Effect of carbon sources on cellulase production by clostridium cellulolyticum

Abstract

The effect of varying carbon source on cellulase activity in C. cellulolyticum has been investigated using a basal culture medium supplemented with various compounds, including Avicel which gave the best results indicating that both the production of cellulase components (FPAse, CMCase, PNPGase and xylanase) and the bacterial hydrolysis yield increase with the degree of crystallinity. Glucose and cellobiose alternative products of cellulolysis, had contrasting effects. At concentrations from 0.5 to 5 mM when mixed with Avicel glucose enhances, while cellobiose inhibits, the production of cellulase. In contrast, in the absence of Avicel, cellobiose has a greater effect in enhancing cellulase production than glucose. At 7.5 g.l −1 other sugars (fructose, xylose and arabinose) are also more effective than cellobiose in promoting cellulase production. Glucose, in contrast to cellobiose, has a greater effect on derepression of Avicelase and inhibits neither Avicelase activity in solution nor bacterial cellulolysis in solid culture media. Cultures grown in a fermenter, using either sugar, show that growth inhibition can be lowered and production greatly improved. The best results were obtained under conditions of cellobiose limitation using ultrafiltration to the growth inhibiting metabolites. Culture carboxymethylcellulose (CMC), a soluble cellulose derivative, causes both immediate growth and a rapid production of CMCase, PNGase and xylanase activities whereas the capacity to hydrolyse cellulose of filter paper (FPase) is absent. The sugars released during cellulolysis inhibit both cell growth and cellulase production indicating that C. cellulolyticum produces a “true cellulase system” subject to end-product regulation.