Structural and functional microbial diversity along a eutrophication gradient of interconnected lakes undergoing anthropopressure.

We present the results of an analysis of the 16S rRNA-based taxonomical structure of bacteria together with an analysis of carbon source utilization ability using EcoPlate (Biolog, USA) metabolic fingerprinting assessment against the backdrop of physicochemical parameters in fifteen interconnected lakes. The lakes exhibit a wide spectrum of trophic gradients and undergo different intensities of anthropopressure. Sequences of V3-V4 16S rRNA genes binned by taxonomic assignment to family indicated that bacterial communities in the highly eutrophicated lakes were distinctly different from the bacterial communities in the meso-eutrophic lakes (ANOSIM r = 0.99, p = 0.0002) and were characterized by higher richness and more diverse taxonomical structure. Representatives of the Actinobacteria, Proteobacteria, Cyanobacteria, Planctomycetes, Verrucomicrobia, Bacteroides phyla predominated. In most cases their relative abundance was significantly correlated with lake trophic state. We found no similar clear relationship of community-level physiological profiling with lake trophic state. However, we found some significant links between the taxonomic and metabolic structure of the microbes in the studied lakes (Mantel's correlation r = 0.22, p = 0.006). The carbon source utilization ability of the studied microorganisms was affected not only by the taxonomic groups present in the lakes but also by various characteristics like a high PO43- concentration inhibiting the utilization of phosphorylated carbon.

Quantitative description of respiration processes in meso-eutrophic and eutrophic freshwater environments.

We propose a modification of measurement methodology allowing the overall respiration rate (VResp) close to the in situ conditions; size of the labile, respirable organic matter pool (OMResp); and its turnover time (Tt) to be calculated. In addition to the respiration of dissolved substrates by free-living bacteria, the respiration of attached bacteria and other planktonic organisms is also taken into account. In case study we evaluated the modified, quantitative description of respiration processes in surface waters of lakes of different trophic status: mezzo-eutrophic and eutrophic. In both types of studied environments, VResp oscillated between 1.0 µmol C l-1 h-1 and 3.0 µmol C l-1 h-1, and the size of the OMResp pool varied from 39.3 µM C to 828.7 µM C. Despite of higher OMResp concentrations in eutrophic lakes, we found a lower susceptibility of OM to respiration processes in eutrophic than in meso-eutrophic lakes but similar VResp in both types of lakes. We conclude that the proposed method allows a fast quantitative description of labile organic matter utilization by aerobic aquatic microorganisms.

Predicting blooms of toxic cyanobacteria in eutrophic lakes with diverse cyanobacterial communities.

We investigated possibility of predicting whether blooms, if they occur, would be formed of microcystin-producing cyanobacteria. DGGE analysis of 16S-ITS and mcyA genes revealed that only Planktothrix and Microcystis possessed mcy-genes and Planktothrix was the main microcystin producer. qPCR analysis revealed that the proportion of cells with mcy-genes in Planktothrix populations was almost 100%. Microcystin concentration correlated with the number of potentially toxic and total Planktothrix cells and the proportion of Planktothrix within all cyanobacteria, but not with the proportion of cells with mcy-genes in total Planktothrix. The share of Microcystis cells with mcy-genes was low and variable in time. Neither the number of mcy-possessing cells, nor the proportion of these cells in total Microcystis, correlated with the concentration of microcystins. This suggests that it is possible to predict whether the bloom in the Masurian Lakes will be toxic based on Planktothrix occurrence. Two species of toxin producing Planktothrix, P. agardhii and P. rubescens, were identified by phylogenetic analysis of 16S-ITS. Based on morphological and ecological features, the toxic Planktothrix was identified as P. agardhii. However, the very high proportion of cells with mcy-genes suggests P. rubescens. Our study reveals the need of universal primers for mcyA genes from environment.