BACTERIAL LIPOLYTIC-ACTIVITY IN AN EUTROPHIC LAKE

The kinetics of lipase and distribution of enzyme activity was examine d in pelagial and littoral zone and the water column of an eutrophic l ake. Bacteria were major producers of lipase activity in lake water. A bout 15 % of the total activity of lipase in lake water was found in c ell-free, 0.2-mum filtrate. The V(max) of lipase activity varied marke dly in both sampling sites throughout the study period. Highest V(max) were measured in pelagial (754 nmol L-1 h-1) and in littoral (429 nmo l L-1 h-1) samples during spring phytoplankton development in April. V ery low V(max) (53 nmol L-1 h-1) was found in littoral in May. The Mic haelis constants (K(m)) of substrate hydrolysis by lipase in lake wate r ranged between 12-51 mumol/L (littoral) and from 21 to 78 mumol/L (p elagial). High K(m) values were determined in May, during clear water phase in pelagial (78 mumol/L), and in July (57 and 51 mumol/L in pela gial and littoral, respectively) during summer stratification of the l ake. The highest lipase activity was found in samples incubated at pH 7.5, i.e., close to natural pH (7.8) of lake water. Lipase activities of samples decreased when incubated at pH lower and/or higher than 7.5 . Various organic compounds, which are bacterial substrates naturally present in lake water, influenced kinetic parameters (K(m) and V(max)) of lipase in lake water. Palmitic acid induced synthesis of the enzym e in bacteria.