Metabolism of cobalamins by a soil microorganism.

The occurrence in soil of a large group of bacteria which require vitamin B12 has been reported by Lochhead and Thexton (1952). Thirty cultures obtained from 534 isolates showed dependence upon vitamin B12 for growth. Lochhead and Burton (1954) grouped these 30 cultures into 10 types, based on morphological and physiological characteristics. A study of the nature of the vitamin B12 requirements of 19 of these cultures, representing all of the 10 types, has been made by Ford and Hutner (1957). Goldberg et al. (1957) reported on the nutrition of one of these organisms, culture no. 38, a member of the type III group provisionally classified by Lochhead and Burton (1954) as belonging to the genus Arthobacter, and indicated that the organism is specific in its growth requirement for 5, 6-dimethylbenzimidazole-cyano-cobalamin.2 However, in the course of investigations of the biological properties of several B12 vitamins it was observed (Seaman and Sanders, 1957) that the cobalamin requirement of this organism, commonly termed "Lochhead 38" could be replaced by factor B, the compound formed from 5, 6-dimethylbenzimidazole-eyanocobalamin by removal of the nucleotide portion of the molecule. This unanticipated finding prompted a reexamination of the vitamin B12 requirement of Lochhead 38 and an investigation