Bottom-up and top-down control of bacterial community composition in the euphotic zone of a reservoir

Abstract

Temporal changes in the bacterial community composition (BCC) and the impact of resources and predation on this community composition have been studied in the euphotic zone of the Sep reservoir (France), using terminal-restriction fragment length polymorphism (T-RFLP) and fluorescent in situ hybridization (FISH) for Eubacteria (EUB338) and eubacterial subgroups. Net growth and grazing rates of the various subgroups were computed from experiments conducted in dialysis bags in the presence or absence of predators. There was a significant difference between the grazing rates of different bacterial groups and subclasses, the alpha-proteobacteria (ALF1b) were subjected to the highest grazing rate (max. 1.76 d -1 ). In contrast, the beta-proteobacteria (BET42a) seemed to be little consumed by bacterivorous organisms, and predation led to large variations in the grazing rates of Cytophaga-Flavobacterium (CF319a). The different composition of bacterial consumers (Dinobryon sp. and Cladocera) during the study could explain the observed differences in grazing impact. The mean net growth rates of total bacteria, EUB338, BET42a ALF1b, and CF319a in dialysis bags without predators were 0.21, 0.69, 0.45, 0.50 and 0.84 d -1 , respectively. Various statistical analyses indicated that the BCC could depend on the organic matter excreted by the phytoplankton. There were also positive correlations not only between net growth and/or net production of ALF1b and CF319a with the primary production and biomass of the main phytoplankton groups, but also between phytoplankton biomass, primary production (PP) and some operational taxonomic units (OTUs). Among the physical variables, input and output of water in the reservoir seem to play a role in determining the BCC in this ecosystem. The results suggest that the BCC depends on the combined impact of dominant substrate sources and selective predation by bacterial consumers.

The power of species sorting: Local factors drive bacterial community composition over a wide range of spatial scales

“…This efficiency of space sorting is most likely due to the extremely high population growth rates of bacteria. Several studies that focused on the dynamics of BCCs in local habitats have indeed reported that bacterial communities can rapidly track changes in the environment (14,(27)(28)(29)(30)(31).…”

Spatio-temporal patterns of bacterioplankton production and community composition related to phytoplankton composition and protistan bacterivory in a dam reservoir

“…2imek et al 1998, Gasol et al 2002, Ma$ín et al 2003. For example, the spatially and temporarily variable role of protistan bacterivory and viral lysis has been reported for different parts of several canyon-shaped reservoirs and has shown a broad range of impacts of the 2 mortality factors on bacterioplankton production and community dynamics , Weinbauer et al 2003, Jardillier et al 2004.…”

“…2imek et al 1998, Gasol et al 2002, Ma$ín et al 2003. For example, the spatially and temporarily variable role of protistan bacterivory and viral lysis has been reported for different parts of several canyon-shaped reservoirs and has shown a broad range of impacts of the 2 mortality factors on bacterioplankton production and community dynamics , Weinbauer et al 2003, Jardillier et al 2004.Regarding bottom-up controlling factors, more pronounced gradients in microbial and phytoplankton variables are to be expected when the inflow river water parameters, particularly nutrients and organic matter loads, differ markedly from those in the lacustrine parts of a reservoir (Gasol et al 2002, Ma$ín et al 2003, 2imek et al 2005. The bottom-up factors constraining growth of various phylogenetic bacterioplankton groups in the canyon-shaped Ř ímov reservoir have been studied in short-term incubations in dialysis bags by transplanting water samples into reservoir areas that were differently resource-limited , 2imek et al 2005).…”

Successional changes in bacterial community assemblages following anoxia in the hypolimnion of a eutrophic lake

“…Water samples of 400 ml were filtered onto 0.2 µm pore-size polycarbonate filters (47 mm diameter, GTTP, Millipore). DNA extractions were performed as described in Jardillier et al (2004). For T-RFLP analysis, amplification of the bacterial 16S rDNA genes was performed using a combination of the bacterial 5'-FAM-labeled 27f primer and the universal primer 1492r (Table 1).…”