Statistical optimization of cultural medium composition of thermoalkalophilic lipase produced by a chemically induced mutant strain of Bacillus atrophaeus FSHM2.

Extremophilic microbial derived lipases have been widely applied in different biotechnological processes due to their resistance to harsh conditions such as high salt concentration, elevated temperature, and extreme acidic or alkaline pH. The present study was designed to overproduce the halophilic, thermoalkalophilic lipase of Bacillus atrophaeus FSHM2 through chemically induced random mutagenesis and optimization of cultural medium components assisted by statistical experimental design. At first, improvement of lipase production ability of B. atrophaeus FSHM2 was performed through exposure of the wild bacterial strain to ethidium bromide for 5-90 min to obtain a suitable mutant of lipase producer (designated as EB-5, 4301.1 U/l). Afterwards, Plackett-Burman experimental design augmented to D-optimal design was employed to optimize medium components (olive oil, maltose, glucose, sucrose, tryptone, urea, (NH4)2SO4, NaCl, CaCl2, and ZnSO4) for lipase production by the EB-5 mutant. A maximum lipase production of 14,824.3 U/l was predicted in the optimum medium containing 5% of olive oil, 0.5% of glucose, 0.5% of sucrose, 2% of maltose, 2.5 g/l of yeast extract, 1.75 g/l of urea, 1.75 g/l of (NH4)2SO4, 2.5 g/l of tryptone, 2 g/l of NaCl, 1 g/l of CaCl2, and 1 g/l of ZnSO4. A mean value of 14,773 ± 576.9 U/l of lipase was acquired from real experiments.