Effect of aerobic growth conditions on the soluble cytochrome content of the purple phototrophic bacterium Rhodobacter sphaeroides: Induction of cytochrome c554

When grown anaerobically in the light, Rhodobacter sphaeroides contains appreciable quantities of cytochromes c 2 and c′, but smaller amounts of other soluble cytochromes such as cytochrome c 551.5, cytochrome c 554, and an oxygen-binding heme protein. When R. sphaeroides is mass cultured aerobically in the dark to stationary phase, the content of cytochrome c 2 does not change appreciably, whereas cytochrome c 554 is approximately 8-fold more abundant, cytochrome c′ is at least 10-fold less abundant, and cytochrome c 551.5 is fivefold lower than in the phototrophically grown cells. These observations confirm previous literature reports that in this organism a cytochrome c 553 (or c 554 in our experience) is more abundant when cells are grown aerobically. Furthermore, the aerobic cytochrome c 554 is positively identified with the previously characterized minor cytochrome c 554 component of anaerobic photosynthetic cells. Preliminary sequence results show that cytochrome c 554 is a member of the cytochrome c′ structural family, but differs from normal cytochromes c′ in having a methionine sixth ligand to the heme. The levels of electron carrier proteins of low redox potential had previously been reported to be less in aerobic than in photoheterotrophic cells and we have verified that observation for the specific examples of cytochromes c′ and c 551.5. The oxygen binding heme protein, SHP, is not induced by aerobic growth.