The impact of a single-nucleotide mutation of bgl2 on cellulase induction in a XXXX mutant.

@entity8869 @entity8692 @entity505 @entity3689 @entity413
BACKGROUND: The filamentous fungus @entity8869 (anamorph of @entity8869 ) produces increased cellulase expression when grown on cellulose or its derivatives as a sole @entity505 source. It has been believed that b-glucosidases of @entity8869 not only metabolize @entity8692 but also contribute in the production of inducers of cellulase gene expression by their transglycosylation activity. The cellulase hyper-producing mutant PC-3-7 developed in Japan has enhanced cellulase production ability when @entity8692 is used as the inducer. The comparative genomics analysis of PC-3-7 and its parent revealed a single-nucleotide mutation within the bgl2 gene encoding intracellular b-glucosidase II (BGLII/Cel1a), giving rise to an @entity3689 substitution in PC-3-7, which could potentially account for the enhanced cellulase expression when these strains are cultivated on cellulose and @entity8692 . RESULTS: To analyze the effects of the BGLII mutation in cellulase induction, we constructed both a bgl2 revertant and a disruptant. Enzymatic analysis of the transformant lysates showed that the strain expressing mutant BGLII exhibited weakened @entity8692 hydrolytic activity, but produced some transglycosylation products, suggesting that the SNP in bgl2 strongly diminished cellobiase activity, but did not result in complete loss of function of BGLII. The analysis of the recombinant BGLII revealed that transglycosylation products might be oligosaccharides, composed probably of @entity413 linked b-1,4, b-1,3, or a mixture of both. PC-3-7 revertants of bgl2 exhibited reduced expression and inducibility of cellulase during growth on cellulose and @entity8692 substrates. Furthermore, the effect of this bgl2 mutation was reproduced in the common strain QM9414 in which the transformants showed cellulase production comparable to that of PC-3-7. CONCLUSION: We conclude that BGLII plays an important role in cellulase induction in @entity8869 and that the bgl2 mutation in PC-3-7 brought about enhanced cellulase expression on @entity8692 . The results of the investigation using PC-3-7 suggested that other mutation(s) in PC-3-7 could also contribute to cellulase induction. Further investigation is essential to unravel the mechanism responsible for cellulase induction in @entity8869 .
