Protein hypersecretory Trichoderma reesei mutant RUT C-30 displays increased ethanol and polyene resistance

Abstract

Addition of low amounts of ethanol (0.5–2%, v/v) or of polyene antibiotics (nystatine, amphotericin B 0.5–2 mg l −1, respectively) to cultures of T. reesei QM 9414 in the early phase of mycelial growth, arrested the secretion of three cellulases (cellobiohydrolase I and II, endoglucanase I) as well as of a xylanase. Enzyme formation by the enzyme-hyperproducing strain T. reesei RUT C-30, in contrast, was less sensitive to these agents. By the use of [U- 14C]- l-valine addition, this blockage of enzyme formation was shown to be due to a general inhibition of protein secretion by ethanol. Ethanol and amphotericin B also arrested the formation of intracellular precursers of cellobiohydrolase I, and the formation of the cbh1-mRNA, hence proving that blockage occurs at a pre-translational level. The higher sensitivity of the lower producing mutant T. reesei QM 9414 correlated with an increased synthesis of a 36 kDa stress protein. The data are discussed with respect to a plasma membrane located resistance to ethanol or polyenes in the hyperproducing mutant T. reesei RUT C-30, probably caused by the use of bile acids as colony restrictor in the course of mutant selection.