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

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.

Effect of partial pressure of CO2 on the production of thermostable alpha-amylase and neutral protease by Bacillus caldolyticus.

Controlling the concentration of dissolved oxygen is a standard feature in aerobic fermentation processes but the measurement of dissolved CO2 concentrations is often neglected in spite of its influence on the cellular metabolism. In this work room air and room air supplemented with 5% and 10% carbon dioxide were used for aeration during the cultivation of the thermophilic microorganism Bacillus caldolyticus (DSM 405) on starch to produce alpha-amylase (E.C. 3.2.1.1) and neutral protease (E.C. 3.4.24.27/28). The increased CO2 concentrations resulted in a 22% raise in activity of secreted alpha-amylase and a 43% raise in protease activity when compared with aeration with un-supplemented room air. There was no effect on the final biomass concentration. Furthermore, the lag-phase of fermentation was reduced by 30%, further increasing the productivity of alpha-amylase production. Determinations of dissolved CO2 in the culture broth were conducted both in situ with a probe as well as using exhaust gas analysis and both the methods of quantification showed good qualitative congruence.

Relevance of microbial coculture fermentations in biotechnology.

The purpose of this article is to review coculture fermentations in industrial biotechnology. Examples for the advantageous utilization of cocultures instead of single cultivations include the production of bulk chemicals, enzymes, food additives, antimicrobial substances and microbial fuel cells. Coculture fermentations may result in increased yield, improved control of product qualities and the possibility of utilizing cheaper substrates. Cocultivation of different micro-organisms may also help to identify and develop new biotechnological substances. The relevance of coculture fermentations and the potential of improving existing processes as well as the production of new chemical compounds in industrial biotechnology are pointed out here by means of more than 35 examples.