Journal of Applied Microbiology, Vol.125, No.4, 1076-1093, 2018
Statistical enhancement of lipase extracellular production by Bacillus stratosphericus PSP8 in a batch submerged fermentation process
AimThe aim of this study was to isolate and identify lipolytic bacteria. Perform a statistical stepwise physicochemical optimization for maximum production of extracellular lipase and its validation in a bioreactor. Methods and ResultsSeveral lipolytic bacteria were isolated from petroleum hydrocarbon-polluted soil. The strain expressing the highest lipase activity (47Uml(-1)) was genetically identified as Gram-positive Bacillus stratosphericus PSP8 (NCBI GenBank accession no. ). The response surface methodology (RSM)-central composite face centre (CCF) design of experiments was performed based on the preselected levels of the studied parameters obtained from the performed one-factor-at-a-time sequential experiments. A second-order polynomial model was predicted and improved the lipase production by approximately 1
6-fold. Preliminary scaling up of the validated optimized process was carried out in a batch 10-l stirred tank bioreactor, applying the optimum predicted operating conditions; pH 6 98, 34 8 degrees C, 2 2x10(6) cells per ml, 200revmin(-1), 4 82gl(-1) tributyrine concentration, 1% sucrose and 0 1% yeast extract. This yielded 89Uml(-1) at the late log phase of bacterial growth (48h). Logistic kinetic model effectively characterized the submerged fermentation process, and the maximum specific growth and lipase production rates were estimated to be 0 338 and 0 164h(-1) respectively. ConclusionsThe mesophilic and neutrophilic B. stratosphericus PSP8 isolated from petroleum hydrocarbon-contaminated soil is a proper source of lipase. The closeness of the predicted response with that of the experimental value and the enhancement of lipase productivity in fermenter scale by approximately 1 9-fold, showed that statistically optimized design can be used in order to improve the lipase production to meet the increasing demand. Significance and Impact of the StudyThe RSM-CCF statistical optimization is useful for optimizing a large number of variables and studying their interactive effects on extracellular lipase production.