Genetic and phenotypic analyses of the rdx locus of Rhodobacter sphaeroides 2.4.1.

Previously, we reported that rdxB, encoding a likely membrane-bound two [4Fe-4S]-containing center, is involved in the aerobic regulation of photosystem gene expression in Rhodobacter sphaeroides 2.4.1. To further investigate the role of rdxB as well as other genes of the rdxBHIS operon on photosystem gene expression, we constructed a series of nonpolar, in-frame deletion mutations in each of the rdx genes. Using both puc and puf operon lacZ fusions to monitor photosystem gene expression, under aerobic conditions, in each of the mutant strains revealed significant increased photosynthesis gene expression. In the case of mutations in either rdxH, rdxI, or rdxS, the aerobic induction of photosystem gene expression is believed to be indirect by virtue of a posttranscriptional effect on cbb(3) cytochrome oxidase structure and integrity. For RdxB, we suggest that this redox protein has a more direct effect on photosystem gene expression by virtue of its interaction with the cbb(3) oxidase. An associated phenotype, involving the enhanced conversion of the carotenoid spheroidene to spheroidenone, is also observed in the RdxB, -H, -I, and -S mutant strains. This phenotype is also suggested to be the result of the role of the rdxBHIS locus in cbb(3) oxidase activity and/or structure. RdxI is suggested to be a new class of metal transporter of the CPx-type ATPases.