The composition of basal and induced cellulase systems in Penicillium decumbens under induction or repression conditions

Differences in the composition and expression of basal cellulase versus induced cellulase in Penicillium decumbens were investigated at the transcriptional and translational levels. Basal cellulase was composed of endoglucanase, cellobiohydrolase and β-glucosidase based on zymogram analysis following polyacrylamide gel electrophoresis. The pattern of activity for both β-glucosidase and cellobiohydrolase was the same under induction and repression conditions. However, the pattern of expression for the endoglucanases was different, and the induced endoglucanases were synthesized only under induction condition. The basal endoglucanase contained four components with molecular weights of about 43, 39, 36 and 34 kDa, and the 34-kDa protein (deduced as EG V) was the first basal endoglucanase to be expressed. A comparison of two purified endoglucanases with molecular weights of 34 kDa (basal cellulase) and 45 kDa (induced cellulase), revealed that basal and induced endoglucanases were encoded by different genes. Transcripts of the main cellulase genes cbh1, cbh2, egl1, egl2 and bgl1 were detected in P. decumbens cells grown with glucose or cellulose, whereas the transcriptional levels of the five cellulase genes and especially that of cbh1 and egl1 were lower under glucose-repression conditions. Combining the results of transcriptional analysis and activities staining, it can be concluded that the main cellulase genes of P. decumbens were transcribed at low basal levels. Both β-glucosidase and cellobiohydrolase transcripts were translated, but only a subset of the endoglucanase transcripts was translated and then the proteins were secreted from the cells, and these proteins comprised the real basal endoglucanases.