We investigated the linkages between the composition and the activities of bacterio-plankton assemblages in the meso-eutrophic Rimov reservoir (Czech Republic). We examined bacterial fractions with visible leucine and glucose incorporation using microautoradiography, and proportions of bacteria with an intact membrane (live), high nucleic acid (HNA) and low nucleic acid (LNA) content, and an active electron transport system (CTC+ cells; CTC is 5-cyano-2,3-ditolyl-tetrazolium chloride) by flow cytometry. Three stations along the longitudinal axis of the reservoir (designated Dam, Middle, and River) with contrasting phosphorus concentrations and bacterial and extracellular phytoplankton production were sampled at intervals of 3 wk from 29 March to 15 November 2005. At all stations, Betaproteobacteria (BET) or Actinobacteria (ACT) dominated the bacterial community composition, while Cytophaga-Flavobacteria (CF) accounted for smaller proportions. ACT showed high proportions of cells incorporating both leucine and glucose in all samples, whereas only small fractions of CF were scored positive for the incorporation of these substrates. BET incorporated leucine preferentially to glucose in all samples. We identified bacterial phylogenetic groups that correlated with different bacterial populations as determined by flow cytometry: CF and BET significantly contributed to the pool of HNA cells at Stn River, whereas the opposite was found for ACT, forming the pool of LNA cells at all stations. Since ACT efficiently incorporated organic substrates, the LNA fraction represented a highly active component of bacterial assemblages. At Stns Dam and Middle, the dynamics of CF also correlated with the population of CTC+ cells and an enhanced extracellular phytoplankton production.
