EFFECT OF REPEATED ADDITIONS OF SUBOPTIMUM AMOUNTS OF A REQUIRED VITAMIN ON GROWTH AND ACID PRODUCTION OF LACTOBACILLI

¹ Zoller Dental Clinic and Department of Microbiology, University of Chicago, Chicago, Ill.

Growth response and acid production by lactobacilli to multiple suboptimum amounts of a required vitamin, supplied over a period of 12 days or more, were compared with the response when the same total amount of vitamin was supplied at the time of inoculation in the conventional way. A basal medium of acid hydrolyzed casein, glucose, acetate, salts, and supplements was used.

The periodic additions of small amounts of a required vitamin did not support as full growth as the same total amount of vitamin given at the start. However, the periodic additions evidently caused some metabolic stimulus, and more viable cells usually were found toward the end of the experimental period under such conditions.

In lactobacillus cultures supplied the periodic small amounts of vitamin, pH values usually were not as low as, although at times they approached, the pH values reached when all the vitamin was supplied at the start. When the acid resulting from cell metabolism supported by repeated small amounts of vitamin was neutralized periodically, lactobacilli were able to again lower the pH over the first few periods as more vitamin was supplied, but in later periods little change in pH resulted when additional small amounts of vitamin were supplied.