The Rhodobacter sphaeroides PufX protein is not required for photosynthetic competence in the absence of a light harvesting system.

The effects of deletion of the gene encoding the PufX protein from Rhodobacter sphaeroides have been examined using bacterial strains with simplified photosystems. We find that the PufX protein is required for photosynthetic growth in strains which have the LH1 antenna complex, but is not required in a reaction centre-only strain, suggesting that the PufX protein does not directly facilitate cyclic electron transfer between the reaction centre and the cytochrome bc1 complex. The influence of PufX and carotenoid type on the size of the reaction center/LH1 core complex has also been examined in these strains.