SUMMARY: The growth requirements of a vitamin B-dependent soil bacterium (strain 544), provisionally classified as belonging to the genus , were studied. The organism showed a high specificity for vitamin B12; of the naturally occurring analogues tested, only α-(5-hydroxybenzimidazolyl)-cobamide cyanide and α-(2-methylmercaptoadenyl)cobamide cyanide possessed some growth-promoting activity (less than 10%). The anilide and the ethylamide of the monocarboxylic acid of vitamin B inhibited growth and the inhibition was reversed by the vitamin. A medium and a procedure for vitamin B assay using strain 544, is described. Comparative assays with and 7M are given and their differential usefulness for differentiating the various congeners of vitamin B discussed.

Addition of vitamin B to B-deficient cell suspensions of strain 544 stimulated the biosynthesis of methionine and the oxidation of propionate, valerate, isoleucine and valine. The endogenous respiration and oxidation of glucose, butyrate, leucine and lysine were only slightly enhanced by vitamin B.


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