Qualitative assays and quantitative determinations of xylanolytic enzymes of wood rot fungi from Dagaga and Gambo forests, Ethiopia

Abstract

Xylan is a second widely available polysaccharide in nature and can be enzymatically degraded for the production of sugars. The complete biodegradation of xylan needs synergistic action of different xylanolytic enzymes. In this research, potential xylanolytic activities of the wood rot basidiomycete fungi from Dagaga and Gambo forests were screened. Xylanases of the potential fungi were also quantitatively determined. Clear zones round the cultures on xylan supplemented agar media of isolate 011-1D (Trametes gibbosa) and 030-1D (Phellinus tremulae) were significantly wider than other isolates. The fungal isolates differently responded to the incubation days both in submerged and solid-state fermentations and most isolates gave higher xylanase yield in solid-state fermentation than in submerged fermentation. The enzymes were active and stable in the temperature range of 40 to 55oC and pH range of 4.0 to 6.0. Incubation temperature of 30 to 35oC and pH of 5.0 to 7.0 were found to be suitable for production of the xylanases from the fungal isolates. Among the supplemented carbon sources, carboxymethylcellulose, xylan and sucrose were found suitable for xylanase productions but most isolates differently responded to the nitrogen source supplementations. MgSO4, ZnSO4 and CaCl2 were also found to be suitable divalent metallic ions for the productions of the enzymes. The isolates could be used for hydrolysis lignocellulosic xylan to 5-carbon sugars by optimizing their growth conditions.