Numerical analysis of planktonic and reed biofilm bacterial communities of Lake Fertő (Neusiedlersee, Hungary/Austria)

Although heterotrophic bacterial populations are of utmost importance in the self-purification and detoxification processes of aquatic ecosystems, there are insufficient data available on the composition and activities of these microbial communities. Due to these facts water bacteriological studies concentrate more on the detailed species level analyses of complex bacterial communities. At the same time by investigating many biochemical properties of the strains, one can get information on their possible activities and interrelations. In order to have a more complete understanding of bacteria living in the Neusiedlersee (Lake Fertő), a shallow, turbid, mesotrophic lake, 296 bacterial strains were subjected to morphological and detailed physiological–biochemical studies. They were determined at least at generic level. The predominant members of the bacterioplankton were aerobic respiratory organisms. A great number of the isolated strains could tolerate high salt concentrations, grew at high pH values and were mostly inactive in their degradation capabilities. A wide variety of taxa proved to be present in open waters, the predominant ones, the members of the genera Micrococcus, Pseudomonas and the Flavobacterium-Cytophaga group were almost in equal proportions. The distribution of bacteria widely varied among sampling regions. Compared with the Lake Balaton, where cocci dominate in the open water microbiota, the continuous presence of Gram-negative rods refers here to the continuous relatively high suspended solids content of the water. The reed epiphytic bacterial communities seem to be less diverse at species level and coryneforms seem to be in dominant position. Open water species diversity seems to be depended on the suspended solid content, whereas on the contrary in reed biofilms lower suspended solid values help to build up higher species diversity.