Bacterial Growth at Constant pH

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Abstract
The apparatus which provided automatic pH control has been modified to give increased accuracy in determination of the acid production during the early portion of the growth period, and to eliminate the possibility of contamination when the electrodes are inserted into the growth medium. The effects of saturation with various mixtures of N2, O2 and CO2, and also a variation of the sugar conc., have been studied, all at pH = 6. Slight decreases only in the acid production were observed when the proportions of CO2 and of O2 were greatly increased. A correlation was observed between the apparent oxidation-reduction po-tenial and the rate of acid production, a maximum in the latter corresponding, in general, with a minimum of the former. Using the plate counts, the fermenting capacity per unit of time for a single organism could be followed during the growth period. This was found to be about 26 X 10-15 equivalent of acid per hr. per organism during the "logarithmic" period and to decrease to 13% of this value after 50 hrs. The generation time tended to increase as the products of fermentation accumulate, although the pH is kept constant [see B. A. 10(3): Entry 6409].

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