Abstract:
Five white rot fungal isolates obtained from a decaying wood were screened for their ability to degrade some lignocellulosic biomasses and produce extracellular hydrolytic and oxidative enzymes involved in the degradation process. Sporothrix carnis gave the highest yield of lignocellulolytic enzymes when grown on corn cob over 10 days of fermentation and was selected for further studies. Biodegradation results revealed that 59.8% of corn cob was degraded by S. carnis on the 10th day of fermentation. Enzyme production increased from the first day of fermentation till the 6th day after which it started declining. Cellulase was the first enzyme secreted into the media with an optimum production (400.34 U/mg) obtained on the 4th day while xylanase, laccase and peroxidase were produced optimally on the 6th day of degradation with specific activities of 789.6 U/mg, 489.1 U/mg and 585.4 U/mg, respectively. Maximum production of hydrolytic and oxidative enzymes was achieved at pH 6.0 which corresponds to the optimum pH for the degradation of corn cob. Increase in degradation efficiency and enzyme production was observed when the fermentation media were supplemented with metal ions [Cu2+ (75.2%), Mn2+ (77.5%)], carbon sources [xylan (81%), cellobiose (77.69%)] and nitrogen sources [glutamate (78.9%), aspartate (76.8%)], suggesting synergistic effects in the activities of the enzymes under these conditions. A striking result was obtained in the presence of sucrose as the degradation efficiency declined with about 22% compared with control. In addition, sucrose repressed the production of hydrolytic and oxidative enzymes which implies that repression in enzyme synthesis adversely affects lignocellulose degradation. The activities of the enzymes were enhanced in the presence of Mn2+, Fe2+ and Cu2+. The unique physicochemical properties exhibited by the lignocellulolytic enzymes from Sporothrix carnis suggest their suitability for exploitation in the paper and pulp, textile, dye decolorization and food industries where the cost of chemical method of lignocellulose hydrolysis is a major challenge.
