Bacterial Fermentation for Protease Production in Fermenters: Impact of Oxygen Transfer Characteristics and Rheological Features on Scale up Process

Abstract

Abstract Development of microbial fermentation and scale up processes for the production of value added metabolites including enzymes derives importance in industrial research. Though there are numerous studies on the production of industrial enzymes especially proteases using shake flasks, scale up studies with respect to mass transfer and hydrodynamics of fermentation in bioreactors are limited. The study deals with the production and scale up of an extracellular alkaline protease using Bacillus sp. S2 MTCC 13117 from shake flask level to 300 L fermenter. Glucose, DO, and pH profiles during scale up were studied in detail. Scale up parameters related to oxygen dynamics such as oxygen uptake rate (OUR), oxygen transfer rate (OTR), specific OUR and volumetric oxygen transfer coefficient (kLa) were evaluated. Results showed that yield coefficients with respect to biomass, product and substrate were reproduced at different levels of protease scale up in the batch mode of fermentation. Protease production was subjected to catabolite repression and it was shown to be derepressed at low specific growth rates. It was observed that the bioprocess of protease production was an aerobic one and was highly influenced by hydrodynamic conditions in the bioreactors. Use of bioreactor systems enabled effective oxygen transfer and the duration for achieving optimal protease production was reached earlier (t = 36 h in 19 L and t = 24 h in 300 L) when compared to shake flask experiments (t = 44 h). Besides, improvement in the productivity of the fermentation was substantiated by several other scale up parameters such as aeration rate, impeller tip speed, gas hold up and superficial gas velocity for effective mixing and rheological properties of the broth during fermentation in 19 and 300 L fermenters.