Planktonic Bacterial Communities Research Articles

Biogeography of Planktonic and Benthic Bacterial Communities of Lake Khubsugul (Mongolia)

Biogeography of Planktonic and Benthic Bacterial Communities of Lake Khubsugul (Mongolia)

Distinct Assembly Processes Structure Planktonic Bacterial Communities Among Near- and Offshore Ecosystems in the Yangtze River Estuary

The estuarine system functions as natural filters due to its ability to facilitate material transformation, planktonic bacteria play a crucial role in the cycling of complex nutrients and pollutants within estuaries, and understanding the community composition and assembly therein is crucial for comprehending bacterial ecology within estuaries. Despite extensive investigations into the composition and community assembly of two bacterial fractions (free-living, FLB; particle-attached, PAB), the process by which bacterioplankton communities in these two habitats assemble in the nearshore and offshore zones of estuarine ecosystems remains poorly understood. In this study, we conducted sampling in the Yangtze River Estuary (YRE) to investigate potential variations in the composition and community assembly of FLB and PAB in nearshore and offshore regions. We collected 90 samples of surface, middle, and bottom water from 16 sampling stations and performed 16S rRNA gene amplicon analysis along with environmental factor measurements. The results unveiled that the nearshore communities demonstrated significantly greater species richness and Chao1 indices compared to the offshore communities. In contrast, the nearshore communities had lower values of Shannon and Simpson indices. When compared to the FLB, the PAB exhibit a higher level of biodiversity and abundance. However, no distinct alpha and beta diversity differences were observed between the bottom, middle, and surface water layers. The community assembly analysis indicated that nearshore communities are predominantly shaped by deterministic processes, particularly due to heterogeneous selection of PAB; In contrast, offshore communities are governed more by stochastic processes, largely due to homogenizing dispersal of FLB. Consequently, the findings of this study demonstrate that nearshore and PAB communities exhibit higher levels of species diversity, while stochastic and deterministic processes exert distinct influences on communities among near- and offshore regions. This study further sheds new light on our understanding of the mechanisms governing bacterial communities in estuarine ecosystems.

Differences of bacterioplankton communities between the source and upstream regions of the Yangtze River: microbial structure, co-occurrence pattern, and environmental influencing factors.

The source area of the Yangtze River is located in the hinterland of the Qinghai-Tibet Plateau, which is known as the "Earth's third pole." It is the water conservation area and the natural barrier of the ecosystem of the Yangtze River basin. It is also the most sensitive area of the natural ecosystem, and the ecological environment is very fragile. Microorganisms play key roles in the biogeochemical processes of water. In this paper, the bacterioplankton communities in the source and upstream regions of the Yangtze River were studied based on 16S rRNA high-throughput sequencing, and their environmental influencing factors were further analyzed. Results showed that the upstream region had higher richness and diversity than the source region. The predominant bacterial phyla in the source and upstream regions were Proteobacteria, Firmicutes, and Actinobacteriota. The bacterial phyla associated with municipal pollution and opportunistic pathogen, such as Firmicutes and Actinobacteriota, were more abundant in the upstream. By contrast, distinct planktonic bacterial genera associated with mining pollution, such as Acidiphilium and Acidithiobacillus, were more abundant in the source region. The co-occurrence network showed that the interaction of bacterioplankton community is more frequent in the upstream. The bacterioplankton community compositions, richness, and functional profiles were affected by the spatial heterogeneity. Moreover, variation partitioning analysis further confirmed that the amount of variation in the source region independently explained by variables of altitude was the largest, followed by water nutrient. This paper revealed the spatial distribution of planktonic bacterial communities in the source and upstream regions of the Yangtze River and its correlation with environmental factors, providing information support for ensuring the health and safety of aquatic ecosystems in the Yangtze River Basin.

Deciphering variations in the surficial bacterial compositions and functional profiles in the intersection between North and South Yellow Sea

The coastal ocean systems play paramount role in the nutrient biogeochemistry because of its interconnected environment. To gain a novel insight into coupling relationships between bacterial community, functioning properties and nutrient metabolism, we conducted analysis on the patterns and driving factors of planktonic bacterial functional community across subsurface water of marine ranching near the Yellow Sea in both summer and winter. Illumina HiSeq Sequencing and a corresponding set of biogeochemical data were used to assess distribution patterns of taxa, adaptive mechanism and metabolic function. Results demonstrated that Proteobacteria, Cyanobacteria, Actinobacteriota and Bacteroidota were dominant phyla both in summer and winter. Taxonomic profiles related to nutrient variation were found to be highly correlated with Dissolved Oxygen (DO) and Chlorophyll fluorescence (FLUO), and distinct diversity differences were also found between summer and winter samples. Functional activity in summer associated with the relative abundance of phototrophy and photoautotrophy were the highest in the subsurface water, while in winter the dominant functional properties were mainly include chemoheterotrophy and aerobic_ chemoheterotrophy. A significant difference related to functional activity between summer and winter, mainly representing ligninolysis and iron_respiration. In general, our study provides a framework for understanding the relative importance of environmental factors, temperature variation and nutrient availability in shaping the metabolic processes of aquatic microorganisms, particularly in ocean mariculture systems.

Marine resistome of a temperate zone: Distribution, diversity, and driving factors across the trophic gradient

Marine and ocean environments are the most widespread habitats in the world but are still the least studied from the aspect of antibiotic resistance. The indigenous and tetracycline (TET)- and sulfamethoxazole (SXT)-resistant planktonic bacterial communities were simultaneously investigated for the first time along a trophic gradient of a temperate zone, regarding their taxonomic and functional structures as well as biotic and abiotic factors affecting their dynamics as vehicles of antibiotic resistance genes (ARGs), thus impacting the ARGs distribution at seasonal and spatial scales.A total of 80 microbiomes, recovered seasonally from bottom layer and surface waters along a 68-km transect from wastewater-impacted estuary to coastal and pristine open sea in the central Adriatic (Mediterranean Sea), were analysed using 16S rRNA amplicon sequencing, PICRUSt2 bioinformatics and extensive biostatistics. Eighty-one bacterial phyla were identified, with majority (n = 49) in summer when communities were found to be more species enriched across the gradient. Microbial diversity was more site-specific and pronounced in surface microbiomes in winter. Nevertheless, both richness and community diversity decreased with distance from the coast. Although the microbiomes from human-influenced sites significantly differed from those in oligotrophic offshore area, Proteobacteria were still the most abundant phylum during both seasons at the surface and seabed along the gradient, and the major contributors to the marine resistome regarding native and TET- and SXT-resistant microbial communities. Resistome structure was more diverse in winter, whereas peptide, vancomycin and multidrug resistance modules predominated regardless of season, trophic status, or antibiotic. However, multidrug, beta-lactam resistance modules as well as macrolide, phenicol, aminoglycoside, and particularly imipenem resistance genes were much more frequent in winter, suggesting that the diversity of indigenous resistomes is highly dependent on seasonal variations of the water column, driven by thermohaline stratification and nutrients. Moreover, several pathogenic genera stood out as important carriers of multiple resistance traits in TET- and SXT-related resistomes in both seasons, particularly Acinetobacter, Vibrio, Bacillus and Pseudomonas, beside which Proteus, Serratia and Bacteroides prevailed in native resistomes.This study evidenced seasonal and spatial variations of the marine microbiome and resistome and their driving forces along the trophic gradient, providing a comprehensive insight into the diversity and distribution of antibiotic resistance in the marine ecosystem of a temperate zone.

Planktonic archaea reveal stronger dispersal limitation and more network connectivity than planktonic bacteria in the Jinsha River of southwestern China

Abstract Planktonic archaea and bacteria play important roles in biogeochemical cycling, but their biogeographical patterns and underlying ecological processes remain poorly understood, particularly in large‐scale rivers. We collected 43 water samples covering a 2279 km reach of the Jinsha River, one of the largest rivers in southwest China, and performed high‐throughput sequencing analysis on planktonic archaeal and bacterial communities. Partial Mantel analysis and neutral model were used to assess the factors influencing microbial distributions. The associations among different microbial species and their geographical distribution patterns were linked through co‐occurrence networks, and the putative key taxa in the archaeal and bacterial networks were analysed. The Shannon index of both archaeal and bacterial communities was highest in the midstream reach. The Pielou's evenness of archaea did not vary among the three reaches, whereas those of bacteria increased from upstream to downstream. The archaeal and bacterial community compositions were significantly different in the three reaches, but the differences among the bacterial communities were greater than among the archaeal communities. Both dispersal limitation and environmental selection affected the community compositions of the archaea and bacteria, but dispersal limitation was the most influential factor. Compared to archaea, bacteria were less affected by dispersal limitation and more by environmental selection. The co‐occurrence network analysis demonstrated that, compared with the bacterial network of all sites, the archaeal network with larger graph density had higher connectivity and complexity, but a lower proportion of negative correlations. The putative key taxa belonged to Nitrososphaeraceae and Candidatus_Nitrocosmicus from the archaeal community, and Hydrogenophaga and Sphingorhabdus from the bacterial community. Taken together, these findings demonstrated that the planktonic archaea were more dispersal‐limited and showed more network connectivity than the planktonic bacteria in the Jinsha River. This study enhances our understanding of the biogeographical distribution patterns and underlying ecological processes of planktonic microorganisms over large‐scale freshwater systems.

Salinization and sedimentation drive contrasting assembly mechanisms of planktonic and sediment-bound bacterial communities in agricultural streams.

Agriculture is the most dominant land use globally and is projected to increase in the future to support a growing human population but also threatens ecosystem structure and services. Bacteria mediate numerous biogeochemical pathways within ecosystems. Therefore, identifying linkages between stressors associated with agricultural land use and responses of bacterial diversity is an important step in understanding and improving resource management. Here, we use the Mississippi Alluvial Plain (MAP) ecoregion, a highly modified agroecosystem, as a case study to better understand agriculturally associated drivers of stream bacterial diversity and assembly mechanisms. In the MAP, we found that planktonic bacterial communities were strongly influenced by salinity. Tolerant taxa increased with increasing ion concentrations, likely driving homogenous selection which accounted for ~90% of assembly processes. Sediment bacterial phylogenetic diversity increased with increasing agricultural land use and was influenced by sediment particle size, with assembly mechanisms shifting from homogenous to variable selection as differences in median particle size increased. Within individual streams, sediment heterogeneity was correlated with bacterial diversity and a subsidy-stress relationship along the particle size gradient was observed. Planktonic and sediment communities within the same stream also diverged as sediment particle size decreased. Nutrients including carbon, nitrogen, and phosphorus, which tend to be elevated in agroecosystems, were also associated with detectable shifts in bacterial community structure. Collectively, our results establish that two understudied variables, salinity and sediment texture, are the primary drivers of bacterial diversity within the studied agroecosystem, whereas nutrients are secondary drivers. Although numerous macrobiological communities respond negatively, we observed increasing bacterial diversity in response to agricultural stressors including salinization and sedimentation. Elevated taxonomic and phylogenetic bacterial diversity likely increases the probability of detecting community responses to stressors. Thus, bacteria community responses may be more reliable for establishing water quality goals within highly modified agroecosystems that have experienced shifting baselines.

Comparative microbiota characterization unveiled a contrasting pattern of floc-associated versus free-living bacterial communities in biofloc aquaculture

Bacterial communities thriving in various components determine the host health and water quality in biofloc technology (BFT)-based aquaculture system. Despite increasing utilization of BFT in aquaculture industries, studies distinguishing bioflocs (attached community) and rearing water (free-living community) microbiota compositions remain rudimentary. In this study, we compared floc-associated bacterial (FAB; size fraction ≥3 μm) and planktonic free-living bacterial (PFLB; 0.22–3.00 μm) communities from a commercial shrimp aquaculture system to investigate how their diversity, community compositions, inter-species interactions, and functional potentials varied. Based on 16S rRNA gene amplicon sequencing, the metataxonomic results indicated that though these communities share identical habitat, the FAB community possesses a higher bacterial richness and noticeably distinct community composition than its PFLB counterpart. The Alphaproteobacteria (mostly Rhodobacteraceae) preponderated in the FAB community, while Bacteroidetes (primarily Flavobacteriaceae) dominated the PFLB. By analyzing co-occurrence pattern, we portrayed a complex ecological network, strong inter-species interactions, and diverse keystone taxa in the FAB community. Intriguingly, Halieaceae and Rhodobacteraceae members were recognized as prominent keystone taxa in FAB and PFLB communities, respectively, highlighting their regulatory roles in sustaining stability of these communities. Furthermore, negative edges proportion varied considerably in ecological networks, suggesting that both communities experience distinct niche differentiation. PICRUSt2-based prediction demonstrated that functional pathways pertaining to membrane transporters, cell motility, and polymer degradation were enriched in the FAB community, suggesting their involvement in surface-adapted lifestyles. Altogether, we proved that attached and planktonic bacterial communities serve as two distinct microbial consortia, perform different tasks, and hence could have diverse ecological roles in biofloc aquaculture systems. Our findings advance scientific understanding of microbiota variations between planktonic and attached communities in aquatic environments, and strengthen the proposed species sorting hypothesis, which states that prevailing environmental factors determine bacterial community assembly.

Habitat-specific regulation of bacterial community dynamics during phytoplankton bloom succession in a subtropical eutrophic lake

Phytoplankton blooms, an important indicator of severe eutrophication, are a globally significant consequence of anthropogenic activities and climate change on freshwater lakes. Shifts in microbial communities during phytoplankton blooms have been extensively investigated, yet we have a limited understanding of how distinct assembly processes underlying the temporal dynamics of freshwater bacterial communities within different habitats respond to the succession of phytoplankton blooms. To address this knowledge gap, we collected both water and sediment samples in a subtropical eutrophic lake over a complete period of phytoplankton blooms to assess the dynamics of bacterial communities and the temporal shifts in assembly processes. Our results showed that phytoplankton blooms strongly altered the diversity, composition, and coexistence patterns of both planktonic and sediment bacterial communities (PBC and SBC), but the successional patterns differed between PBC and SBC. PBC were less temporally stable under bloom-induce disturbances, with higher variations in temporal dynamics and greater sensitivity to environmental fluctuations. Furthermore, the temporal assembly patterns of bacterial communities in both habitats were mainly driven by homogeneous selection and ecological drift. In the PBC, the role of selection decreased over time, while ecological drift became increasingly important. Conversely, in the SBC, the relative impact of selection and ecological drift on community assemblages fluctuated less over time, with selection remaining the dominant process throughout the bloom.

The different responses of planktonic bacteria and archaea to water temperature maintain the stability of their community diversity in dammed rivers

BackgroundPlanktonic bacteria and archaea play a key role in river nutrient biogeochemical cycling; however, their respective community assembly and how to maintain their diversity are not well known in dammed rivers. Therefore, a seasonal survey of planktonic bacterial and archaeal community compositions and related environmental factors was conducted in 16 cascade reservoirs and corresponding river waters on the Wujiang River and the Pearl River in southwest China to understand the above mechanisms.ResultsDeterministic processes dominated bacterial and archaeal community assembly. The structural equation models showed that water temperature can directly or indirectly affect the microbial diversity. Interestingly, planktonic bacterial diversity increased with increasing water temperature, while archaea showed the opposite trend; the overall diversity of bacteria and archaea was no significant changes with changeable water temperature. Abundant microbes had a stronger distance–decay relationship than middle and rare ones, and the relationship was stronger in winter and spring than in summer and autumn.ConclusionsPlanktonic bacteria and archaea in dammed rivers had different biogeographic distributions, and water temperature was a key controlling factor. The different responses of planktonic bacterial and archaeal diversity to water temperature could be due to their different phylogenetic diversity. This ultimately maintained the stability of total microbial community diversity. This study reveals the different responses of planktonic bacteria and archaea to water temperature and perfects the theoretical framework for planktonic microbial biogeography in dammed rivers.

Variations in seaweed-associated and planktonic bacterial communities along the coast of Ghana

ABSTRACT Seaweed associated bacteria can be exploited for sustainable production and conservation of seaweeds, although limited information exists in several coastal waters in West Africa. Here, the diversity and abundance of bacteria on five seaweeds, Sargassum vulgare, Padina durvillaei, Hydropuntia dentata, Hypnea musciformis and Ulva fasciata, and surrounding seawaters across five coastal sites in the Central and Western regions of Ghana were investigated. Biochemical tests and MALDI–TOF identification system were used to determine the bacteria diversity and abundance on the seaweeds and seawater. A total of 530 bacterial isolates, belonging to 28 species (and mostly Proteobacteria and Firmicutes) were identified. A higher diversity of bacteria species was found associated with the seaweeds (83%) than in seawater (17%). Bacterial composition was similar among taxonomically-related seaweeds. The brown (S. vulgare) and red (H. musciformis) seaweeds recorded the most and least diverse bacterial assemblage, respectively. Seasonally, bacterial diversity and abundance were marginally higher in the wet season. The study provides important baseline information on the spatial, temporal and taxonomic distribution of bacteria associated with commercially valuable seaweed species in the coastal areas of Ghana. The results are also important for the sustainable exploitation and conservation of these important macroalgae in Ghana and elsewhere.

Metagenomic profiles of planktonic bacteria and resistome along a salinity gradient in the Pearl River Estuary, South China

Estuarine ecosystems undergo pronounced and intricate changes due to the mixing of freshwater and saltwater. Additionally, urbanization and population growth in estuarine regions result in shifts in the planktonic bacterial community and the accumulation of antibiotic resistance genes (ARGs). The dynamic changes in bacterial communities, environmental factors, and carriage of ARGs from freshwater to seawater, as well as the complex interrelationships among these factors, have yet to be fully elucidated. Here, we conducted a comprehensive study based on metagenomic sequencing and full-length 16S rRNA sequencing, covering the entire Pearl River Estuary (PRE) in Guangdong, China. The abundance and distribution of the bacterial community, ARGs, mobile genetic elements (MGEs), and bacterial virulence factors (VFs) were analyzed on a site-by-site basis through sampling along the salinity gradient in PRE, from upstream to downstream. The structure of the planktonic bacterial community undergoes continuous changes in response to variations in estuarine salinity, with the phyla Proteobacteria and Cyanobacteria being dominant bacterial throughout the entire region. The diversity and abundance of ARGs and MGEs gradually decreased with the direction of water flow. A large number of ARGs were carried by potentially pathogenic bacteria, especially in Alpha-proteobacteria and Beta-proteobacteria. Multi-drug resistance genes have the highest abundance and subtypes in PRE. In addition, ARGs are more linked to some MGEs than to specific bacterial taxa and disseminate mainly by HGT and not by vertical transfer in the bacterial communities. Various environmental factors, such as salinity and nutrient concentrations, have a significantly impact on the community structure and distribution of bacteria. In conclusion, our results represent a valuable resource for further investigating the intricate interplay between environmental factors and anthropogenic disturbances on bacterial community dynamics. Moreover, they contribute to a better understanding of the relative impact of these factors on the dissemination of ARGs.

The Impact of IMTA on the Spatial and Temporal Distribution of the Surface Planktonic Bacteria Community in the Surrounding Sea Area of Xiasanhengshan Island of the East China Sea

The growing world population has produced an increasing demand for seafood, and the aquaculture industry is under corresponding pressure to fill this demand. The offshore ecology and environment are under significant threat with the continuous expansion of the scale and intensity of aquaculture. Integrated multi-tropic aquaculture (IMTA) is a healthy and sustainable mariculture model based on ecosystem-level management, and has become popular in recent years. It is an effective way to cope with the significant changes in offshore ecosystems under multiple stressors. Phytoplankton bacteria are essential to maintaining the marine ecosystem’s balance and stability. Investigating the changes in the community structure of marine planktonic bacteria can elucidate the impact of mariculture on the marine ecological environment. This study took the fish-shell IMTA system with natural macroalgae nearby as the object, and monitored the plankton community’s structure in the system’s surface seawater for four quarters from July 2020 to April 2021. The space–time distribution characteristics and influencing factors of the plankton community in the surface water were examined. The results showed no significant difference between the planktonic bacterial communities at different sampling sites. There was also no significant difference in the α-diversity index. However, the dominant species and abundance of planktonic bacteria at the sampling sites differed significantly. Proteobacteria and Bacteroides were the dominant groups of planktonic bacteria. The results of the distance-based redundancy analysis demonstrated that chemical oxygen demand, chlorophyll a, and dissolved oxygen constituted the primary environmental factors affecting the planktonic bacterial community structures. The heatmap also showed that NH4+- N, temperature, and salinity levels were also related to certain planktonic bacteria. This study preliminarily identified the distribution of the surface bacterial plankton community and its response to changes in environmental factors in the sea area near Xiasanhengshan Island. The results provide a preliminary basis for assessing the health and stability of the IMTA system in open sea areas.

Nitrogen and Phosphorus Discriminate the Assembly Processes of Prokaryotic and Eukaryotic Algae in an Agricultural Drainage Receiving Lake

Phytoplankton and bacteria play key roles in material cycling and their consequent eco-functions in lakes, which are threatened by anthropogenic pressures, especially agricultural activities, which, in the watershed, are effective in changing the material composition and hydrodynamic conditions of the lake through material input and water withdrawal. This process theoretically changes the interaction and assembly pattern of microorganisms, which are important factors driving the structural and functional evolution of ecological communities in lakes. In this research, the community structure, interactions, and assembly of phytoplankton and bacteria were investigated during agro-irrigation seasons in a typical agricultural drainage receiving lake, Wuliangsuhai. The results showed that the seasonal variations in the community were driven by nitrogen and phosphorus. In particular, Cyanobacteria increased significantly during the seasons with the regulation of TP (λ = 0.56, p < 0.01, n = 30). The TN positively drove Chlorophyta and Bacillariophyta (λ = 0.42 and 0.65, p < 0.05, n = 30). Furthermore, MENA showed that planktonic algae and bacterial community interactions were enhanced, and interspecific competition increased at high trophic levels. The community assembly is primarily a stochastic process that is mostly related to hydrodynamic conditions. The second related factor, nitrogen and phosphorus inputs, had obvious effects on community assembly, which responded to its effects on species diversity, niche width, and interactions, and they jointly controlled community assembly. This study reveals that the assembly processes of bacteria and planktonic algae were driven by different environmental factors in specific ways, which provides a new view for understanding agriculture’s impacts on microecology and helps in developing lake protection strategies.

Responses of Free-Living Planktonic Bacterial Communities to Experimental Acidification and Warming

Climate change driven by human activities encompasses the increase in atmospheric CO2 concentration and sea-surface temperature. Little is known regarding the synergistic effects of these phenomena on bacterial communities in oligotrophic marine ecosystems that are expected to be particularly vulnerable. Here, we studied bacterial community composition changes based on 16S rRNA sequencing at two fractions (0.1-0.2 and >0.2 μm) during a 10- day fully factorial mesocosm experiment in the eastern Mediterranean where the pH decreased by ~0.3 units and temperature increased by ~3 °C to project possible future changes in surface waters. The bacterial community experienced significant taxonomic differences driven by the combined effect of time and treatment; a community shift one day after the manipulations was noticed, followed by a similar state between all mesocosms at the third day, and mild shifts later on, which were remarkable mainly under sole acidification. The abundance of Synechococcus increased in response to warming, while the SAR11 clade immediately benefited from the combined acidification and warming. The effect of the acidification itself had a more persistent impact on community composition. This study highlights the importance of studying climate change consequences on ecosystem functioning both separately and simultaneously, considering the ambient environmental parameters.

Diversity Patterns and Influencing Factors of Epibiotic in Vallisneria natans and Planktonic Bacteria Communities

Planktonic and epiphytic bacterial communities play an important role in wetland nitrogen pollutant removal and water purification, yet their community dynamics are far from understood compared with those of the wetland soil bacterial community. Taking the planktonic bacterial community in the Yuguqiao constructed wetland and the epiphytic bacterial community on the leaf surface of the common submerged plant Vallisneria natans as the research objects, the composition, structure, and functional diversity of planktonic and epiphytic bacterial communities were analyzed using high-throughput sequencing. The results showed that the compositions of the planktonic and epiphytic bacterial communities were significantly different, with more heterotrophic and denitrifying bacteria present in the epiphytic bacterial community than in the planktonic bacterial community. The α diversity of the planktonic bacterial community was significantly different among the three sampling sites but not in the epiphytic bacterial community. In general, the OTU index and Shannon index of the epiphytic bacterial community were significantly higher than those of the planktonic bacterial community, and they had obvious spatial heterogeneity. RDA analysis showed that DO, IC, TP, NH+4, and TOC had important effects on the structural changes of both planktonic and epiphytic bacterial communities but had a greater impact on planktonic bacterial communities. Co-occurrence network analysis showed that the epiphytic bacterial community had more niche differentiation, a more stable network, and stronger resistance to external disturbance. The results of FAPROTAX functional prediction analysis showed that the nitrogen cycling, especially denitrification of the epiphytic bacterial community, was significantly greater than that of the planktonic bacterial community. The results of this study revealed the driving mechanism for maintaining the diversity of planktonic and epiphytic bacterial communities, which can provide a scientific basis for excavating and utilizing planktonic and epiphytic bacterial community resources in the construction of constructed wetlands to improve the efficiency of water purification.

How elevated nitrogen load affects bacterial community structure and nitrogen cycling services in coastal water.

Nutrient pollution in the coastal environment has been accelerated by progressively intensifying aquaculture activities. Excessive nutrients can lead to coastal eutrophication with serious economic and ecological consequences. In this study, we studied coastal planktonic microbial community over a year to understand the aquaculture impact on coastal water quality and function. We observed increased total inorganic nitrogen concentrations in active fish farms to favor the diverse Alpha- and Gammaproteobacteria. Bacterial community alpha diversity in fish farms was positively correlated with total inorganic nitrogen, and active fish farming co-influenced the bacterial structural composition and regional beta diversity. By analyzing the nitrogen cycle-related functional compositions and pathways using PICRUSt2 prediction on inferred genomes, we identified the contribution of over 600 bacterial species to four major pathways. Enhanced nitrogen load in active fish farms was positively correlated with elevated dissimilatory nitrate reduction and denitrification pathway abundances. Fallowed fish farms were characterized by a predicted high abundance of nirA and narB genes contributing to assimilatory nitrate reduction pathway due to the prevalence of Cyanobacteria. Overall, these results suggested active operation and short hiatus in coastal aquaculture practices could rapidly impact planktonic bacterial communities and further influence nitrogen cycling and associated processes. These findings will improve the understanding of the responses and interactions between microbiome and aquaculture activities. In a world of increasing aquaculture demands, this work has important implications for sustainable water resource management and development.

Human access and deterministic processes play a major role in structuring planktonic and sedimentary bacterial and eukaryotic communities in lakes.

Lakes provide habitat for a diverse array of species and offer a wide range of ecosystem services for humanity. However, they are highly vulnerable as they are not only impacted by adverse actions directly affecting them, but also those on the surrounding environment. Improving knowledge on the processes responsible for community assembly in different biotic components will aid in the protection and restoration of lakes. Studies to date suggested a combination of deterministic (where biotic/abiotic factors act on fitness differences amongst taxa) and stochastic (where dispersal plays a larger factor in community assembly) processes are responsible for structuring biotic communities, but there is no consensus on the relative roles these processes play, and data is lacking for lakes. In the present study, we sampled different biotic components in 34 lakes located on the South Island of New Zealand. To obtain a holistic view of assembly processes in lakes we used metabarcoding to investigate bacteria in the sediment and surface waters, and eukaryotes in the sediment and two different size fractions of the water column. Physicochemical parameters were collected in parallel. Results showed that deterministic processes dominated the assembly of lake communities although the relative importance of variable and homogeneous selection differed among the biotic components. Variable selection was more important in the sediment (SSbact and SSeuks) and for the bacterioplankton (Pbact) while the assembly of the eukaryotic plankton (SPeuks, LPeuks) was driven more by homogeneous selection. The ease of human access to the lakes had a significant effect on lake communities. In particular, clade III of SAR11 and Daphnia pulex were only present in lakes with public access. This study provides insights into the distribution patterns of different biotic components and highlights the value in understanding the drivers of different biological communities within lakes.

Hydrological connectivity promotes coalescence of bacterial communities in a floodplain.

Floodplains play essential roles in the ecological functions of regional environments. The merging and coalescence of bacterial communities in aquatic environments results in periodic patterns driven by regular hydrological activities, which may, in turn, influence ecological activities. However, the degree of bacterial community coalescence in the lateral and vertical directions as well as the underlying hydrological mechanism of floodplain ecosystems is poorly understood. Therefore, we investigated the spatiotemporal patterns and coalescence processes of planktonic and sedimentary bacterial communities during normal and high-water periods in a floodplain ecosystem of the Yellow River source region. We classified bacterial operational taxonomic units (OTUs) based on 16S rRNA gene sequencing, and quantified community coalescence by calculating the proportions of overlapping OTUs, the contributions of upstream sources to downstream sinks, and positive/negative cohesion. The results revealed major differences in the composition and diversity of planktonic and sedimentary bacterial communities. Bacterial community diversity in the high-water period was higher than in the normal period. Laterally, hydrological connectivity promoted the immigration and coalescence of bacterial communities to oxbow lakes in both the mainstream and tributaries, with the coalescence degree of planktonic bacteria (2.9%) higher than that of sedimentary bacteria (1.7%). Vertically, the coalescence degree of mainstream planktonic and sedimentary bacterial communities was highest, reaching 2.9%. Co-occurrence network analysis revealed that hydrological connectivity increased the complexity of the bacterial network and enhanced the coalescence of keystone species to oxbow lakes. Furthermore, community coalescence improved the competitiveness and dispersal of bacterial communities. This study demonstrated that coalescence of bacterial communities is driven by hydrological connectivity in a floodplain ecosystem. Further studies should investigate the processes of bacterial community coalescence in floodplains in more detail, which could provide new approaches for environmental protection and ecological function preservation.

Commentary: Addressing the Challenges in Antisepsis: Focus on Povidone Iodine

Topical antimicrobials are essential in wound care as they aid the healing process by preventing and at the same time treating infections in wounds1. Broad spectrum antiseptics with high efficacy towards planktonic and sessile bacterial communities are preferred as wound healing can be delayed by the formation of biofilms often developed by antimicrobial resistant organisms.