The Isolation and Characterization of Three Types of Vitamin B6 Auxotrophs of Escherichia coli K12

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Abstract
Approximately 500 vitamin B6 auxotrophs were isolated from 18 independent cultures of E. coli strain CR63. None grew in minimal medium supplemented with 2''-hydroxypyridoxine. Eighteen auxotrophs which arose independently were further characterized. All of them were defective in vitamin B6 synthesis rather than in an aminotransferase involved in vitamin B6 utilization. Two different phenotypes were recognized: oxidase mutants which grew only when supplied with pyridoxal or pyridoxal 5''-phosphate and Pre Pn mutants which would also grow with pyridoxine or pyridoxine phosphate. Oxidase mutants were confined to a single linkage group, but data from interrupted mating experiments established that Pre Pn mutants fall into 2 linkage groups which are possibly identical to pdxA and pdxB. All mutations in the pdxA region were allelic rather than located in 2 closely linked genes.