Glucose feedback inhibition of amylase activity in Aspergillus sp. and release of this inhibition when cocultured with Saccharomyces cerevisiae

Abstract

The effect of starch and glucose concentration on amylase activity produced by Aspergillus niger, A. foetidus and A. awamori was determined. Up to 15 U ml-1 of amylase activity was observed in extracellular fluid of cultures grown with 1-2% starch for 7 days; however, no amylase activity was detectable in the extracellular fluid of otherwise identical cultures grown with 3-5% starch, even though these cultures contained substantial concentrations of glucose (16-20 mg ml-1) which could only have been derived from starch hydrolysis. When extracellular fluid from the 5% starch cultures was dialysed to remove soluble sugar, high level of amylase activity was observed. Addition of increasing amounts of glucose to the dialysed extracellular fluid resulted in increasing levels of inhibition of amylase activity. Coculture of the Aspergillus species with Saccharomyces cerevisiae, an efficient sugar fermenting yeast, in 5% starch medium resulted in low sugar concentration and high amylase activity (>18 U ml-1) in the extracellular fluid. Amylase activity in cultures grown with glucose was comparable to that observed in cultures grown with glucose plus starch or starch only. These results lead us to conclude that amylase activity in the Aspergillus species studied is subject to feedback inhibition by glucose but is not subject to catabolite repression by glucose or starch as previously believed. Furthermore, the amylase activity in these organisms appears to be inducible by starch. © 1986.