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Abstract

The community structure of bacterioplankton was examined by the direct analysis of low-molecular-weight (LMW) RNA (5S rRNA and tRNAs). This approach allows determination of the taxonomic structure of natural microbial communities to the species or genus level, without the inherent bias of all culture-dependent identification methods. Using high resolution electrophoresis of all low molecular RNAs, relative changes in the microbial community structure were monitored in a set of lake water mesocosm experiments. In these mesocosm experiments the impact of a large-scale release of test bacteria (Escherichia coli, Pseudomonas putida) and their culture medium on the indigenous bacterioplankton community was studied. The dynamics of the bacterioplankton community as determined by LMW RNA analysis indicated a very fast response (after 24h) to the nutrient addition but no significant effects were detected by the massive release of the test bacteria.