Substitution of Thymine for “Folic Acid” in the Nutrition of Lactic Acid Bacteria

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Abstract
Thymine and its nucleoside, thymidine, substituted for folic acid in the growth of Streptococcus lactis R and related lactic acid streptococci. At least 5000 times more thymine was required than folic acid. Thymine had a high degree of biol. specificity; a large number of pyri-midinc, purines, nucleic acids and similar compounds were inactive. Adenine was necessary for max. growth of S. lactis with either thymine or folic acid; guanine or xanthine could substitute for adenine but were less effective. Folic acid could not be detected in streptococcus cells grown in thymine medium. Similar results were obtained with 3 spp. of folic acid-requiring lactobacilli. However, replacement of folic acid by thymine here was only partially effective since considerably less than max, fermentation occurred even with excess thymine. The theory is advanced that folic acid participates directly or indirectly as a coenzyme in the synthesis of thymine or a related compound in the lactic acid streptococci.

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