Response of Marine Bacterioplankton to Experimental Manipulations of Growth Conditions

Coastal prokaryotic picoplankton is exposed to a highly variable environment. In this thesis the full cycle 16S rRNA approach for a cultivation-independent analysis of prokaryotic communities was applied to monitor and investigate the fate of bacterial populations in experimental incubations in the context of changes of potentially causative ecological factors. Altogether, the results presented here allowed a description of distinct opportunistic growth patterns of bacterial populations as responses to changes of ecological factors. The abundance and composition of Rhodobacteraceae populations significantly depended on the presence of exudates of phytoplankton. Alteromonadaceae/Colwelliaceae (A/C) responded instantaneously with growth to disturbances of the organic matter field. However, their high sensitivity to grazing by HNF resulted only in short-lived phases of dominance. Thus, A/C potentially might play an important role in the channeling of organic substrates within the microbial loop.