Changes In the bacterioplankton community of oligotrophic Lake Stechlin (northeastern Germany) after humic matter addition

Abstract

In an effort to better understand the dynamics of members of the bacterioplankton community in relation to humic matter (HM) addition, and to provide insight into the ecology of common and persistent as well as transient freshwater bacteria, we designed a study with a batch and a dilution approach. We used single vs. repeated HM additions in incubations with bacterial communities from the epilimnion (0-10 m) and hypolimnion (40 m) of oligotrophic Lake Stechlin (northeastern Germany). Molecular methods were applied for detailed phylogenetic characterization of bacterial community composition (BCC) every 2 wk over 8 wk of incubation at in situ temperature. Whereas no significant differences in the development of BCC in batch vs. dilution cultures were observed, the BCC of epilimnic and hypolimnic samples greatly differed. This indicates that HM addition led to the establishment of a highly specific but different BCC depending on the source community in combination with the respective in situ temperature. Further, DGGE banding patterns revealed a high variability in the BCC of epilimnic and hypolimnic samples. Betaproteobacteria were consistently present and specific Alphaproteobacteria, such as members of the Roseisalinus group, Bacteroidetes, and Deltaproteobacteria were enriched only after HM addition. Other phylogenetic groups, including Actinobacteria and Gammaproteobacteria, were only sporadically present. Our approach resulted in the cultivation of a variety of bacteria such as Lysobacter, Methylobacterium, Pseudomonas, Rhodopila, and Variovorax species. The addition of HM selected for specific HM-degrading bacterial phylotypes, which are found at different depths even in the clear waters of Lake Stechlin. © Inter-Research 2009 .