Bacterial Growth with Automatic pH Control

Abstract

An apparatus is described by means of which the pH of a nutrient medium can be accurately and automatically controlled during growth. The apparatus depends upon the measurement of the pH with a glass electrode, and the control of the addition of a solution of alkali by means of a photo-electric relay actuated by the deflection of a beam of light by the mirror of an electrometer. The apparatus functions for indefinite periods with a minimum of attention. It was used in the study of the acid production during the growth of L. acidophilus at different controlled pH values and, for comparison, with no pH control. Acid production was greatly increased by maintaining the pH at relatively low values. It has, however, been found necessary to study the effect of the dissolved gases on the bacterial growth. The studies confirmed the conclusion of others that, at least for the organism under observation, CO2 is necessary for such growth.