Bacterial enzyme activities in ground water during bank filtration of lake water

Abstract

The interactions between organic matter, bacterial biomass, enzyme activities and environmental factors were studied during bank filtration of humus-rich lake water. The exoenzymatic β-glucosidase, phosphatase and alanine-aminopeptidase activities in water were measured in vitro as release of fluorescing degradation products from methylumbelliferyl substrates. The total enzymatic decomposition activity was mesured as the hydrolysis of fluorescein diacetate (FDA). Bacterial enzymatic activities decreased strongly after infiltration of lake water. The decrease in the enzyme activities correlated with decrease in bacterial counts and biomass production. However, the increase in specific FDA-hydrolysis activity (activity per bacterial cell) indicated that maintenance energy requirements increased during filtration in the ground. There was also an increase in the specific phosphatase activity, which might be associated with the decrease in the concentration of available phosphate. All enzyme activities depended on seasonal temperature changes. The highest FDA-hydrolysis, phosphatase and β-glucosidase activities occurred during the summer months, when the bacterial production activity and the demand of essential nutrients were highest. On the contrary, the alanine-aminopeptidase activity was highest during autumn and winter, probably as a result of infiltrated nitrogenous material from senescing and dying microbes and algae in lake water. The close correlations between enzymatic activities and other microbial parameters suggest that enzyme activities can be used to monitor the changes in microbiological quality of water during bank filtration of lake water.