Regulation of cellulases and xylanases from a derepressed mutant of Cellulomonas flavigena growing on sugar-cane bagasse in continuous culture

When the wild type Cellulomonas flavigena was grown on glycerol, xylose or cellobiose, it produced basal levels of carboxy-methyl-cellulase (CMCase), filter-paperase (FPase) and xylanase activities. By comparison, a catabolic derepressed mutant strain of the same organism produced markedly higher le vels of these enzymes when grown on the same carbon sources. Sugar-cane bag asse induced both the wild type and the mutant strain to produce three- to eight-time higher levels of FPase and xylanase than was observed with xylos e or cellobiose. Continuous culture was used to determine the minimal cello biose or glucose concentrations that repress the enzyme synthesis in both s trains. 2.5 g l(-1) glucose repressed FPase and xylanases from wild type, w hile 1.6 times more glucose was needed to repress the same activities in th e PN-120 strain. In the same way, twofold more cellobiose was needed to red uce by 75% the CMCase and xylanase activities in the mutant compared to the wild type. The FPase in the presence of 4 g l(-1) cellobiose did not chang e in the same strain. Therefore, its derepressed and feedback resistant cha racters of PN-120 mutant are evident. On the other hand, isoelectrofocused crude extracts of mutant and wild strains induced by sugar-cane bagasse, di d not show differences in protein patterns, however, the Schiffs staining w as more intense in the PN-120 than in the wild strain. These results point out that the mutational treatment did not apparently change the extracellul ar proteins from mutant PN-120 and this could affect their regulation sites , since derepressed and feed-back resistant enzymes may be produced. (C) 20 01 Elsevier Science Ltd. All rights reserved.