CELL RECYCLING STUDIES FOR ALPHA-AMYLASE PRODUCTION BY BACILLUS-AMYLOLIQUEFACIENS

Production of alpha-amylase by a strain of Bacillus amyloliquefaciens was investigated in a cell recycle bioreactor incorporating a membrane filtration module for cell separation. Experimental fermentation stud ies with the B. amyloliquefaciens strain WA-4 clearly showed that inco rporating cell recycling increased alpha-amylase yield and volumetric productivity as compared to conventional continuous fermentation. The effect of operating conditions on alpha-amylase production was difficu lt to demonstrate experimentally due to the problems of keeping the pe rmeate and bleed rates constant over an extended period of time. Compu ter simulations were therefore undertaken to support the experimental data, as well as to elucidate the dynamics of alpha-amylase production in the cell recycle bioreactor as compared to conventional chemostat and batch fermentations. Taken together, the simulations and experimen ts clearly showed that low bleed rate (high recycling ratio) various a high level of alpha-amylase activity. The simulated fermentations rev ealed that this was especially pronounced at high recycling ratios. Vo lumetric productivity was maximum at a dilution rate of around 0.4 h(- 1) and a high recycling ratio. The latter had to exceed 0.75 before vo lumetric productivity was significantly greater than with conventional chemostat fermentation.