As bacterioplankton represent the largest living surface in the world`s oceans they play a central role in the
microbial loop. Up to now, bacteria have been treated as a "black box", neglecting differences in community
composition and therefore differences in the functional role of the different members of the group so far. New
molecular methods have made it possible to phylogenetically characterize species or distinct groups of prokaryotes.
Recently, we applied fluorogenic substances to concurrently assess hydrophilic and hydrophobic moieties of the
bacterial cell surface. An increase of the ratio between hydrophobic to hydrophilic moieties was detectable during
the exponential growth phase, while hydrophilicity inereased again in the stationary phase.
In this study we want to directly link baeterial groups using fluorescence in situ hybridisation (FISH) to certain
functions of the bacterial cell surface. First of all, bacterial community composition together with bacterial cell
surface charge should be monitored during an algal bloom. Additionally, the same parameters should be tested in
seawater dilution cultures incubated under different nutrient conditions. Finally, flow cytometry and capillary
electrophoresis will be tested as possible tools to asses hydrophobicity at sea during research cruises.
Specific attention should be paid to the role of nutrients influencing bacterial cell surface charge and bacterial
community composition.