PLEIOTROPIC EFFECTS OF PUF INTERPOSON MUTAGENESIS ON CAROTENOID BIOSYNTHESIS IN RUBRIVIVAX-GELATINOSUS - A NEW GENE ORGANIZATION IN PURPLE BACTERIA

Rubrivivax gelatinosus mutants affected in the carotenoid biosynthesis pathways were created by interposon mutagenesis within the puf operon . Genetic and biochemical analysis of several constructed mutants sugg est that at least crtC is localized downstream of the puf operon and t hat it is cotranscribed with this operon. Sequence analysis confirmed the genetic data and showed the presence of crtD and crtC genes downst ream of the puf operon, a localization different from that known for o ther purple bacteria. Inactivation of the crtD gene indicated that the two crt genes are cotranscribed and that they are involved not only i n the hydroxyspheroidene biosynthesis pathway as in Rhodobacter sphaer oides and R. capsulatus, but also in the spirilloxanthin biosynthesis pathway. Carotenoid genes implicated in the spirilloxanthin biosynthes is pathway were thus identified for the first time. Furthermore, analy sis of carotenoid synthesis in the mutants gave genetic evidence that crtD and crtC genes are cotranscribed with the puf operon using the ox ygen regulated puf promoter.