Optimization of growth medium for protease production by Haloferax Lucentensis VKMM 007 by response surface methodology

ABSTRACT

The production of halophilic thermostable protease by Haloferax lucentensis VKMM 007 was optimized using a statistical approach. In accordance with factorial design, soluble starch, gelatin, KCl and MgSO4 were selected among 27 variables tested. Next, a second-order quadratic model was estimated and optimal medium concentrations were determined based on quadratic regression equation generated by model. These were 5.14 g L-1 of KCl, 6.57 g L-1of MgSO4, 9.05 g L-1of gelatin and 5.27 g L-1of soluble starch in high salts media supplemented with 0.5 percent (w/v) of beef extract and peptone, respectively. In these optimal conditions, the obtained protease concentration of 6.80 U mL-1 was in agreement with the predicted protease concentration and was further improved to 7.02 U mL-1 by increasing the concentration of NaCl in the medium to 25 percent (w/v). An overall 4.0-fold increase in protease production was achieved in the optimized medium compared to activity obtained in initial medium.