Application of pH and pO2 Probes During Bacillus caldolyticus Fermentation: An Additional Approach for Improving a Feeding Strategy

J. Bader, K. Schwab, R. Bajpai and B. Neumann

Abstract
In this paper, three different feeding strategies are presented and compared for fed-batch operation of bioreactor for production of α-amylase by Bacillus caldolyticus: constant volumetric specific feed rate, variable feed rate based on responses of pO2 probe when subjected to short pulses in feed rate, and exponentially increasing feeding rate supported by pH and pO2 probes. The best strategy was found to be the exponential feeding supported by pH and pO2 probes giving a specific activity of 15.7 Uα-amylase .g–1 dry weight as well as a productivity of 2.3 Uα-amylase .g–1 dry weight .h–1 and negligible acetate formation. Each of the probes offers information concerning different regions of metabolic state. Using the responses of these two probes, a feed medium with balanced ratio of starch and casitone was obtained. This medium composition resulted in increased titre as well as productivity of enzyme even with the simple exponential feeding strategy.

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Keywords
Bacillus caldolyticus, pO2 and pH feed-back strategy, exponential feeding, fed-batch, α-amylase