INVESTIGATION ON THE INTERACTION OF CELLOBIOSE DEHYDROGENASE AND CELLULASE IN THE DEGRADATION OF CELLULOSE BY Fusarium oxysporum

Abstract

Ten fungal isolates were screened for the production of cellulase and cellobiose dehydrogenase (CDH). Among the screened isolates; Fusarium oxysporum gave the highest yield of the enzymes and was selected for further studies. Fusarium oxysporum was grown on four commercial cellulosic substrates- avicel, α-cellulose, methyl-cellulose and sodium carboxy-methyl cellulose for enzyme production and biodegradation studies. Methyl cellulose supported the cooperative production of cellulase and CDH with specific activities of 130.33 U/mg and 195 U/mg, respectively at the 96th hour of biodegradation. A cooperation was observed with the enzymes with maximum production obtained at pH 6.0. Similarly, maximum yield of glucose (2.12 μmol/ml) was obtained at pH 6.0. A decline in production of cellulase and CDH was obtained as the pH increased above 6.0. Mn2+, Zn2+, Fe2+ and Ca2+ enhanced the biodegradation of methyl cellulose with an increase in the glucose liberated during the process and there was an increase in production of enzymes in a cooperative manner. Repression of CDH by Co2+ and Mg2+ affected the biodegradation adversely with low yield of glucose. The increase in glucose shows progress in cellulose biodegradation. Cellulase and CDH from Fusarium oxysporum were stable over pH 5.0 – 7.0 with about 60% residual activity after 90 minutes of incubation. Similarly, they showed moderate thermostability over 40 – 60oC. Their activities were enhanced in the presence of 5 mM and 10 mM Mn2+ and Ca2+. The result from the study revealed the interaction of cellulase and CDH is cooperative in degradation of cellulose. This finding is important for metabolites production and biofuel generation from cellulosic biomasses.