Abstract
A basic study to develop a turbimetric assay method for vitamin B_<12> utilizing two mutant strains of Escherichia coli is described. The mineral salts-citrate-gluocse medium of Davis and Mingioli was adapted as the basal medium. The strains employed as test organisms were E. coli #215 and #1544. The former requiring either vitamin B_<12> or methionine was derived from E. coli O-20,and the latter responding to either methionine or homocystine from E. coli ATCC 9537. Both the strains were produced in this laboratory from ultraviolet irradiated cultures of E. coli of wild types by the penicillin technique of Davis and Lederberg et al. The response of #215 to the vitamin was a little better than that of another vitamin B_<12> requiring mutant from ATCC 9637. Methionine interferes with the growth response curve of #215 only when present in amounts greater than 0.7μg per ml. The concentration of methionine, however, can be determined with #1544 as a test organism. The growth of 22 hours incubation was not affected by the presence of amino acids, B-vitamins, and nucleic acids as well as their derivatives, though the organism was stimulated in the presence of vitamin B_<12> during early stage of incubation. The assay of vitamin B_<12> in materials containing methionine and vitamin B_<12> may be possible when diluted to the measureable concentration of the vitamin and less than 0.7μg of methionine per ml of the assay medium.
