Seasonal dynamics and phylogenetic diversity of free-living and particle-associated bacterial communities in four lakes in northeastern Germany

Abstract

The phylogenetic diversity and seasonal dynamics of free-living and particle-associated bacterial communities were investigated in the epilimnion of 4 lakes of the Mecklenburg Lake Dis- trict, northeastern Germany. All lakes differed in their limnological features, ranging from olig- otrophic to eutrophic and dystrophic. Bacterial community structure and seasonal dynamics were analyzed by denaturing gradient gel electrophoresis (DGGE) and clone libraries of 16S rRNA gene fragments. Communities of free-living and particle-associated bacteria greatly differed among the lakes. In addition, significant differences occurred between both bacterial fractions within each lake. Seasonal changes were more pronounced in free-living than in particle-associated bacterial commu- nities. Non-metric multidimensional scaling (NMDS) analyses revealed several strong correlations between bacterial communities (both free-living and particle-associated) and environmental vari- ables such as pH, dissolved organic carbon (DOC), phytoplankton biomasses, and primary produc- tion. Phylogenetically, all cloned and sequenced 16S rRNA gene fragments belonged to already known freshwater clusters. Clone libraries of free-living bacteria were dominated by sequences of Actinobacteria, Bacteroidetes, and Betaproteobacteria, whereas those of particle-associated bacteria predominantly consisted of Cyanobacteria and Bacteroidetes sequences. Other freshwater phyla such as Alpha- and Gammaproteobacteria, Verrucomicrobia, Planctomycetes, and members of Can- didate Division OP10 were found in low proportions. These differences may indicate an adaptation of distinct bacterioplankton communities to the respective environmental conditions of each lake.