Specific Action of 4-Nitropyridine 1-Oxide on Escherichia coli K-12 Pro+ Strains Leading to the Isolation of Proline-Requiring Mutants: Isolation and Characterization of Pro− Mutants

A specific action of 4-nitropyridine 1-oxide on Escherichia coli K-12 Pro + strains leading to highly efficient, selective isolation of Pro − mutants is described. Incubation of Pro + cells with a sublethal concentration of 4-nitropyridine 1-oxide in Penassay broth gave Pro − mutants, which lacked either the biosynthetic pathway of proline from glutamic acid to glutamyl γ-phosphate ( proB − ) or the pathway from glutamyl γ-phosphate to glutamic γ-semialdehyde ( proA − ) or both. Pro − mutants, which have the metabolic block between Δ 1 pyrroline-5-carboxylate (the cyclized dehydration product of glutamic γ-semialdehyde) and proline ( proC − ) were not found among survivors. Treatment of Pro + cells with N -methyl- N ′-nitro- N -nitrosoguanidine led to isolation of all three types of Pro − mutants, suggesting that the action of 4-nitropyridine 1-oxide on Pro + cells is apparently distinct from the action of N -methyl- N ′-nitro- N -nitrosoguanidine. F-duction and interrupted mating experiments led to determination of the correlation between proline loci and the biosynthetic pathway of proline from glutamic acid.