Production and enzymatic decomposition of organic matter by microplankton in a eutrophic lake

This report presents studies on temporal variations of phytoplankton and bacterioplankton production and the kinetics of bacterial enzyme activity (aminopeptidase, β-glucosidase and lipase) in the littoral and pelagial sampling sites of a highly eutrophic lake. Bacterial and algal production correlated well in pelagic water, but in the littoral there was no significant correlation between these processes. The highest activity of bacterial enzymes occurred during phytoplankton blooms (except β-glucosidase). The rates of enzymatic decomposition of organic matter in the littoral and pelagial sampling sites were similar. Turnover time of enzymatic hydrolysis of the studied biopolymers in lake water was the shortest for proteins and lipids during phytoplankton blooms in both sampling sites. The most dynamic changes in turnover time displayed were for the hydrolysis of polysaccharides by β-glucosidase in the littoral samples. The significance of organic matter for bacterial production and enzyme activity, and the role of enzymes in bacterial processing of biopolymers in a lake ecosystem are discussed