A continuous culture study of the regulation of extracellular protease production in Vibrio SA1

Abstract

During growth of Vibrio SA1 in a lactate-limited chemostate in the presence of 2mM phenylalanine as an inducer, the rate of production of two proteolytic enzymes, namely an endopeptidase and an aminopeptidase, was dependent upon the dilution rate. An optimum in the rate of synthesis of both proteases was observed at a dilution rate of 0.23 h-1 and enzyme production only occurred between dilution rates of 0.06 and 0.45 h-1. Without inducer a low rate of aminopeptidase production was found with an optimum at 0.19 h-1, but only trace amounts of endopeptidase were detectable in the culture. In the presence of inducer the rate of enzyme production increased with increasing dilution rates over the range 0.06 to 0.23 h-1 which was explained by an increase in saturation of inducer sites. The progressive decrease in the rate of protease production at higher dilution rates was ascribed to an increasing effect of catabolite repression by the increasing concentration of the growth substrate. It was shown that 5 mM cyclic AMP could not relieve catabolite repression caused by glucose or lactate. Repression of protease production also occurred in the presence of higher concentrations (5 mM) phenylalanine and other amino acids and by ammonium ions. It is suggested that the energy-status of the cell may play an important role in the regulation of protease synthesis in Vibrio SA1.