Bioprocess Optimization for Enhanced Production of Bacterial Cellulase and Hydrolysis of Sugarcane Bagasse

Abstract

Cellulolytic enzymes have gained considerable importance as potential candidates for the efficient bioconversion of agricultural biomass into second-generation biofuel. This study aimed to improve cellulase production from a bacterial strain isolated from cow dung. The biochemical and molecular identification was performed, and the capacity of the isolated bacterium to hydrolyze sugarcane bagasse was also determined. Response surface methodology (RSM) and one-variable-at-a-time (OVAT) designs were employed to maximize the cellulase production. The bacterium identified as Bacillus subtilis gave the highest cellulase yield at temperature of 45 °C, pH-7.0, and 72 h of incubation time. Optimization by the Plackett–Burman design consisting of 12 experimental runs at two levels of nine independent variables displayed the significant contribution of galactose (22%) and sodium nitrate (16%) in cellulase production. The responses in the form of contour and 3D plots (generated by Box-Behnken design) predicted maximum cellulase production with an activity of 0.8 U/mL/min in a medium containing 3.0 g/L carboxymethyl cellulose, 3.0 g/L galactose, 0.5 g/L sodium nitrate, 0.75 g/L KH₂PO₄, and 0.375 g/L MgSO₄·7H₂O. The experimentally deduced activity value was 0.698 U/mL/min, showing 90% validity of the predicted value and gave a threefold increase in cellulase production. The process adequately represented by the quadratic model (p < 0.0343) for all the responses was significant. Results obtained show that optimization of fermentation medium favored the increased production of cellulase by the bacterium. The bacterial isolate B. subtilis CD001 was found to be a potential candidate to hydrolyze the lignocellulosic feedstock, sugarcane bagasse.