Process optimization for obtaining a maximum yield of alkaline thermostable lipase from Bacillus stratosphericus-MK788130

Since last few decades, continuous efforts are being made to screen the lipase producing bacterial strains from the environment because of its diverse commercial applications. In this study, Bacillus stratosphericus MK-788130 was isolated from a frying oil contaminated soil although it was previously thought to be the atmospheric bacterium. It showed lipolytic zones of 0.44 mm, 0.51 mm and 0.37 mm on peptone yeast agar, olive oil hydrolysis agar and chromogenic plate agar respectively. It produced an extracellular lipase 42.7 µM/ml. This bacterium preferred acidic pH 5 for growing optimally at 45 °C when the medium was supplemented with 1% olive oil. The olive oil induced its growth up to 9 hours. The protein content of the purified lipase was 85 mg/ml as compared to its crude form i.e. 220 mg/ml. The purified lipase was found to be alkaline thermostable as its optimum activity was observed at pH 9 and 90 °C. The factors that optimized its activity included 0.1mM Na ions (0.06 U/ml), 0.1 mM fructose (0.1 U/ml), 1% olive oil (0.7 U/ml), 1% corncob (0.1 U/ml), 1% yeast extract (0.05 U/ml), 1% casein (0.05 U/ml) and 0.1 mM commercially available detergents (0.06-0.07 U/ml). It was observed stable with metal ions (Na, Fe and Ca), induced by Tween 80, Tween 20 but inhibited by Triton X-100 and SDS. The purified lipase showed a polypeptide of 14 kDa on SDS-PAGE. Its property as a biosurfactant as well as in oil bioremediation has broadened its application in the biotechnological industry.