Cellulose-degrading enzymes from Aspergillus terreus D34 and enzymatic saccharification of mild-alkali and dilute-acid pretreated lignocellulosic biomass residues

Background: Production of cellulose-degrading enzymes from Aspergillus terreus D34 using different growth substrates was studied under solid-state cultivation. We have tested two lignocellulosic biomass residues viz., rice straw (RS) and sugarcane bagasse (BG), both separately and in combinations, and crystalline cellulose as a sole source of carbon for cellulase production. We also demonstrated different cellulase cocktail formulations and enzymatic saccharification studies on mild-alkali and dilute-acid pretreated RSand BG-biomass residues. Results: Substrate-specific non-denaturing native gels showed two exoglucanases, four endoglucanases, three β-glucosidases, and four xylanases in the microbial culture extract of RS-grown cells. While in the BG-culture extract, two exoglucanases, five endoglucanases, three β-glucosidases, and four xylanases were detected. Similarly, in crystalline cellulose-grown culture extract, three exoglucanases, four endoglucanases, one β-glucosidase, and two xylanases were detected. However, the cellulase compositions were highly varied with the culture extracts obtained from the mixed biomass (RSBG) growth substrate. We found that few enzymes were specifically induced while others were repressed in RSBG-grown cultures. Enzymatic saccharification resulted in the production of maximum reducing sugars of 0.733 and 0.498 g g with mild-alkali treated RSand BG-biomass residues with saccharification yields reaching up to 82.8% ± 1.0% and 59.3% ± 1.7%, respectively. Conclusions: The cellulase activities, namely FPase, CMCase, avicelase, β-glucosidase, and endoxylanase, were significantly higher in the BG-grown culture extract. Optimization of microbial growth carbon sources produced an efficient cellulase enzyme cocktail mixture with an approximately twofold higher total cellulase (FPase) activity that drastically reduced the required amount of enzyme (in terms of unit volumes) for enzymatic hydrolysis studies.