The Effects of Pyrimidines on the Growth of Lactobacillus casei

Abstract

The response of L. casei to individual pyrimidines was studied in a Landy and Dicken-type medium. 0.005 to 1 mg. of subst. was added to 10 ml. of (1) the basal medium, (2) medium plus enough thymine to produce full response, and (3) medium plus enough folic acid to give half-maximal growth. In thymine derivatives where oxygens were replaced by an imino or thio group, the action of thymine was simulated. Imino substitution weakened the activity. Imino compds. acted as such and not primarily by deaminization to thymine. Thio compds. varied in their activity. Substitution into the 6-position of thymine usually abolished activity. Replacement of the methyl group of thymine by an amino or hydroxy group resulted in inhibition. Bromouracil was inhibitory with thymine as the nutrient but had little or no effect with folic acid as the nutrient. Nitrouracil was inhibitory with folic acid at concs. which had little or no effect on the growth with thymine.