Stachybotrys microspora is a filamentous fungus characterized by the secretion of multiple b-glucosidases. The production of these enzymes was studied under culture with variable carbon sources. The highest activity was produced on glucose (0.66 U ml -1 ) whereas galactose, lactose, cellobiose, Avicel cellulose, carboxymethylcellulose (CMC), wheat bran and gruel allowed intermediate production levels ranging between 0.08 and 0.48 U ml -1 . The zymogram analysis showed that complex sugars such as Avicel cellulose and CMC induced the expression of several b-glucosidases whereas all tested simple sugars (mono and disaccharides) induced the expression of one single b-glucosidase, each time different. The most efficient b-glucosidase named bglG was produced on glucose which continues to be, at the same time, its strong inhibitor. The bglG N-terminal sequence confirmed that it is a novel b-glucosidase. According to its large molecular weight, this enzyme was assumed to belong to family 3 of b-glucosidases. RT-PCR analysis showed that family 3 expressions were induced on glucose while those of family 1 were repressed. Finally, with the use of different combinations of glucose and various carbon sources at different ratio, we showed that such sources direct the differential expression of b-glucosidases in S. microspora since our strain co-produced the b-glucosidases corresponding to each carbon source.
The production profile of cellulases of the mutant strain A19 from the filamentous fungus Stachybotrys microspora was studied in the presence of various carbon sources (glucose, lactose, cellulose, carboxymethylcellulose (CMC), and wheat bran) and a range of medium initial pH (5, 7, and 8). Two extracellular cellulases from the Stachybotrys strain (endoglucanases and β-glucosidases) were monitored by enzymatic assay, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and zymogram analysis. Glucose and lactose repressed CMCase time course production while they permitted a strong β-glucosidase one. On Avicel cellulose, CMC, and wheat bran, both activities were highly produced. Wheat bran (WB) is the best carbon source with an optimum of production at days 5 and 6. The production kinetics of both activities were shown to depend on the medium initial pH, with a preference for neutral or alkaline pH in the majority of conditions. The exception concerned the β-glucosidase which was much more produced at acidic pH, on glucose and cellulose. Most interestingly, a constitutive and conditional expression of an alkaline endoglucanase was revealed on the glucose-based medium at an initial pH of 8 units. The zymogram analysis confirmed such conclusions and highlighted that carbon sources and the pH of the culture medium directed a differential induction of various endoglucanases and β-glucosidases.
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