Genetic and biochemical analyses of pantothenate biosynthesis in Escherichia coli and Salmonella typhimurium

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Abstract
Pantothenate (pan) auxotrophs of E. coli K-12 and S. typhimurium LT2 were characterized by enzymatic and genetic analyses. The panB mutants of both organisms and the pan-6 (panA) mutant of S. typhimurium are deficient in ketopantoate hydroxymethyltransferase, whereas the panC mutants lack pantothenate synthetase. panD mutants of E. coli K-12 are deficient in aspartate 1-decarboxylase. All mutants showed only a single enzyme defect. The finding that the pan-6 mutant was deficient in ketopantoate hydroxymethyltransferase indicates that the genetic lesion is a panB allele. The pan-6 mutant therefore is deficient in the utilization of .alpha.-ketoisovalerate rather than the synthesis of .alpha.-ketoisovalerate, as originally proposed. The order of the pan genes of E. coli K-12 was determined by phage P1-mediated 3-factor crosses. The clockwise order was aceF panB panD panC tonA on the genetic map of E. coli K-12. The 3-factor crosses were greatly facilitated by use of a closely linked transposon Tn10 as the outside marker. Supplementation of E. coli K-12 auxotrophs with a high concentration of pantothenate or .beta.-alanine increased the intracellular CoA level 2- to 3-fold above the normal level. Supplementation with pantoate or ketopantoate resulted in smaller increases.