Medium Initial pH and Carbon Source Stimulate Differential Alkaline Cellulase Time Course Production in Stachybotrys microspora

Abstract

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.