Effect of Aeration and Agitation Rates on Alkaline Protease Production by Bacillus licheniformis UV-9 Mutant

Purpose: The aim of the present study was to investigate the most suitable value of volumetric mass transfer coefficient for the maximum yield of alkaline protease by B. licheniformis UV-9. Material and Methods: The effects of various aeration (0.5 to 2.5 vvm) and agitation rates (300-700 rpm) on cell growth, glucose consumption and protease production by B. licheniformis UV-9 were studied in a 2 L stirred tank bioreactor. Volumetric mass transfer coefficient values were measured by dynamics gassing-out techniques at each aeration and agitation rate. Results and Conclusion: Maximum cell biomass (3.41 g/L) and protease yield (1270.20 PU/mL) were obtained at aeration rate of 2 vvm and agitation speed of 500 rpm. Volumetric mass transfer coefficient and oxygen transfer rate were found to be highly dependent on aeration and agitation rates. Their values in the fermented broth increased with the increase of aeration and/or agitation rates. However, the values of kinetic parameters were found maximum at 72 h-1 of volumetric mass transfer coefficient and 3.90 mol m-3 h-1 of oxygen transfer rate, corresponding to 2 vvm and 500 rpm. This correlation of volumetric mass transfer coefficient and yield coefficients would be used as an instructive tool in scale up process of protease production.