A mutant of Bacillus subtilis has been isolated that fails to grow on succinate as the source of carbon, yet grows on glucose. Intact cells of the mutant and cytoplasmic membranes derived therefrom lack cytochromes a and a3 but contain a cytochrome o-like pigment, which forms a photodissociable compound with CO and is reactive with oxygen. The mutation in the genome has been located and lies at about 130 degrees on the chromosomal map between the metC and pyrD loci. The designation cox is suggested for this gene.