Microbiological assay of vitamin B12 with a mutant strain of Escherichia coli.

Two strains of Lactobacillus leichmanii, ATCC 7830 and ATCC 4797, are generally used for vitamin B12 assay. However, the complex growth requirements and the lack of specificity to vitamin B12 of these lactic acid bacteria make the determination of vitamin B12 difficult (Hoffmann et al., 1948; Skeggs et al., 1948; Snell et al., 1948; Capps et al., 1949; Kitay et al., 1949; Peeler et al., 1949; Winsten and Eigen, 1949; Thompson et al., 1950; Emery et al., 1951). Euglena responds to the vitamin more specifically and to a much lower concentration, but the prolonged time of incubation (4 to 7 days) is a handicap in routine assay (Hutner et al., 1949). Davis and Mingioli (1950) reported the isolation of a number of mutants of Escherichia coli which require either vitamin B12 or methionine for growth in mineral medium. In contrast to the lactic acid bacteria, the B12requiring mutants did not respond to thymidine. Because of the simple medium required, ease of growing the organism, and the specificity of its B12 requirement, a study was made to ascertain the suitability of such a mutant as assay organism for vitamin B12. Bessell et al. (1950) used mutant E. coli 113-3 and Harrison, Lees, and Wood (1951) used a mutant of E. coli for a plate assay of B12. Johansson (1951) reported briefly a turbidimetric procedure. At the time of completion of this work, Burkholder (1951) reported the study of the same mutant for B12 assay in a modified medium.