Conditional mutations of Salmonella typhimurium that are suppressed by anaerobic or aerobic environments

Mutant strains of Salmonella typhimurium were isolated that grew on a minimal medium only in an aerobic environment or only in an anaerobic environment. Mutants that grew only anaerobically were induced by mutagens such as deoxybromouridine and deoxyiodouridine that promote AT → GC transitions whereas those that grew only aerobically were induced by mutagens such as N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG) that promote GC → AT transitions. This mutagen selectivity and the ability of mutant strains to grow on minimal medium in one environment suggested that the changes in DNA occurred outside the coding regions of genes. These results provide a means to investigate the mechanisms by which organisms adapt to, or are restricted by, their environment.