Morphologically favorable mutant of Trichoderma reesei for low viscosity cellulase production.

Metabolite production by filamentous fungi hampered because of high viscosity generated during growth. Low viscosity fermentation by mold is one of the preferred ways of large scale enzymes production. Cellulolytic enzymes play a key role during the process of lignocellulosic biomass conversion. In this study, a mutant RC-23-1 was isolated through mutagenesis (diethyl sulfate followed by UV) of Trichoderma reesei RUT-C30. RCRC-23-1 not only gave higher cellulase production but also generated lower viscosity during enzyme production. Viscosity of mutant growth was more than three times lower than parent strain. RC-23-1 shows unique, yeast-like colony morphology on solid media and small pellet-like growth in liquid media. This mutant did not spread like mold on solid media. This mutant produces cellulases constitutively when grown in sugars. Using only glucose, the cellulase production was 4.1 FPU/ml. Among polysaccharides (avicel, xylan, and pectin), avicel gave maximum of 6.2 FPU/ml and pretreated biomass (rice straw, wheat straw and sugarcane bagasse) produced 5.1-5.8 FPU/ml. At 7 L scale reactor, fed-batch process was designed for cellulase production using different carbon and nitrogen sources. Maximum yield of cellulases was 182 FPU/g of lactose consumed was observed in fed-batch process. The produced enzyme used for hydrolysis of acid pretreated rice straw (20% solid loading) and maximum of 60% glucan conversion was observed. RC-23-1 mutant is good candidate for large scale cellulase production and could be a model strain to study mold to yeast-like transformation.

Biochemical characterization of two xylanases from yeast Pseudozyma hubeiensis producing only xylooligosaccharides.

Two distinct xylanases from Pseudozyma hubeiensis NCIM 3574 were purified to homogeneity. The molecular masses of two native xylanases were 33.3 kDa (PhX33) and 20.1 kDa (PhX20). PhX33 is predominant with alpha-helix and PhX20 contained predominantly beta-sheets. Xylanase, PhX33, possesses three tryptophan and one carboxyl residues at the active site. The active site of PhX20 comprises one residue each of tryptophan, carboxyl and histidine. Carboxyl residue is mainly involved in catalysis and tryptophane residues are solely involved in substrate binding. Histidine residue present at the active site of PhX20 appeared to have a role in substrate binding. Both the xylanases produced only xylooligosaccharides (XOS) with degree of polymerization (DP) 3-7 without formation of xylose and xylobiose. These XOS could be used in functional foods or as prebiotics. Lc ms-ms ion search of tryptic digestion of these xylanases revealed that there is no significant homology of peptides with known fungal xylanase sequences which indicate that these xylanases appear to be new.