Temporal and spatial variation of bacterioplankton subgroups

Research project P 14387 Temporal and spatial variation of bacterioplankton subgroups Roland PSENNER 26.6.2000 Heterotrophic bacterioplankton is a complex community, which is exposed to many different environmental factors. Investigations of natural bacterial assemblages should therefore be able to yield a detailed image of the bacterial properties at adequate temporal and spatial resolution and to link patterns of bacterial activity to short- term environmental changes. However, this ideal is often heavily compromised by technical constraints. Flow cytometry seems to be a promising tool by which several of the limitations encountered in ecological studies can be circumvented. Since the installation of a two-laser instrument at our lab in January 1999, intensive investigations of bacterial communities from lakes, biofilms and chemostat experiments have been carried out. The instrument has proven highly effective in the quantification of bacteria and the measurement of fluorescence signals from specific stains. Furthermore, subgroups of the bacterial community could be sorted for microscopic validation. The application of specific stains to quantify cellular compounds such as nucleic acids or proteins showed that natural bacterial communities typically fall into several discrete subgroups rather than showing a continuum of fluorescence over the observable range. Analysis must obviously focus on these bacterial subgroups in order to achieve more detailed information on natural bacterial assemblages. Furthermore, this can be the key to link bacterial data from flow cytometry to environmental conditions, thus greatly enhancing the value of flow cytometers in ecological investigations. In this project we propose to study bacterial subgroups as detected by flow cytometry with two approaches: The first study will focus on the diel cycles of the bacterial community at high temporal resolution. Complementary, we will investigate fine-scale vertical distribution of bacterial subgroups at different times of the year. By this dual approach, we expect to gain a better understanding of the bacterioplankton`s structure and the driving forces behind its changes.