The effects of sewage-works effluent on riverine extracellular aminopeptidase activity and microbial leucine assimilation

Extracellular aminopeptidase activity and microbial leucine assimilation, both processes related to protein degradation and biopurification of organic pollutants, were investigated in relation to sewage-works discharges. The rivers studied were the Swale, and its tributary the Wiske in which there was less dilution of effluent. Localized increase in planktonic leucine aminopeptidase activity and leucine assimilation, associated with increased bacterioplankton abundance, potentially enhanced biopurification in both rivers. In contrast, epilithic leucine aminopeptidase activity was not consistently elevated in response to discharges. Epilithic leucine assimilation and bacterial abundance did, however, tend to increase; this response might have favoured biopurification, despite the lack of enhanced aminopeptidase activity. General downstream increase in aminopeptidase activity and amino-acid assimilation, previously described along the Swale, was shown not to be a simple response to successive sewage-works discharges.