Community composition and activity of prokaryotes associated to detrital particles in two contrasting lake ecosystems

The composition, distribution and extracellular enzyme activities of bacteria attached to small (2-50 microm in size) transparent exopolymer and Coomassie-stained proteinaceous particles (TEP and CSP) were examined in two lakes of different trophic status located in the Massif Central of France. TEP concentrations (10(4)-10(6) particle per L) were significantly higher in the more productive lake and were significantly related to chlorophyll a concentrations. The majority of TEP and CSP were colonized by bacteria that constituted 2.6% and 7.4% of the total 4',6-diamidino-2-phenylindole-stained bacteria in lakes Pavin and Aydat, respectively. In both lakes, the composition of particle-associated bacteria was different from that of free-living bacteria, the Betaproteobacteria and Bacteroidetes (i.e. former Cytophaga-Flavobacteria group) being the dominant groups on particles. We also found that 2-5 microm TEP were more colonized than 2-5 microm CSP in the two lakes, and that TEP colonization was higher in the less productive lake. Measurements of Leucine aminopeptidase and alpha-glucosidase activities in fractionated lake water (0.2-1.2, 1.2-5 and >5 microm fractions) indicated that proteolytic activity was always higher and that particle-associated bacteria have higher enzymatic activities than free-living bacteria. The glycolytic activities in the 1.2-5 and >5 microm fractions were related to the abundance of TEP. We conclude that small freshwater detrital organic particles constitute microhabitats with high bacterial activities in pelagic environments and, undoubtedly, present significant ecological implications for the prokaryotic community structure and function in aquatic ecosystems.     

Effect of grazers and viruses on bacterial community structure and production in two contrasting trophic lakes

Background

Over the last 30 years, extensive studies have revealed the crucial roles played by microbes in aquatic ecosystems. It has been shown that bacteria, viruses and protozoan grazers are dominant in terms of abundance and biomass. The frequent interactions between these microbiological compartments are responsible for strong trophic links from dissolved organic matter to higher trophic levels, via heterotrophic bacteria, which form the basis for the important biogeochemical roles of microbial food webs in aquatic ecosystems. To gain a better understanding of the interactions between bacteria, viruses and flagellates in lacustrine ecosystems, we investigated the effect of protistan bacterivory on bacterial abundance, production and structure [determined by 16S rRNA PCR-DGGE], and viral abundance and activity of two lakes of contrasting trophic status. Four experiments were conducted in the oligotrophic Lake Annecy and the mesotrophic Lake Bourget over two seasons (early spring vs. summer) using a fractionation approach. In situ dark vs. light incubations were performed to consider the effects of the different treatments in the presence and absence of phototrophic activity.

Results

The presence of grazers (i.e. < 5-μm small eukaryotes) affected viral production positively in all experiments, and the stimulation of viral production (compared to the treatment with no eukaryotic predators) was more variable between lakes than between seasons, with the highest value having been recorded in the mesotrophic lake (+30%). Viral lysis and grazing activities acted additively to sustain high bacterial production in all experiments. Nevertheless, the stimulation of bacterial production was more variable between seasons than between lakes, with the highest values obtained in summer (+33.5% and +37.5% in Lakes Bourget and Annecy, respectively). The presence of both predators (nanoflagellates and viruses) did not seem to have a clear influence upon bacterial community structure according to the four experiments.

Conclusions

Our results highlight the importance of a synergistic effect, i.e. the positive influence of grazers on viral activities in sustaining (directly and indirectly) bacterial production and affecting composition, in both oligotrophic and mesotrophic lakes.     

Anaerobic methane oxidation potential and bacteria in freshwater lakes: Seasonal changes and the influence of trophic status

Nitrite-dependent anaerobic methane oxidation (n-damo), mainly carried out by n-damo bacteria, is an important pathway for mitigating methane emission from freshwater lakes. Although n-damo bacteria have been detected in a variety of freshwater lakes, their potential and distribution, and associated environmental factors, remain unclear. Therefore, the current study investigated the potential and distribution of anaerobic methanotrophs in sediments from Erhai Lake and Dianchi Lake, two adjacent freshwater lakes in the Yunnan Plateau with different trophic status. Both lakes showed active anaerobic methane oxidation potential and harbored a high density of n-damo bacteria. Based on the n-damo pmoA gene, sediment n-damo bacterial communities mainly consisted of Candidatus Methylomirabils oxyfera and Candidatus Methylomirabils sinica, as well as novel n-damo organisms. Sediment anaerobic methane oxidation potential and the n-damo bacterial community showed notable differences among seasons and between lakes. The environmental variables associated with lake trophic status (e.g. total nitrogen, ammonia nitrogen, nitrate nitrogen, and total organic carbon) might have significant impacts on the anaerobic methane oxidation potential, as well as the abundance and community structure of n-damo bacteria. Therefore, trophic status could determine the n-damo process in freshwater lake sediment.     

龙感湖沉积物泥芯硅藻群落和营养状态的反演

The importance of aquatic vegetation to the ecologi-cal restoration has been recognized commonly bylimnolo-gists and lake managements[1—4].As to the ecologicalrestoration in eutrophicated lakes,it is of great signifi-cance to knowthe dynamic process of the ecosystemevo-lution in a macrophyte-dominated lake under the humanimpacts in historical period,to make it clear whether thecommunitystructure and ecological function would be af-fected bythe extension of the vegetation growth,tofind asolutionto remain ste...     

Influence of environmental conditions, bacterial activity and viability on the viral component in 10 Antarctic lakes

The influence of biotic and environmental variables on the abundance of virus-like particles (VLP) and lysogeny was investigated by examining 10 Antarctic lakes in the Vestfold Hills, Antarctica, in the Austral Spring. Abundances of viruses and bacteria and bacterial metabolic activity were estimated using SYBR Gold (Molecular Probes), Baclight (Molecular Probes) and 6-carboxy fluorescein diacetate (6CFDA). Total bacterial abundances among the lakes ranged between 0.12 and 0.47 x 10(9) cells L(-1). The proportion of intact bacteria (SYTO 9-stained cells) ranged from 13.5% to 83.5% of the total while active (6CFDA-stained) bacteria ranged from 33% to 116%. Lysogeny, as determined with Mitomycin C, was only detected in one of the lakes surveyed, indicating that viral replication was occurring predominantly via the lytic cycle. Principal component analysis and confirmatory correlation analysis of individual variables showed that high abundances of VLP occurred in lakes of high conductivity with high concentrations of soluble reactive phosphorus and dissolved organic carbon. These lakes supported high concentrations of chlorophyll a, intact bacteria, rates of bacterial production and virus to bacteria ratios. Thus, it was suggested that viral abundance in the Antarctic lakes was determined by the trophic status of the lake and the resultant abundance of intact bacterial hosts.     

Coupling Between Rates of Bacterial Production and the Abundance of Metabolically Active Bacteria in Lakes, Enumerated Using CTC Reduction and Flow Cytometry

Abstract In natural bacterioplankton assemblages, only a fraction of the total cell count is active, and, therefore, rates of bacterial production should be more strongly correlated to the number of active cells than to the total number of bacteria. However, this hypothesis has seldom been tested. Herein we explore the relationship between rates of bacterial production (measured as leucine uptake) and the number of active bacteria in 14 lakes in southern Québec. Active bacteria are defined as those cells capable of reducing the tetrazolium salt CTC to its fluorescent formazan; these cells were enumerated using flow cytometry. Bacterial production varied two orders of magnitude in the lakes studied, as did the number of active bacteria, whereas the total number of bacteria varied by only sixfold. The number and proportion of active bacteria were similar among lake strata, but rates of bacterial production were highest in the epilimnion and lowest in the hypolimnion. As expected, bacterial production was better correlated to the number of active cells, and bacterial growth rates calculated for active cells ranged from 0.7 to 1.8 day⁻¹, on average threefold higher than those calculated on the basis of total bacterial abundance. Growth rates scaled to active cells were, on average, similar among lake strata and did not show any pattern along a gradient of increasing chlorophyll concentration, so there was no systematic change of bacterial growth rates with lake productivity. In contrast, growth rates scaled to the entire bacterial assemblage were positively correlated to chlorophyll, were tenfold more variable among lakes than growth rates of active cells, and showed larger differences among lake strata. Scaling bacterial production to either the total number or the number of active cells thus results in very different patterns in bacterial growth rates among aquatic systems. Received: 12 July 1996; Accepted: 24 September 1996     

Bird abundance and species richness on Florida lakes: influence of trophic status,lake morphology,and aquatic macrophytes

Data from 46 Florida lakes were used to examine relationships between bird abundance (numbers and biomass) and species richness, and lake trophic status, lake morphology and aquatic macrophyte abundance. Average annual bird numbers ranged from 7 to 800 birds km^–2 and bird biomass ranged from 1 to 465 kg km^–2. Total species richness ranged from 1 to 30 species per lake. Annual average bird numbers and biomass were positively correlated to lake trophic status as assessed by total phosphorus (r = 0.61), total nitrogen (r = 0.60) and chlorophyll a (r = 0.56) concentrations. Species richness was positively correlated to lake area (r = 0.86) and trophic status (r = 0.64 for total phosphorus concentrations). The percentage of the total annual phosphorus load contributed to 14 Florida lakes by bird populations was low averaging 2.4%. Bird populations using Florida lakes, therefore, do not significantly impact the trophic status of the lakes under natural situations, but lake trophic status is a major factor influencing bird abundance and species richness on lakes. Bird abundance and species richness were not significantly correlated to other lake morphology or aquatic macrophyte parameters after the effects of lake area and trophic status were accounted for using stepwise multiple regression. The lack of significant relations between annual average bird abundance and species richness and macrophyte abundance seems to be related to changes in bird species composition. Bird abundance and species richness remain relatively stable as macrophyte abundance increases, but birds that use open-water habitats (e.g., double-crested cormorant, Phalacrocorax auritus) are replaced by species that use macrophyte communities (e.g., ring-necked duck, Aythya collaris).     

Bacterial Production in the Recently Flooded Sep Reservoir: Diel Changes in Relation to Dissolved Carbohydrates and Combined Amino Acids

The spatial distribution of bacterial abundance and production were measured every 4 h in a recently flooded oligo-mesotrophic reservoir (the Sep Reservoir, Puy-De-Dôme, France), in relation to concentrations of dissolved carbohydrates and combined amino acids. The concentration of dissolved organic matter (DOM) components in the recently flooded Sep Reservoir were higher than those measured in other lakes of similar trophic status. Short-term variations in the bacterial production in this new reservoir appeared cyclical and endogenous to bacterial communities. These results highlight the need for the evaluation of diel changes in bacterial production, if estimation of the daily production rate of bacteria is to be done accurately for a reliable model of carbon flow through bacterioplankton and ultimately through aquatic microbial food webs. Bacterial growth, measured over time and space, did not appear exclusively governed by DOM components from phytoplankton primary production.     

Increased Diversity of Predacious <Emphasis Type="Italic">Bdellovibrio</Emphasis>-Like Organisms (BLOs) as a Function of Eutrophication in Kumaon Lakes of India

Predation by Bdellovibrio-like organisms (BLOs) results in bacterial community succession in aquatic ecosystems. The effects of nutrient loading on the distribution and phylogeny of BLOs remain largely unknown. To this end, we present our findings on BLO diversity from four north-Indian lakes that are variable in their trophic status; Nainital is eutrophic, both, Bhimtal and Naukuchiatal are mesotrophic and Sattal remains oligotrophic, respectively. Initially, total heterotrophic bacteria and BLOs were quantified by most probable number (MPN) analyses using Pseudomonas putida and Escherichia coli as prey bacteria. Total bacterial numbers were at least two-logs higher in the eutrophic lake samples compared with oligotrophic lake. Similarly, BLO numbers were approximately 39-fold higher using Pseudomonas sp., which is likely the preferred prey within these lakes. Conversely, significant differences were not observed between mesotrophic and oligotrophic BLO numbers when E. coli was used as the prey. PCR-RFLP of small subunit rDNA (SSU rDNA) of BLOs, followed by cloning, sequencing, and taxonomic categorization revealed distinct differences such that, eutrophic lake consisted of higher BLO diversity compared with mesotrophic and oligotrophic lake, most likely due to both, higher numbers and availability of a diverse population of prey bacteria resulting from nutrient loading in this ecosystem.     

Temporal and spatial variations of aquatic environmental characteristics and sediment bacterial community in five regions of Lake Taihu

Sediment bacterial community and their relation with environmental factors were investigated in the five different trophic status lake regions sediment, Meiliang Bay, Wuli Lake, Gonghu Bay, Western Lake Taihu and Xukou Bay in a large, shallow, eutrophic freshwater lake (Lake Taihu, China). Water and surface sediment samples were collected at 35 sampling sites in January 2014 (winter) and July 2015 (summer). The physicochemical characterization showed that there were obvious changes in the trophic status and eutrophic index of five lake regions, which was mainly due to the difference of organic matter source. Based on the analysis of aquatic environmental characteristics, the organic nitrogen or nitrate nitrogen was the main storing form in the overlying water of five lake regions. In addition, nitrate nitrogen in pore water was lower than in overlying water, while ammonia nitrogen in pore water was higher than in overlying water. According to the DGGE profiles, temporal and spatial variations of bacterial community were apparent. Bacterial diversity was higher in summer than in winter and increased with the decrease in the lake region trophic status. The dendrogram of the bacterial community similarities revealed that samples were almost all grouped into two defined clusters (summer and winter), which indicated that season rather than region was the dominant factor. Canonical correspondence analysis demonstrated that ammonia nitrogen and nitrate–nitrite nitrogen in the sediment and pore water, organic matter and temperature significantly influenced the sediment bacterial community in the five lake regions.     

Climate‐related changes of soil characteristics affect bacterial community composition and function of high altitude and latitude lakes

Lakes at high altitude and latitude are typically unproductive ecosystems where external factors outweigh the relative importance of in‐lake processes, making them ideal sentinels of climate change. Climate change is inducing upward vegetation shifts at high altitude and latitude regions that translate into changes in the pools of soil organic matter. Upon mobilization, this allochthonous organic matter may rapidly alter the composition and function of lake bacterial communities. Here, we experimentally simulate this potential climate‐change effect by exposing bacterioplankton of two lakes located above the treeline, one in the Alps and one in the subarctic region, to soil organic matter from below and above the treeline. Changes in bacterial community composition, diversity and function were followed for 72 h. In the subarctic lake, soil organic matter from below the treeline reduced bulk and taxon‐specific phosphorus uptake, indicating that bacterial phosphorus limitation was alleviated compared to organic matter from above the treeline. These effects were less pronounced in the alpine lake, suggesting that soil properties (phosphorus and dissolved organic carbon availability) and water temperature further shaped the magnitude of response. The rapid bacterial succession observed in both lakes indicates that certain taxa directly benefited from soil sources. Accordingly, the substrate uptake profiles of initially rare bacteria (copiotrophs) indicated that they are one of the main actors cycling soil‐derived carbon and phosphorus. Our work suggests that climate‐induced changes in soil characteristics affect bacterioplankton community structure and function, and in turn, the cycling of carbon and phosphorus in high altitude and latitude aquatic ecosystems.     

Limnologic consequences of the decline in hemlock 4800 years ago in three Southern Ontario lakes

Four thousand eight hundred years ago hemlock (Tsuga canadensis) populations were decimated throughout eastern North America. We have studied the effects of this loss from the terrestrial community on three Southern Ontario lakes: Little Round Lake, Sunfish Lake, and McKay Lake. This study includes the use of cladocerans, diatoms, chrysophytes, and bacterial pigments to assess the limnologic changes that occurred in these lakes. Each lake experienced a change in trophic status that coincided with the loss of hemlock from its catchment, but the change in the aquatic biota was different in each lake. The lakes' size may have been the most influential factor governing the response to this terrestrial disturbance.     

Adaptations of microbial communities and dissolved organics to seasonal pressures in a mesotrophic coastal Mediterranean lake

In lake ecosystems, changes in eukaryotic and prokaryotic microbes and the concentration and availability of dissolved organic matter (DOM) produced within or supplied to the system by allochthonous sources are components that characterize complex processes in the microbial loop. We address seasonal changes of microbial communities and DOM in the largest Croatian lake, Vrana. This shallow lake is connected to the Adriatic Sea and is impacted by agricultural activity. Microbial community and DOM structure were driven by several environmental stressors, including drought, seawater intrusion and heavy precipitation events. Bacterial composition of different lifestyles (free-living and particle-associated) differed and only a part of the particle-associated bacteria correlated with microbial eukaryotes. Oscillations of cyanobacterial relative abundance along with chlorophyll a revealed a high primary production season characterized by increased levels of autochthonous DOM that promoted bacterial processes of organic matter degradation. From our results, we infer that in coastal freshwater lakes dependent on precipitation-evaporation balance, prolonged dry season coupled with heavy irrigation impact microbial communities at different trophic levels even if salinity increases only slightly and allochthonous DOM inputs decrease. These pressures, if applied more frequently or at higher concentrations, could have the potential to overturn the trophic state of the lake.     

Eutrophication as a driver of microbial community structure in lake sediments

Lake sediments are globally important carbon sinks. Although the fate of organic carbon in lake sediments depends significantly on microorganisms, only few studies have investigated controls on lake sedimentary microbial communities. Here we investigate the impact of anthropogenic eutrophication, which affects redox chemistry and organic matter (OM) sources in sediments, on microbial communities across five lakes in central Switzerland. Lipid biomarkers and distributions of microbial respiration reactions indicate strong increases in aquatic OM contributions and microbial activity with increasing trophic state. Across all lakes, 16S rRNA genes analyses indicate similar depth-dependent zonations at the phylum- and class-level that follow vertical distributions of OM sources and respiration reactions. Yet, there are notable differences, such as higher abundances of nitrifying Bacteria and Archaea in an oligotrophic lake. Furthermore, analyses at the order-level and below suggest that changes in OM sources due to eutrophication cause permanent changes in bacterial community structure. By contrast, archaeal communities are differentiated according to trophic state in recently deposited layers, but converge in older sediments deposited under different trophic regimes. Our study indicates an important role for trophic state in driving lacustrine sediment microbial communities and reveals fundamental differences in the temporal responses of sediment Bacteria and Archaea to eutrophication.     

Modelling the importance of sediment bacterial carbon for profundal macroinvertebrates along a lake nutrient gradient

In dimictic, temperate lakes little is known about the quantitative importance of trophic coupling between pelagic and profundal communities. Although it is a generally accepted paradigm that profundal secondary production is dependent on autochthonous pelagic production (primarily diatoms), the importance of interactions between phytodetrital inputs, sediment bacteria, and macroinvertebrates are still not well understood. In this study, we used theoretical models to estimate macroinvertebrate carbon requirement (production + respiration) and bacterial production for lakes of different trophic categories. Comparisons of estimates show that the importance of bacterial production as a carbon source for benthic macroinvertebrates is inversely related to lake trophic state. Assuming that infauna assimilates 50% of ingested bacterial carbon, this food source could account for between 47% (oligotrophic lakes) and 2% (hypertrophic lakes) of their carbon demand. These calculations indicate that bacterial carbon should not be an important C-resource for profundal macroinvertebrates of eutrophic and hypertrophic lakes.     

Microbial utilization of lipids in lake water

Abstract: This report evaluates the importance of lipids as a source of substrates for metabolism of heterotrophic bacteria based on measurements of uptake of [³H]palmitic acid and lipase activity in lakes of differing degrees of eutrophication. The highest rates of utilization of lipids by bacteria (i.e. specific and actual rates of uptake of [³H]palmitic acid and specific lipase activity) were observed in pelagic water of mesotrophic lake where the highest concentration and the shortest turnover time of natural pool of palmitic acid was found. Lipids in highly eutrophicated lakes were less important for metabolism of aquatic bacterial communities. Lipid content in lake water depended on species composition of plankton in the studied lakes.     

Structure and activity of lacustrine sediment bacteria involved in nutrient and iron cycles

Knowledge of the bacterial community structure in sediments is essential to better design restoration strategies for eutrophied lakes. In this regard, the aim of this study was to quantify the abundance and activity of bacteria involved in nutrient and iron cycling in sediments from four Azorean lakes with distinct trophic states (Verde, Azul, Furnas and Fogo). Inferred from quantitative PCR, bacteria performing anaerobic ammonia oxidation were the most abundant in the eutrophic lakes Verde, Azul and Furnas (4.5-16.6%), followed by nitrifying bacteria (0.8-13.0%), denitrifying bacteria (DNB) (0.5-6.8%), iron-reducing bacteria (0.2-1.4%) and phosphorus-accumulating organisms (<0.3%). In contrast, DNB dominated sediments from the oligo-mesotrophic lake Fogo (8.8%). Activity assays suggested that bacteria performing ammonia oxidation (aerobic and anaerobic), nitrite oxidation, heterothrophic nitrate reduction, iron reduction and biological phosphorus storage/release were present and active in all Azorean lake sediments. The present work also suggested that the activity of DNB might contribute to the release of phosphorus from sediments.     

Using aquatic macrophyte community indices to define the ecological status of European lakes

Defining the overall ecological status of lakes according to the Water Framework Directive (WFD) is to be partially based on the species composition of the aquatic macrophyte community. We tested three assessment methods to define the ecological status of the macrophyte community in response to a eutrophication pressure as reflected by total phosphorus concentrations in lake water. An absolute species richness, a trophic index (TI) and a lake trophic ranking (LTR) method were tested at Europe-wide, regional and national scales as well as by alkalinity category, using data from 1,147 lakes from 12 European states. Total phosphorus data were used to represent the trophic status of individual samples and were plotted against the calculated TI and LTR values. Additionally, the LTR method was tested in some individual lakes with a relatively long time series of monitoring data. The TI correlated well with total P in the Northern European lake types, whereas the relationship in the Central European lake types was less clear. The relationship between total P and light extinction is often very good in the Northern European lake types compared to the Central European lake types. This can be one of the reasons for a better agreement between the indices and eutrophication pressure in the Northern European lake types. The response of individual lakes to changes in the abiotic environment was sometimes represented incorrectly by the indices used, which is a cause of concern for the use of single indices in status assessments in practice.     

Similarity between contemporary vegetation and plant remains in the surface sediment in Mediterranean lakes

相似文献   

Resource Availability and Spatial Heterogeneity Control Bacterial Community Response to Nutrient Enrichment in Lakes

The diversity and composition of ecological communities often co-vary with ecosystem productivity. However, the relative importance of productivity, or resource abundance, versus the spatial distribution of resources in shaping those ecological patterns is not well understood, particularly for the bacterial communities that underlie most important ecosystem functions. Increasing ecosystem productivity in lakes has been shown to influence the composition and ecology of bacterial communities, but existing work has only evaluated the effect of increasing resource supply and not heterogeneity in how those resources are distributed. We quantified how bacterial communities varied with the trophic status of lakes and whether community responses differed in surface and deep habitats in response to heterogeneity in nutrient resources. Using ARISA fingerprinting, we found that bacterial communities were more abundant, richer, and more distinct among habitats as lake trophic state and vertical heterogeneity in nutrients increased, and that spatial resource variation produced habitat specific responses of bacteria in response to increased productivity. Furthermore, changes in communities in high nutrient lakes were not produced by turnover in community composition but from additional taxa augmenting core bacterial communities found in lower productivity lakes. These data suggests that bacterial community responses to nutrient enrichment in lakes vary spatially and are likely influenced disproportionately by rare taxa.