SHORTCUT OF THE PHOTOSYNTHETIC ELECTRON-TRANSFER IN A MUTANT LACKING THE REACTION CENTER-BOUND CYTOCHROME SUBUNIT BY GENE DISRUPTION IN A PURPLE BACTERIUM, RUBRIVIVAX-GELATINOSUS

A mutant lacking the reaction center-bound cytochrome subunit was cons tructed in a purple photosynthetic bacterium, Rubrivivax gelatinosus I L144, by inactivation of the cytochrome gene, Photosynthetic growth of the C244 mutant strain occurred at approximately half the rate of the wild-type strain, Although mutagenesis resulted in a greatly reduced amount of membrane-bound cytochromes c, illumination induced cyclic el ectron transfer and the generation of membrane potential in the mutant as observed in the wild-type strain, These findings are consistent wi th previous observations that the cytochrome subunit is absent in the reaction center complex in some species of purple bacteria and that th e biochemical removal of the subunit did not significantly affect the in vitro electron transfer from the soluble cytochrome c to the photos ynthetic reaction center, These results suggest that the cytochrome su bunit in purple bacteria is not essential for photosynthetic electron transfer and growth, even in those species generally containing the su bunit.