Enzymatic saccharification of pretreated rice straw by cellulase produced from Bacillus carboniphilus CAS 3 utilizing lignocellulosic wastes through statistical optimization

A marine bacterium, Bacillus carboniphilus CAS 3 was subjected to optimization for cellulase production utilizing cellulosic waste through response surface methodology. Plackett – Burman and Central composite design was employed and the optimal medium constituents for maximum cellulase production (4040.45 U/mL) were determined as rice bran, yeast extract, MgSO4·7H2O and KH2PO4 at 6.27, 2.52, 0.57 and 0.39 g/L, respectively. The cellulase produced was purified to the specific activity of 434.94 U/mg and 11.46% of recovery with the molecular weight of 56 kDa. The optimum temperature, pH and NaCl for enzyme activity was determined as 50 °C, 9 and 30% and more than 70% of its original activity was retained even at 80 °C, 12 and 35% respectively. Further, enzymatic saccharification of pretreated rice straw yielded about 15.56 g/L of reducing sugar at 96 h, suggesting that the purified cellulase could be useful for production of reducing sugars from cellulosic biomass into ethanol.