Enzymes as river pollutants and the response of native epilithic extracellular-enzyme activity

Extracellular-enzyme activity was measured in three watercourses, in North East England, which received effluent from sewage-works. beta-D-glucosidase, leucine-aminopeptidase and phosphatase activities were markedly elevated in water downstream of outfalls. Despite subsequent downstream decrease, elevated activities persisted over several kilometres. Thus the effluents not only increased the quantity of organic matter in the rivers, they also increased enzymatic hydrolysis of polymeric compounds, thus increasing the supply of low-molecular-weight moieties available for microbial uptake and hence facilitating biopurification. Partitioning of river water, by 0.2 microm filtration, showed that free-enzyme activity was important as well as cell and particle-associated activity. Extracellular-enzyme activity was measured on stones from the bed of one watercourse. There was no evidence of end-product repression of native epilithic enzyme activity, even though enzyme activity in surrounding water was very high. Instead, beta-D-glucosidase and phosphatase activity increased on stones downstream of the outfall, and this was accompanied by an increase in the percentage of culturable epilithic bacteria capable of synthesizing extracellular beta-D-glucosidase and phosphatase.