxygen (DO) was significantly enhanced, and turbidity was reduced, thereby accelerating the growth of V. natans. These experiments were compared to another set of observations on a static group. The accumulation of malonaldehyde (MDA) in the dynamic groups was significantly higher than that in the static group. As an antioxidant stress response, the total superoxide dismutase (T-SOD) was also induced in plants exposed to nutrient-rich flowing water. The results of 16S rRNA high-throughput sequencing analyses showed that the water flow increased the bacteria community diversity of biofilm-producing bacteria with N and P removing bacteria, carbon cycle bacteria, and plant growth-promoting rhizobacteria on the epiphytic biofilm. This research determined that water flow alleviates the adverse effects of eutrophication when V. natans grows in water containing high N and P concentrations. Water flow also inhibits the growth of cyanobacteria (also referred to as blue-green algae) in epiphytic biofilm. The ecological factor of water flow, such as water disturbance and aeration measures, could alleviate the adverse effect of eutrophic water by providing a new way to restore submerged macrophytes, such as V. natans, in eutrophic water.

Towards understanding mechanisms and functional consequences of bacterial interactions with members of various kingdoms in complex biofilms that abound in nature

The microbial world represents a phenomenal diversity of microorganisms from different kingdoms of life which occupy an impressive set of ecological niches. Most, if not all, microorganisms once colonise a surface develop architecturally complex surface-adhered communities which we refer to as biofilms. They are embedded in polymeric structural scaffolds serve as a dynamic milieu for intercellular communication through physical and chemical signalling. Deciphering microbial ecology of biofilms in various natural or engineered settings has revealed co-existence of microorganisms from all domains of life, including Bacteria, Archaea and Eukarya. The coexistence of these dynamic microbes is not arbitrary, as a highly coordinated architectural setup and physiological complexity show ecological interdependence and myriads of underlying interactions. In this review, we describe how species from different kingdoms interact in biofilms and discuss the functional consequences of such interactions. We highlight metabolic advances of collaboration among species from different kingdoms, and advocate that these interactions are of great importance and need to be addressed in future research. Since trans-kingdom biofilms impact diverse contexts, ranging from complicated infections to efficient growth of plants, future knowledge within this field will be beneficial for medical microbiology, biotechnology, and our general understanding of microbial life in nature.

Anthropogenic Intensity-Determined Assembly and Network Stability of Bacterioplankton Communities in the Le'an River

Bacterioplankton are essential components of riverine ecosystems. However, the mechanisms (deterministic or stochastic processes) and co-occurrence networks by which these communities respond to anthropogenic disturbances are not well understood. Here, we integrated niche-neutrality dynamic balancing and co-occurrence network analysis to investigate the dispersal dynamics of bacterioplankton communities along human activity intensity gradients. Results showed that the lower reaches (where intensity of human activity is high) had an increased composition of bacterioplankton communities which induced strong increases in bacterioplankton diversity. Human activity intensity changes influenced bacterioplankton community assembly via regulation of the deterministic-stochastic balance, with deterministic processes more important as human activity increases. Bacterioplankton molecular ecological network stability and robustness were higher on average in the upper reaches (where there is lower intensity of human activity), but a human activity intensity increase of about 10%/10% can reduce co-occurrence network stability of bacterioplankton communities by an average of 0.62%/0.42% in the dry and wet season, respectively. In addition, water chemistry (especially NO₃^–-N and Cl^–) contributed more to explaining community assembly (especially the composition) than geographic distance and land use in the dry season, while the bacterioplankton community (especially the bacterioplankton network) was more influenced by distance (especially the length of rivers and dendritic streams) and land use (especially forest regions) in the wet season. Our research provides a new perspective of community assembly in rivers and important insights into future research on environmental monitoring and classified management of aquatic ecosystems under the influence of human activity.

Eutrophication decrease compositional dissimilarity in freshwater plankton communities

Human activities, such as land use change and eutrophication, threaten freshwater biodiversity and ecosystem function. In this study, we examined both the α- and β-diversity of plankton communities, that is, bacteria/prokaryotic algae, eukaryotic algae, and zooplankton/metazoans, using both classical microscopy and high-throughput sequencing methods across 40 lakes of the Yangtze River Basin. The spatial variations in plankton communities were explained by environmental variables such as trophic status index (TSI) and environmental heterogeneity according to non-metric multidimensional scaling analyses, mantel tests, and structural equation model. Our results showed that the compositional dissimilarities of bacteria, cyanobacteria, eukaryotic algae, and metazoans all decreased with the increasing TSI values, and were significantly positively related to environmental dissimilarity. Both the species richness and compositional dissimilarity of zooplankton had positive effects on zooplankton/phytoplankton biomass ratio. Zooplankton diversity was not directly affected by TSI and environmental dissimilarity; however, it was indirectly affected by the biotic interactions with cyanobacteria or eukaryotic algae. In addition, there were significant positive relationships between bacteria/cyanobacteria and eukaryotic algae dissimilarities. Our results indicated that increased trophic status and decreased environmental dissimilarity as consequences of eutrophication may weaken the trophic cascading effects of planktonic food chain via reducing the top-down effects of zooplankton on phytoplankton.

Exploring microbial diversity and ecological function of epiphytic and surface sediment biofilm communities in a shallow tropical lake

Microbial communities in epiphytic biofilms and surface sediments play a vital role in the biogeochemical cycles of the major chemical elements in freshwater. However, little is known about the diversity, composition, and ecological functions of microbial communities in shallow tropical lakes dominated by aquatic macrophytes. In this study, epiphytic bacterial and eukaryotic biofilm communities on submerged and floating macrophytes and surface sediments were investigated in Lake Rumira, Rwanda in August and November 2019. High-throughput sequencing data revealed that members of the phyla, including Firmicutes, Proteobacteria, Cyanobacteria, Actinobacteria, Chloroflexi, Bacteriodetes, Verrumicrobia, and Myxomycota, dominated bacterial communities, while the microeukaryotic communities were dominated by Unclassified (uncl) SAR(Stramenopiles, Alveolata, Rhizaria), Rotifers, Ascomycota, Gastrotricha, Platyhelminthes, Chloroplastida, and Arthropoda. Interestingly, the eukaryotic OTUs (operational taxonomic units) number and Shannon indices were significantly higher in sediments and epiphytic biofilms on Eicchornia crassipes than Ceratophyllum demersum (p < 0.05), while no differences were observed in bacterial OTUs number and Shannon values among substrates. Redundancy analysis (RDA) showed that water temperature, pH, dissolved oxygen (DO), total nitrogen (TN), and electrical conductivity (EC) were the most important abiotic factors closely related to the microbial community on C. demersum and E. crassipes. Furthermore, co-occurrence networks analysis (|r| > 0.7, p < 0.05) and functional prediction revealed more complex interactions among microbes on C. demersum than on E. crassipes and sediments, and those interactions include cross-feeding, parasitism, symbiosis, and predatism among organisms in biofilms. These results suggested that substrate-type and environmental factors were the strong driving forces of microbial diversity in epiphytic biofilms and surface sediments, thus shedding new insights into microbial community diversity in epiphytic biofilms and surface sediments and its ecological role in tropical lacustrine ecosystems.

Effects of biofilm on metal adsorption behavior and microbial community of microplastics

In this study, the adsorption behavior of Cu(II) and Pb(II) on the biofilm-developed polystyrene (PS) microplastics (MPs) was compared with the virgin PS (V-PS) and UV-aged PS (UV-PS). The results demonstrated that the biofilm could enhance the adsorption abilities onto MPs more than UV radiation. The intra-particle diffusion model suggested that the adsorption on V-PS was dominated by intra-particle diffusion, while the adsorption rate was controlled by the binding diffusion on UV-PS and biofilm-developed PS (Bio-PS). Compared with the V-PS and UV-PS, the Bio-PS showed the largest adsorption capacity based on the Freundlich isotherm model, which indicated that the adsorption of heavy metals onto Bio-PS was multilayer and heterogeneous. The adsorption mechanism of Bio-PS contained physical adsorption, chemisorption, and biosorption. These Bio-PS adsorption types participated in both oxygen and nitrogen groups. Based on the 16S rRNA analysis, the diversity of the microbial community with biofilm changed to a certain extent after the adsorption of heavy metals. Furthermore, the stress of lead (Pb) adsorption had a higher impact on the microbial community distribution and the PS biofilm. This study illustrated how the formation of biofilms can highly affect the adsorption behavior of MPs as well as the microbial community of MPs.

Diel metabolism of Yellow Sea green tide algae alters bacterial community composition under in situ seawater acidification of coastal areas

Ocean acidification in coastal seawaters is a complex process, with coastal pH being affected by numerous factors including watershed and biological processes that also support metabolically diverse bacterial communities. The world's largest macroalgal blooms have occurred consecutively in the Yellow Sea over the last 13 years. In particular, algal mats formed by Yellow Sea green tides (YSGT) significantly influence coastal environments. Herein, we hypothesized that 1) inorganic carbonate chemistry in coastal areas is altered by diel metabolism of these giant algal mats and that 2) bacterial community composition in diffusive boundary layers might be altered along diel cycles due to algal mat metabolism. In situ studies indicated that algal mat metabolism led to changes in diel pH and CO₂ in affected seawaters. Such metabolic activities could intensify diel pH fluctuations in algal mat diffusive boundary layers, as noted by pH fluctuations of 0.22 ± 0.01 units, and pCO₂ fluctuations of 214.62 ± 29.37 μatm per day. In contrast, pH fluctuations of 0.11 ± 0.02 units and pCO₂ fluctuations of 79.02 ± 42.70 μatm were noted in unaffected areas. Furthermore, the bacterial community composition associated with diffusive algal boundary layers, including those of ambient bacteria and epiphytic bacteria, exhibited diel changes, while endophytic bacterial communities were relatively stable. Flavobacteriaceae were particularly highly abundant taxa in the ambient and epiphytic bacterial communities and exhibited increased abundances at night but sharp decreases in abundances during daytime. Flavobacteriaceae are heterotrophic taxa that could contribute to coastal area acidification at night due to the transformation of organic carbon to inorganic carbon. These results provide new insights to understand the variability in coastal ocean acidification via harmful algal blooms while providing a framework for evaluating the effects of YSGT on costal carbon cycling.

Significant impact of seasonality, verticality and biofilm on element accumulation of aquatic macrophytes

Submersed macrophytes accumulate large amounts of macro- and trace elements from the environment and, therefore, are frequently used as indicators of water pollution and tools to remove pollutants from contaminated waters. This study provides evidences that the quantity of macro- and trace elements accumulated in the macrophyte Ceratophyllum demersum depends strongly on the seasonality, on the vertical position of the plant material and on the biofilm cover. Element contents of macrophytes with and without biofilm cover and that of vertical plant sections were investigated by an ICP-MS technique in three different habitats, at the beginning and at the end of the vegetation period. Results demonstrated that the element concentrations of Ceratophyllum demersum dropped to one-half and one-eighth by the end of the summer; and the amount of certain elements in the lower part of plants were up to six times higher than in the upper and in plants with well-developed epiphytic microbial community 2-5-fold higher than in plants without biofilm. These results help in phytoremediation practice and in setting up future biomonitoring studies. When it is necessary to calculate the exact amount of elements which can be accumulated by plants in a polluted environment or should be removed from a contaminated water by harvesting macrophytes, it is of high importance to consider the month of the study, the plant parts harvested and the biofilm cover.

Response of sediment and water microbial communities to submerged vegetations restoration in a shallow eutrophic lake

Submerged macrophytes are the main primary producers in shallow lakes and play an important role in structuring communities. Aquatic microbes are also an important component of aquatic ecosystems and play important roles in maintaining the health and stability of ecosystems. However, little is known about the interactions between macrophytes and microbes during the reintroduction of submerged vegetation. Here, we chose restored zones dominated by four different submerged vegetations and a bare zone in a shallow eutrophic lake to unveil the microbial diversity, composition and structure changes in sediment and water samples after submerged macrophytes were recovered for one and a half years (July 2019) and two years (April 2020). We found that the recovery of submerged vegetations decreased phosphorus content in water and sediments but increased nitrogen and carbon content in sediments. We observed that the transparency of water in the restored zones was significantly higher than that in the bare zone in July. The recovery of submerged vegetations significantly influenced the alpha diversity of bacterial communities in sediments, with higher values observed in restored zones than in bare zones, whereas no significant influence was found in the water samples. In July, the macrophyte species showed strong effects on the bacterial community composition in water and relatively little effect in sediment. However, a strong effect of the macrophyte species on the composition of bacterial communities in sediments was observed in April, which may be related to the decomposition of plant litter and the decay of detritus. Additionally, the dissimilarity of the sedimentary bacterial community may increase more slowly with environmental changes than the planktonic bacterial community dissimilarity. These results suggest that the large-scale restoration of aquatic macrophytes can not only improve water quality and change sediment characteristics but can also affect the diversity and compositions of bacterial communities, and these effects seem to be very long-lasting.

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.

Spatial and Temporal Distribution of Bacterioplankton Molecular Ecological Networks in the Yuan River under Different Human Activity Intensity

Bacterioplankton communities play a crucial role in freshwater ecosystem functioning, but it is unknown how co-occurrence networks within these communities respond to human activity disturbances. This represents an important knowledge gap because changes in microbial networks could have implications for their functionality and vulnerability to future disturbances. Here, we compare the spatiotemporal and biogeographical patterns of bacterioplankton molecular ecological networks using high-throughput sequencing of Illumina HiSeq and multivariate statistical analyses from a subtropical river during wet and dry seasons. Results demonstrated that the lower reaches (high human activity intensity) network had less of an average degree (10.568/18.363), especially during the dry season, when compared with the upper reaches (low human activity intensity) network (10.685/37.552) during the wet and dry seasons, respectively. The latter formed more complexity networks with more modularity (0.622/0.556) than the lower reaches (high human activity intensity) network (0.505/0.41) during the wet and dry seasons, respectively. Bacterioplankton molecular ecological network under high human activity intensity became significantly less robust, which is mainly caused by altering of the environmental conditions and keystone species. Human activity altered the composition of modules but preserved their ecological roles in the network and environmental factors (dissolved organic carbon, temperature, arsenic, oxidation-reduction potential and Chao1 index) were the best parameters for explaining the variations in bacterioplankton molecular ecological network structure and modules. Proteobacteria, Actinobacteria and Bacteroidetes were the keystone phylum in shaping the structure and niche differentiations in the network. In addition, the lower reaches (high human activity intensity) reduce the bacterioplankton diversity and ecological niche differentiation, which deterministic processes become more important with increased farmland and constructed land area (especially farmland) with only 35% and 40% of the community variation explained by the neutral community model during the wet season and dry season, respectively. Keystone species in high human activity intensity stress habitats yield intense functional potentials and Bacterioplankton communities harbor keystone taxa in different human activity intensity stress habitats, which may exert their influence on microbiome network composition regardless of abundance. Therefore, human activity plays a crucial role in shaping the structure and function of bacterioplankton molecular ecological networks in subtropical rivers and understanding the mechanisms of this process can provide important information about human-water interaction processes, sustainable uses of freshwater as well as watershed management and conservation.

Temporal Changes of the Epiphytic Bacteria Community From the Marine Macroalga Ulva lactuca (Santa Marta, Colombian-Caribbean)

Microbial communities live on macroalgal surfaces. The identity and abundance of the bacteria making these epiphytic communities depend on the macroalgal host and the environmental conditions. Macroalgae rely on epiphytic bacteria for basic functions (spore settlement, morphogenesis, growth, and protection against pathogens). However, these marine bacterial-macroalgal associations are still poorly understood for macroalgae inhabiting the Colombian Caribbean. This study aimed at characterizing the epiphytic bacterial community from macroalgae of the species Ulva lactuca growing in La Punta de la Loma (Santa Marta, Colombia). We conducted a 16S rRNA gene sequencing-based study of these microbial communities sampled twice a year between 2014 and 2016. Within these communities, the Proteobacteria, Bacterioidetes, Cyanobacteria, Deinococcus-Thermus and Actinobacteria were the most abundant phyla. At low taxonomic levels, we found high variability among epiphytic bacteria from U. lactuca and bacterial communities associated with macroalgae from Germany and Australia. We observed differences in the bacterial community composition across years driven by abundance shifts of Rhodobacteraceae Hyphomonadaceae, and Flavobacteriaceae, probably caused by an increase of seawater temperature. Our results support the need for functional studies of the microbiota associated with U. lactuca, a common macroalga in the Colombian Caribbean Sea.