Bacterial Growth at Constant pH

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Abstract
A method for the production of oxygen-free mixtures of CO2 and N was developed. With the aid of these mixtures and an apparatus for automatic pH control [see B. A. 10(3) entry 6409], the growth, acid production, and apparent redox potentials of cultures of L. acido-philus have been studied at pH 6 under anaerobic con-ditions. The observation that CO2 is essential for the growth of this organism has been confirmed. Gold electrodes appear to respond more readily than Pt electrodes to changes in the oxidation-reduction balance of the system. During anaerobic growth the Eh (gold) drops rapidly to a minimum of about [long dash]190 mv., then increases to a value of about [long dash]150 mv. after which it slowly returns to the minimum value, which appears to be a characteristic of the bacteria, having been obtained in all anaerobic cultures. Using a more suitable medium than in previous expts., the measurements of growth and acid production, at a constant pH of 6, have been compared with similar measurements in normal cultures. Control of the pH resulted in a 4-fold increase of the bacterial population and a 9-fold increase of the acid production.

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