Transformations from specialists to generalists cause bacterial communities are more stable than micro-eukaryotic communities under anthropogenic activity disturbance

Stronger biogeographical pattern of bacterioplankton communities than biofilm communities along a riverine ecosystem: A local scale study of the Kaidu river in the arid and semi-arid northwest of China

Although the biogeographical pattern and mechanisms underlying microbial assembly have been well-explored in lentic ecosystems, the relevant scenarios in lotic ecosystems remain poorly understood. By sequencing the bacterial communities in bacterioplankton and biofilm, our study detected their distance-decay relationship (DDR), and the balance between deterministic and stochastic processes, along the Kaidu river in an arid and semi-arid region of northwest China. Our results revealed that bacterioplankton and biofilm had significantly contrasting community structures. The bacterioplankton communities showed a gradually decreasing trend in alpha-diversity from the headwater to the river mouth, contrasting with the alpha-diversity of biofilm communities which was constant along the river length. Both bacterioplankton and biofilm showed significant DDRs along the 500-km river corridor with the slope of the bacterioplankton DDR being steeper than that of the biofilm DDR, which implies a stronger biogeography of bacterioplankton than biofilm. Relative to biofilm communities, the species interactions formed a denser and more complex network in the bacterioplankton communities than in the biofilm communities. Our results also revealed that there was a transition of community assembly from deterministic to stochastic processes upstream to downstream, although both the bacterioplankton and biofilm communities were mainly regulated by deterministic processes within the entire river. All these empirical results expand our knowledge of microbial ecology in an arid and semi-arid lotic ecosystem.

Bacterial specialists playing crucial roles in maintaining system stability and governing microbial diversity in bioremediation of oil-polluted sediments under typical deep-sea condition

Ecologically, interactions and contributions of microbiota generalists and specialists remain largely unexplored in remediation of deep-sea oil pollution. Herein, ecological and evolutionary characteristics of the two taxa were comprehensively investigated in restoration of oil-polluted sediment at deep-sea microcosm. Niche-specialized taxa exhibited rapid speciation rate, more complex network structure and highly interspecific mutualism. In contrast, generalists possessed higher richness but with poor local performance, as evidenced by higher extinction rate, lower stability, and more interspecific antagonism. Generalists were the primary oil degraders, while specialists acted as auxiliaries promoting degradation via production of biofilm and biosurfactant. Evolutionarily, the continuous transition from specialists to generalists insured the exclusion of generalist at a relatively constant level for ecological trade-offs. Collectively, the findings emphasize the importance of specialists in facilitating oil degradation by elucidating their vital roles in maintaining system stability and regulating microbial diversity during process, and offer valuable guidance for designing remediation plans.

Spatiotemporal dynamics of dinoflagellate communities in the Taiwan Strait and their correlations with micro-eukaryotic and bacterial communities

Dinoflagellate blooms have negative adverse effects on marine ecosystems. However, our knowledge about the spatiotemporal distribution of dinoflagellate communities and their correlations with micro-eukaryotic and bacterial communities is still rare. Here, the sediment micro-eukaryotic and bacterial communities were explored in the Taiwan Strait (TWS) by 16S and 18S rRNA gene high-throughput sequencing. We found that the dinoflagellates were the most abundant algal group in TWS, and their relative abundance was higher in spring and autumn than in summer. Moreover, the species richness and community composition of dinoflagellates showed strong seasonal patterns. NO3-N and NH4-N had the strongest correlations with the spatiotemporal dynamics of community composition of dinoflagellates. The dinoflagellates had a significantly wider niche breadth than other algal groups for NH4-N, NO3-N and NO2-N, and therefore potentially contributed to a wider distribution range and high abundance in TWS. In addition, the dinoflagellates had stronger impacts on microeukaryotes than on bacteria for both community composition and species richness. However, the dinoflagellates showed close coexistence with bacteria but loose coexistence with microeukaryotes in spring co-occurrence networks. This close coexistence suggests the potentially strong synergy effects between dinoflagellates and bacteria in spring dinoflagellate blooms in TWS. Overall, this study revealed the distribution mechanisms of dinoflagellates in TWS based on niche breadth and also unveiled the different effects of dinoflagellates on micro-eukaryotic and bacterial communities.

Differential microbiome features in lake-river systems of Taihu basin in response to water flow disturbance

Introduction

In riverine ecosystems, dynamic interplay between hydrological conditions, such as flow rate, water level, and rainfall, significantly shape the structure and function of bacterial and microeukaryotic communities, with consequences for biogeochemical cycles and ecological stability. Lake Taihu, one of China's largest freshwater lakes, frequently experiences cyanobacterial blooms primarily driven by nutrient over-enrichment and hydrological changes, posing severe threats to water quality, aquatic life, and surrounding human populations. This study explored how varying water flow disturbances influence microbial diversity and community assembly within the interconnected river-lake systems of the East and South of Lake Taihu (ET&ST). The Taipu River in the ET region accounts for nearly one-third of Lake Taihu's outflow, while the ST region includes the Changdougang and Xiaomeigang rivers, which act as inflow rivers. These two rivers not only channel water into Lake Taihu but can also cause the backflow of lake water into the rivers, creating distinct river-lake systems subjected to different intensities of water flow disturbances.

Methods

Utilizing high-throughput sequencing, we selected 22 sampling sites in the ET and ST interconnected river-lake systems and conducted seasonally assessments of bacterial and microeukaryotic community dynamics. We then compared differences in microbial diversity, community assembly, and co-occurrence networks between the two regions under varying hydrological regimes.

Results and discussion

This study demonstrated that water flow intensity and temperature disturbances significantly influenced diversity, community structure, community assembly, ecological niches, and coexistence networks of bacterial and eukaryotic microbes. In the ET region, where water flow disturbances were stronger, microbial richness significantly increased, and phylogenetic relationships were closer, yet variations in community structure were greater than in the ST region, which experienced milder water flow disturbances. Additionally, migration and dispersal rates of microbes in the ET region, along with the impact of dispersal limitations, were significantly higher than in the ST region. High flow disturbances notably reduced microbial niche width and overlap, decreasing the complexity and stability of microbial coexistence networks. Moreover, path analysis indicated that microeukaryotic communities exhibited a stronger response to water flow disturbances than bacterial communities. Our findings underscore the critical need to consider the effects of hydrological disturbance on microbial diversity, community assembly, and coexistence networks when developing strategies to manage and protect river-lake ecosystems, particularly in efforts to control cyanobacterial blooms in Lake Taihu.

Urban greenspace types and climate factors jointly drive the microbial community structure and co-occurrence network

The benefits of urban green space are socially widely recognized as a direct link between plant-microbe interactions and the maintenance of biodiversity, community stability, and ecosystem functioning. Nevertheless, there is a lack of knowledge about the factors influencing microbial communities in urban green spaces, especially those related to phyllosphere epiphytes and stem epiphytes. In this study, we analyzed the microbial community assembly in leaf and stem bark samples collected from Square, Road, Campus, and Park. Illumina sequecing of 16S amplicons was performed to characterize microbial diversity and composition. The α-diversity was significantly higher in the bark epiphytic community, compared to the phyllosphere. Moreover, urban greenspaces'type altered the way communities gathered. The main soil and air properties factors of the urban greenhouse (e.g. soil temperature, atmospheric moisture, air temperature) were shaping the characteristics of bacterial communities on the leaf surface and bark epiphytic. In addition, in the co-occurrence network analysis, keystone taxa were not mostly observed in abundant species, which may be necessary to maintain ecosystem functions. Finally, our findings provide a deeper understanding of the ecological dynamics and microbial interactions within plant phyllosphere and stem epiphytes microbiomes.

A global survey of host, aquatic, and soil microbiomes reveals shared abundance and genomic features between bacterial and fungal generalists

Environmental change, coupled with alteration in human lifestyles, is profoundly impacting the microbial communities critical to the health of the Earth and its inhabitants. To identify bacteria and fungi that are resistant and susceptible to habitat change, we analyze thousands of genera detected in 1,580 host, soil, and aquatic samples. This large-scale analysis identifies 48 bacterial and 4 fungal genera that are abundant across the three biomes, demonstrating fitness in diverse environmental conditions. Samples containing these generalists have significantly higher alpha diversity. These generalists play a significant role in shaping cross-kingdom community structure, boasting larger genomes with more secondary metabolism and antimicrobial resistance genes. Conversely, 30 bacterial and 19 fungal genera are only found in a single habitat, suggesting a limited ability to adapt to different and changing environments. These findings contribute to our understanding of microbial niche breadth and its consequences for global biodiversity loss.

Changing dynamics of antibiotic resistant Escherichia in Caspian gulls shows the importance of longitudinal environmental studies

This study is focused on Escherichia spp. isolates resistant to critically important antibiotics (cefotaxime, ciprofloxacin and colistin) among Caspian gull's (Larus cachinnans) chicks nesting in the Nove Mlyny Water Reservoir, Czech Republic. The prevalence of antimicrobial resistance (AMR) in bacteria within wild birds is commonly evaluated using a single sampling event, capturing only a brief and momentary snapshot at a particular location. Therefore, the Caspian gulls in our study were sampled in May 2018 (n = 72) and May 2019 (n = 45), and a water sample was taken from the reservoir (2019). We obtained 197 isolates identified as E. coli by MALDI-TOF MS. A total of 158 representative isolates were whole-genome sequenced, 17 isolates were then reclassified to Escherichia albertii. We observed a higher (86 %; 62/72) occurrence of ESBL/AmpC-producing Escherichia spp. among gulls in 2018 compared to 38 % (17/45) in 2019 (p < 0.00001). The decrease in prevalence was linked to clonal lineage of E. coli ST11893 predominating in 2018 which carried blaCMY-2 and which was not recovered from the gulls in 2019. Oppositely, several Escherichia STs were found in gulls from both years as well as in the water sample including STs commonly recognized as internationally high-risk lineages such as ST10, ST58, ST88, ST117, ST648 or ST744. Phylogenetic analysis of E. coli from EnteroBase from countries where these particular gulls wander revealed that some STs are commonly found in various sources including humans and a portion of them is even closely related (up to 100 SNPs) to our isolates. We demonstrated that the occurrence of AMR in Escherichia can vary greatly in time in synanthropic birds and we detected both, a temporary prevalent lineage and several persistent STs. The close relatedness of isolates from gulls and isolates from EnteroBase highlights the need to further evaluate the risk connected to wandering birds.

Seasonal variation and human impacts of the river biofilm bacterial communities in the Shiting River in southeastern China

Bacterial communities in epilithic biofilm plays an important role in biogeochemistry processes in freshwater ecosystems. Nevertheless, our understanding of the geographical and seasonal variations of the composition of bacterial communities in the biofilm of gravels on river bed is still limited. Various anthropogenic activities also influence the biofilm bacteria in gravel rivers. By taking the Shiting River in the upper Yangtze River basin in Sichuan Province as an example, we studied the geographical and seasonal variations of epilithic bacteria and the impacts of weirs and other human activities (e.g., sewage pollution). The river has experienced severe degradation since the Ms 8.0 Wenchuan Earthquake, and weirs were constructed to prevent bed erosion. We collected epilithic biofilms samples at 17 sites along ~ 30 km river reach of the Shiting River in the autumn of 2021 and the summer of 2022, respectively. We applied 16S rRNA gene high-throughput sequencing technology and Functional Annotation of Prokaryotic Taxa (FAPROTAX) to analyze the seasonal and biogeographic patterns and potential functions of the biofilm bacterial communities. The results showed that epilithic bacteria from the two surveys exhibited variation in community composition, bacterial diversity and potential functions. The bacteria samples collected in the autumn have much higher alpha diversity and richness than those collected in the summer. Bacterial richness and diversity were lower downstream of the weirs than upstream. Low diversity was observed at a sampling site influenced by sewage inflow, which contains high level of nitrogen-related chemicals.

Greater transmission capacities and small-world characteristics of bacterial communities in the above- than those in the below- ground niches of a typical submerged macrophyte, Vallisneria natans

Leaves and roots of submerged macrophytes provide extended surfaces and stable internal tissues for distinct microorganisms to rest, but how these microorganisms interact with each other across different niches and ultimately drive the distribution through horizontal and vertical transmissions remains largely undetermined. Knowledge of the mechanisms of assemblage and transmission in aquatic macrophytes-associated microbial communities will help to better understanding their important roles in plant fitness and benefit ecological functions. Here, we conducted a microcosmic experiment based on in situ lake samples to investigate the bacterial community assemblage, transmission, and co-occurrence patterns in different niches of a typical submerged macrophyte, Vallisneria natans (V. natans), including seed endosphere, as well as environmental (water and bulk sediment), epiphytic (phyllosphere and rhizosphere), and endophytic (leaf and root endosphere) microhabitats of both leaves and roots representatives of the above- and below- ground niches (AGNs and BGNs), respectively. We found the bacterial communities colonized in epiphytic niches not only exhibited the highest diversity compared to adjacent environmental and endophytic niches, but also dominated the interactions between those bacterial members of neighboring niches in both AGNs and BGNs. The host plants promoted niche specificity at bacterial community-level, as confirmed by the proportion of bacterial specialists increased with plant proximity, especially in the BGNs. Furthermore, the bacterial taxa colonized in the AGNs exhibited higher horizontal and vertical transmission capacities than those in the BGNs, especially in the vertical transmission from seeds to leaves (41.38 %) than roots (0.42 %). Meanwhile, the bacterial co-occurrence network in AGNs was shown to have stronger small-world characteristics but weaker stability than those in the BGNs. Overall, this study cast new light on the plant microbiome in the aquatic environment, thus better promoting the potential development of strategies for breeding aquatic macrophyte holobiont with enhanced water purification and pollutant removal capabilities in the future.

Exploring the efficacy of metabarcoding and non-target screening for detecting treated wastewater

Wastewater treatment processes can eliminate many pollutants, yet remainder pollutants contain organic compounds and microorganisms released into ecosystems. These remainder pollutants have the potential to adversely impact downstream ecosystem processes, but their presence is currently not being monitored. This study was set out with the aim of investigating the effectiveness and sensitivity of non-target screening of chemical compounds, 18S V9 rRNA gene, and full-length 16S rRNA gene metabarcoding techniques for detecting treated wastewater in receiving waters. We aimed at assessing the impact of introducing 33 % treated wastewater into a triplicated large-scale mesocosm setup during a 10-day exposure period. Discharge of treated wastewater significantly altered the chemical signature as well as the microeukaryotic and prokaryotic diversity of the mesocosms. Non-target screening, 18S V9 rRNA gene, and full-length 16S rRNA gene metabarcoding detected these changes with significant covariation of the detected pattern between methods. The 18S V9 rRNA gene metabarcoding exhibited superior sensitivity immediately following the introduction of treated wastewater and remained one of the top-performing methods throughout the study. Full-length 16S rRNA gene metabarcoding demonstrated sensitivity only in the initial hour, but became insignificant thereafter. The non-target screening approach was effective throughout the experiment and in contrast to the metabarcoding methods the signal to noise ratio remained similar during the experiment resulting in an increasing relative strength of this method. Based on our findings, we conclude that all methods employed for monitoring environmental disturbances from various sources are suitable. The distinguishing factor of these methods is their ability to detect unknown pollutants and organisms, which sets them apart from previously utilized approaches and allows for a more comprehensive perspective. Given their diverse strengths, particularly in terms of temporal resolution, these methods are best suited as complementary approaches.

Continuous cultivation of mixed-culture microalgae using anaerobic digestion effluent in photobioreactors with different strategies for adjusting nitrogen loading rate

This study examined continuous mixed-culture microalgae cultivation for nutrient removal from anaerobic digestion (AD) effluents in photobioreactors, while altering the NH4+-N loading rate (NLR) by adjusting either the hydraulic retention time (HRT) (reactor set RH) or the influent NH4+-N concentration (reactor set RS). Both RH and RS demonstrated efficient nutrient removal and microalgae cultivation at NLRs of 4-10 mg NH4+-N/L∙d, reaching peak performance at 10 mg NH4+-N/L∙d. Within this range, RH obtained greater biomass yield and productivity, while RS maintained higher microalgal concentrations. The cultivated biomasses obtained from RH and RS had good settleability and suitable fatty acid compositions as a biodiesel feedstock, although their organic composition varied considerably with NLR and HRT. Parachlorella overwhelmingly dominated the reactors' microalgal communities throughout the experiment, co-existing with various microalgae-associated bacteria. Changes in NLR significantly influenced the bacterial community structures, underscoring its critical role in determining reactor performance and microalgal-bacterial community behavior.

Urban greenspace types influence the microbial community assembly and antibiotic resistome more in the phyllosphere than in the soil

Urban greenspace (UGS) is recognized to confer significant societal benefits, but few studies explored the microbial communities and antibiotic resistance genes (ARGs) from different urban greenspace types. Here, we collected leaf and soil samples from forest, greenbelt, and parkland to analyze microbial community assembly and ARG profile. For phyllosphere fungal community, the α-diversity was higher in forest, compared to those in greenbelt and parkland. Moreover, urban greenspace types altered the community assembly. Stochastic processes had a greater effect on phyllosphere fungal community in greenbelt and parkland, while in forest they were dominated by deterministic processes. In contrast, no significant differences in bacterial community diversity, community assembly were observed between the samples collected from different urban greenspace types. A total of 153 ARGs and mobile genetic elements (MGEs) were detected in phyllosphere and soil with resistance to the majority classes of antibiotics commonly applied to humans and animals. Structural equation model further revealed that a direct association between greenspace type and ARGs in the phyllosphere even after considering the effects of all other factors simultaneously. Our findings provide new insights into the microbial communities and antibiotic resistome of urban greenspaces and the potential risk linked with human health.

Irreversible community difference between bacterioplankton generalists and specialists in response to lake dredging

Understanding response of bacterioplankton community responsible for maintaining ecological functions of aquatic ecosystems to environmental disturbance is an important subject. However, it remains largely unclear how bacterioplankton generalists and specialists respond to dredging disturbance. Illumina MiSeq sequencing and statistical analyses were used to evaluate landscape patterns, evolutionary potentials, environmental adaptability, and community assembly processes of generalists and specialists in response to dredging in eutrophic Lake Nanhu. The Proteobacteria and Actinobacteria dominated bacterioplankton communities of generalists and specialists, and abundances of Proteobacteria decreased and Actinobacteria increased after dredging. The generalists displayed higher phylogenetic distance, richness difference, speciation rate, extinction rate, and diversification rate as well as stronger environmental adaptation than that of specialists. In contrast, the specialists rather than generalists showed higher community diversity, taxonomic distance, and species replacement as well as closer phylogenetic clustering. Stochastic processes dominated community assemblies of generalists and specialists, and stochasticity exhibited a larger effect on community assembly of generalists rather than specialists. Our results emphasized that lake dredging could change landscape patterns of bacterioplankton generalists and specialists, whereas the short-term dredging conducted within one year was unable to reverse community difference between generalists and specialists. Our findings extend our understanding of how bacterioplankton generalists and specialists responding to dredging disturbance, and these findings might in turn call on long-term dredging for better ecological restoration of eutrophic lakes.

Contrasting response of microeukaryotic and bacterial communities to the interplay of seasonality and local stressors in shallow soda lakes

Seasonal environmental variation is a leading driver of microbial planktonic community assembly and interactions. However, departures from usual seasonal trends are often reported. To understand the role of local stressors in modifying seasonal succession, we sampled fortnightly, throughout three seasons, five nearby shallow soda lakes exposed to identical seasonal and meteorological changes. We characterised their microeukaryotic and bacterial communities by amplicon sequencing of the 16S and 18S rRNA gene, respectively. Biological interactions were inferred by analyses of synchronous and time-shifted interaction networks, and the keystone taxa of the communities were topologically identified. The lakes showed similar succession patterns during the study period with spring being characterised by the relevance of trophic interactions and a certain level of community stability followed by a more dynamic and variable summer-autumn period. Adaptation to general seasonal changes happened through shared core microbiome of the lakes. Stochastic events such as desiccation disrupted common network attributes and introduced shifts from the prevalent seasonal trajectory. Our results demonstrated that, despite being extreme and highly variable habitats, shallow soda lakes exhibit certain similarities in the seasonality of their planktonic communities, yet local stressors such as droughts instigate deviations from prevalent trends to a greater extent for microeukaryotic than for bacterial communities.

Diversity and interaction of bacterial and microeukaryotic communities in sediments planted with different submerged macrophytes: Responses to decabromodiphenyl ether

Although various persistent organic pollutants (POPs) can affect microbial communities and functions in aquatic ecosystems, little is known about how bacteria and microeukaryotes respond to the POPs in sediments planted with different submerged macrophytes. Here, a 60-day microcosm experiment was carried out to investigate the changes in the diversity and interaction of bacterial and microeukaryotic communities in sediments collected from Taihu lake, either with decabromodiphenyl ether (BDE-209) own or combined with two common submerged macrophyte species (Vallisneria natans and Hydrilla verticillate). The results showed that BDE-209 significantly decreased the bacterial α-diversity but increased the microeukaryotic one. In sediments planted with submerged macrophytes, the negative effect of BDE-209 on bacterial diversity was weakened, and its positive effect on microeukaryotic one was strengthened. Co-occurrence network analysis revealed that the negative relationship was dominant in bacterial and microeukaryotic communities, while the cooperative relationship between microbial species was increased in planted sediments. Among nine keystone species, one belonging to bacterial family Thermoanaerobaculaceae was enriched by BDE-209, and others were inhibited. Notably, such inhibition was weakened, and the stimulation was enhanced in planted sediments. Together, these observations indicate that the responses of bacteria and microeukaryotes to BDE-209 are different, and their communities under BDE-209 contamination are more stable in sediments planted with submerged macrophytes. Moreover, the effects of plant species on the microbial responses to BDE-209 need to be explored by more specific field studies in the future.

Microbial sensitivity to temperature and sulfate deposition modulates greenhouse gas emissions from peat soils

Peatlands are among the largest natural sources of atmospheric methane (CH₄ ) worldwide. Microbial processes play a key role in regulating CH₄ emissions from peatland ecosystems, yet the complex interplay between soil substrates and microbial communities in controlling CH₄ emissions as a function of global change remains unclear. Herein, we performed an integrated analysis of multi-omics data sets to provide a comprehensive understanding of the molecular processes driving changes in greenhouse gas (GHG) emissions in peatland ecosystems with increasing temperature and sulfate deposition in a laboratory incubation study. We sought to first investigate how increasing temperatures (4, 21, and 35°C) impact soil microbiome-metabolome interactions; then explore the competition between methanogens and sulfate-reducing bacteria (SRBs) with increasing sulfate concentrations at the optimum temperature for methanogenesis. Our results revealed that peat soil organic matter degradation, mediated by biotic and potentially abiotic processes, is the main driver of the increase in CO₂ production with temperature. In contrast, the decrease in CH₄ production at 35°C was linked to the absence of syntrophic communities and the potential inhibitory effect of phenols on methanogens. Elevated temperatures further induced the microbial communities to develop high growth yield and stress tolerator trait-based strategies leading to a shift in their composition and function. On the other hand, SRBs were able to outcompete methanogens in the presence of non-limiting sulfate concentrations at 21°C, thereby reducing CH₄ emissions. At higher sulfate concentrations, however, the prevalence of communities capable of producing sufficient low-molecular-weight carbon substrates for the coexistence of SRBs and methanogens was translated into elevated CH₄ emissions. The use of omics in this study enhanced our understanding of the structure and interactions among microbes with the abiotic components of the system that can be useful for mitigating GHG emissions from peatland ecosystems in the face of global change.

Changes of In Situ Prokaryotic and Eukaryotic Communities in the Upper Sanya River to the Sea over a Nine-Hour Period

The transition areas of riverine, estuarine, and marine environments are particularly valuable for the research of microbial ecology, biogeochemical processes, and other physical-chemical studies. Although a large number of microbial-related studies have been conducted within such systems, the vast majority of sampling have been conducted over a large span of time and distance, which may lead to separate batches of samples receiving interference from different factors, thus increasing or decreasing the variability between samples to some extent. In this study, a new in situ filtration system was used to collect membrane samples from six different sampling sites along the Sanya River, from upstream freshwater to the sea, over a nine-hour period. We used high-throughput sequencing of 16S and 18S rRNA genes to analyze the diversity and composition of prokaryotic and eukaryotic communities. The results showed that the structures of these communities varied according to the different sampling sites. The α-diversity of the prokaryotic and eukaryotic communities both decreased gradually along the downstream course. The structural composition of prokaryotic and eukaryotic communities changed continuously with the direction of river flow; for example, the relative abundances of Rhodobacteraceae and Flavobacteriaceae increased with distance downstream, while Sporichthyaceae and Comamonadaceae decreased. Some prokaryotic taxa, such as Phycisphaeraceae and Chromobacteriaceae, were present nearly exclusively in pure freshwater environments, while some additional prokaryotic taxa, including the SAR86 clade, Clade I, AEGEAN-169 marine group, and Actinomarinaceae, were barely present in pure freshwater environments. The eukaryotic communities were mainly composed of the Chlorellales X, Chlamydomonadales X, Sphaeropleales X, Trebouxiophyceae XX, Annelida XX, and Heteroconchia. The prokaryotic and eukaryotic communities were split into abundant, common, and rare communities for NCM analysis, respectively, and the results showed that assembly of the rare community assembly was more impacted by stochastic processes and less restricted by species dispersal than that of abundant and common microbial communities for both prokaryotes and eukaryotes. Overall, this study provides a valuable reference and new perspectives on microbial ecology during the transition from freshwater rivers to estuaries and the sea.

Nutrient Removal in Eutrophic Water Promotes Stability of Planktonic Bacterial and Protist Communities

Nutrient (nitrogen and phosphorus) removal by using bioremediation technologies in eutrophic water alters bacterial and protist community structure and function, but how it changes the stability of community remains unclear. To fill this gap, in this study, bacterial and protist communities were investigated using 16S and 18S rRNA gene high-throughput sequencing during the nutrient removal by using ecological floating beds of Canna indica L. Our results showed that both bacterial and protist community compositions in the treatment group were similar to those in the control group at the beginning of the experiment (day 1 to day 11), but then bacterial and protist community compositions became more stable with the removal of nutrients in the treatment group than those in the control group (day 12 to day 18). We further explored the mechanisms for this increased stability and found that the contribution of the stochastic process to bacterial and protist community variations was higher in the control group than that in the treatment group. This suggests that the high nutrient concentration in the control group might increase the random colonization or extinction, and therefore resulted in the high temporal variability (i.e., unstable) of bacterial and protist communities. Our findings suggest that bioremediation for eutrophication can promote the stability of aquatic communities, and therefore potentially maintain aquatic ecosystem functions and services to humanity.

Impact of Climate and Slope Aspects on the Composition of Soil Bacterial Communities Involved in Pedogenetic Processes along the Chilean Coastal Cordillera

Soil bacteria play a fundamental role in pedogenesis. However, knowledge about both the impact of climate and slope aspects on microbial communities and the consequences of these items in pedogenesis is lacking. Therefore, soil-bacterial communities from four sites and two different aspects along the climate gradient of the Chilean Coastal Cordillera were investigated. Using a combination of microbiological and physicochemical methods, soils that developed in arid, semi-arid, mediterranean, and humid climates were analyzed. Proteobacteria, Acidobacteria, Chloroflexi, Verrucomicrobia, and Planctomycetes were found to increase in abundance from arid to humid climates, while Actinobacteria and Gemmatimonadetes decreased along the transect. Bacterial-community structure varied with climate and aspect and was influenced by pH, bulk density, plant-available phosphorus, clay, and total organic-matter content. Higher bacterial specialization was found in arid and humid climates and on the south-facing slope and was likely promoted by stable microclimatic conditions. The presence of specialists was associated with ecosystem-functional traits, which shifted from pioneers that accumulated organic matter in arid climates to organic decomposers in humid climates. These findings provide new perspectives on how climate and slope aspects influence the composition and functional capabilities of bacteria, with most of these capabilities being involved in pedogenetic processes.