Isolation and Characterization of a Mutant of Trichoderma reesei Showing Reduced Levels of Extracellular  -Glucosidase

Abstract

A mutant (D6-1 3 ) of Trichoderma reesei that produced low levels of extracellular /?-glucosidase was physiologically and biochemically characterized. The mutant was unable to grow and produced very little cellulase activity on Solka-Floc, Avicel, micro-crystalline cellulose and acidswollen cellulose. Whereas growth was nearly normal on cellobiose, lactose and glucose, cellulase production was slightly decreased on cellobiose and lactose. The mutant produced nearly normal levels of FPA (filter-paper activity) and endoglucanase on sophorose. A distinct lag and a lowered specific sugar consumption rate was observed for the mutant on 0.3% cellobiose; this appeared to be due to lowered wall-bound /?-glucosidase activity. The multiplicity and role of different P-glucosidases in T. reesei is discussed. I N T R O D U C T I O NThe cellulase and /?-glucosidase systems from Trichoderma reesei have been extensively studied to understand the mechanism of cellulase induction by cellulose (Merivuori et al., 1984;Kubicek, 1987;Kubicek et al., 1988). The cellulase enzymes are inducible by cellulose, cellobiose, cellobionolactone, lactose and sophorose (Sternberg & Mandels, 1979Bruchmann et al., 1987), whereas glucose and glycerol are repressors of cellulase biosynthesis (Montenecourt & Eveleigh, 1979). Since cellulose is insoluble it has been suggested that the true inducer may be sophorose, resulting from the degradation of cellulose by the combined action of endoglucanase and P-glucosidase (Gritzali & Brown, 1979; Vaheri et al., 1979a,b). In T. reesei inhi bit ion of plasma-membrane-bound P-glucosidase by nojirimycin and glucono-b-lactone prevents endoglucanase induction by cello-oligosaccharides but not by sophorose, implicating /?-glucosidase in de novo cellulase induction (Kubicek, 1987).Direct evidence for the role of P-glucosidase in cellulase induction would be provided by the characteristics of T. reesei mutants negative for or low in /?-glucosidase production. This paper contains the first report of the isolation of a mutant of T. reesei low in extracellular /?-glucosidase production. The mutant was physiologically and biochemically characterized in terms of its ability to grow and to produce cellulases on insoluble and soluble cellulase inducers. The presence of P-glucosidases in other subcellular fractions was also investigated to understand the origin and multiplicity of the enzyme. METHODSOrganism and isolation of mutant. Trichoderma reesei D-1/6 (Ghose et al., 1982) was the parent strain. The low+ glucosidase mutant D6-13 used in this study was isolated as a routine auxotrophic mutant from D-1/6 using the UV-irradiation method described for isolation of amino acid auxotrophs in T. reesei by Toyama et al. (1984). The rate of survival of treated conidia was 1 %. D6-13 is a lysine-requiring auxotroph.

Population diversity and genomics of the fungal pathogen of canola Leptosphaeria maculans

“…The study found that although the absence of bgl1 caused delayed induction of cellulase enzymes, it had no effect on growth or mRNA production abilities of the cell. However, other gene disruption studies on β-glucosidase genes produced different results (Mishra et al, 1989;Strauss and Kubicek, 1990), leading us to believe that specific functional analysis of this gene in L. maculans is required.…”