ANALYSIS OF THE CBBXYZ OPERON IN RHODOBACTER-SPHAEROIDES

Three genes, cbbX, cbbY, and cbbZ were found downstream from the form I ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) genes of R hodobacter sphaeroides. As in chemoautotrophic bacteria, cbbZ was show n to encode phosphoglycolate phosphatase (PGP), whereas the identities of cbbX and cbbY are not known. To determine the physiological functi on of the cbbXYZ gene products, we constructed R. sphaeroides strains in which the genes were inactivated and characterized the resultant mu tant strains according to growth phenotype and levels of RubisCO and P GP. Only a mutation in cbbX resulted in a discernible phenotype, namel y, impaired photoautotrophic growth. No PGP activity was observed in a ny of the mutants, suggesting that the three genes are transcriptional ly linked. Studies with a spontaneous chemoautotrophic competent deriv ative of the CBBX mutant suggested that the cbbXYZ gene products are n ot essential for chemoautotrophic growth. PGP activity determined in t he wild-type strain grown under a variety of growth conditions, and in various strains containing mutations in Calvin-Benson-Bassham cycle s tructural and regulatory genes, indicated that transcription of the cb b(I) operon influenced expression of the downstream cbbXYZ operon.