L-Glutaminase is majorly produced by microorganism including bacteria, yeast and fungi. It mainly catalyzes the hydrolysis of gamma-amido bond of L-glutamine. In the present investigation, the potent marine isolate, Bacillus subtilis JK-79 producing L-glutaminase was evaluated for the maximum L-glutaminase production by solid state fermentation (SSF). In this context, different agro-industrial residues reported in literature were tested and among them, wheat bran gave maximum L-glutaminase production (236.67 U/ml) and protein concentration (6.89 mg/ml). Statistical optimization of media components and culture conditions were successfully employed to markedly enhance the L-glutaminase production under SSF by marine B. subtilis JK-79. Optimization was sequentially performed from one factor at a time (OFAT), followed by Plackett and Burman Design (PBD) and response surface methodology (RSM). With the help of PB design, three significant factors such as moisture content, pH and L-glutamine were identified to significantly affect the L-glutaminase production. These three independent variables were then optimized by central composite design (CCD) of RSM. Maximum L-glutaminase production of 672.28 U/ml under flask condition was obtained at the predicted optimal values of moisture content of 62.5% (w/w), pH of 7.1 and glutamine of 2.44% (w/v). The maximum experimental L-glutaminase production was 680.8 U/ml, whereas the predicted value for L-glutaminase production was 672.28 U/ml, indicating a strong agreement between them. Statistical optimization has enhanced the production of the enzyme up to 2.88 fold as compared to the basal wheat bran medium. Thus, application of PBD and RSM for optimization studies proves to be an effective method for improving the L-glutaminase production and also understanding the interaction effects between the factors with minimum number of experiments.
Key words: Bacillus subtilis JK-79, L-glutaminase, Plackett-Burman design, response surface methodology, wheat bran.