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A Redox-Responsive Pathway for Aerobic Regulation of Photosynthesis Gene Expression in Rhodobacter sphaeroides 2.4.1

1998; American Society for Microbiology; Volume: 180; Issue: 16 Linguagem: Inglês

10.1128/jb.180.16.4044-4050.1998

1098-5530

James P. O’Gara, Jesus M. Eraso, Samuel Kaplan,

Microbial Fuel Cells and Bioremediation

ABSTRACT To further understand the proposed signal transduction pathway involving the presumed redox proteins RdxBH and cbb 3 cytochrome oxidase in Rhodobacter sphaeroides 2.4.1, a series of mutants lacking components of both the Prr two-component activation system and the cbb 3 -type cytochrome oxidase or RdxBH were constructed. We report that under highly aerobic conditions, aberrant photosynthesis gene expression and spectral complex formation typical of cbb 3 - or RdxBH-deficient mutants were no longer observed when either prrA (encoding the response regulator of the Prr system) or prrB (encoding the presumed sensor kinase) was also deleted. These double-mutant strains are phenotypically identical to single-mutant PrrA and PrrB strains, suggesting that the signal(s) originating from the cbb 3 terminal oxidase affects downstream puc and puf operon expression by acting exclusively through the Prr system. When the same double-mutant strains were examined under anaerobic dark dimethyl sulfoxide growth conditions, photosynthesis gene expression was obligatorily linked to the two-component activation system. However, photosynthesis gene expression under the same growth conditions was significantly higher in the cbb 3 mutant strain when compared to that in the wild type. Similarly, under anaerobic photosynthetic conditions the high levels of the oxidized carotenoid, spheroidenone, which accumulate in cbb 3 -deficient mutants were nearly restored to normal in a PrrB − CcoP − double mutant. This observation, together with previously published results, suggests that the regulation of the CrtA-catalyzed reaction possesses both transcriptional and posttranscriptional regulatory effectors. We propose that the cbb 3 cytochrome oxidase, which by definition can interact with external oxygen, serves to control the activity of the Prr two-component activation system under both aerobic and anaerobic conditions. Although independent from the cbb 3 oxidase, the RdxBH proteins are also required for normal functioning of the Prr two-component activation system and are therefore believed to lie between the cbb 3 oxidase in this oxygen-sensing, redox signaling pathway and the Prr activation system.