Positive effect of reduced aeration rate on secretion of alpha-amylase and neutral proteases during pressurised fermentation of thermophilic Bacillus caldolyticus

• CO2 positively affects formation of secreted enzymes by Bacillus caldolyticus.
• CO2 concentration in medium increased by reducing aeration rate.
• Oxygen transfer rate increased by raising overhead pressure.
• Results indicate importance of CO2 during scale up of fermentation process.

The thermophilic microorganism Bacillus caldolyticus was incubated in laboratory scale stirred bioreactors under pressurised conditions at different aeration rates. Increased amounts of CO2/bicarbonate were solubilised under the chosen conditions. A reduction in aeration rate from 1 vvm to 0.1 vvm resulted in accumulation of CO2 and bicarbonate up to 126 mg l−1 and 733 mg l−1, respectively and also increased secretion of α-amylase and neutral proteases (increases of 123% and 52%, respectively). In this paper, the effect of reduced aeration rate on CO2/bicarbonate concentration and enzyme activities is presented. The selected fermentation conditions are closely related to those prevalent in large scale bioreactors and may offer the possibility of achieving high enzyme yields at reduced aeration costs on an industrial scale.