Isolation of an Escherichia coli mutant defective in cytochrome biosynthesis

A pleiotropic mutant of Escherichia coli affected in cytochrome biosynthesis was detected by anaerobic screening on a solid medium containing triphenyltetrazolium. When grown anaerobically on glycerol, nitrate and Casamino acids, this mutant exhibited a level of soluble cytochrome c552 which was ten times higher than that found in wild‐type cells. The level of membrane‐bound cytochrome b and the activity of nitrate reductase were about half the normal level. The mutant grew aerobically on succinate or d,l‐lactate at a greatly reduced rate. The mutation impairing the growth ability at the locus sox (succinate oxidation) is also responsible for the deficiency of cytochrome b, nitrate reductase and formate dehydrogenase. Mapping by transduction placed sox at 86.7 min on the chromosome, very close to the glnA locus. Genetic analysis also indicated that the elevated level of cytochrome c552 was the result of a separate mutation, the location of which is yet to be determined.