1887

Abstract

aerobically respires with several terminal oxidases. The quinol oxidase (Cyo) encoded by is needed for efficient adaptation to low oxygen conditions and transcription is upregulated at low oxygen. This study sought to determine how transcription of the operon is regulated. The 5′ sequence upstream of was analysed and revealed putative binding sites for ActR of the ActSR two-component regulatory system. The expression of was decreased in an mutant regardless of the oxygen condition. As ActSR is known to be important for growth under low pH in another rhizobial species, the effect of growth medium pH on expression was tested. As the pH of the media was incrementally decreased, expression gradually increased in the WT, eventually reaching ∼10-fold higher levels at low pH (4.8) compared with neutral pH (7.0) conditions. This upregulation of under decreasing pH conditions was eliminated in the mutant. Both the and mutants had severe growth defects at low pH (4.8). Lastly, the and mutants had severe growth defects when grown in media treated with an iron chelator. Under these conditions, was upregulated in the WT, whereas was not induced in the mutant. Altogether, the results indicated expression is largely dependent on the ActSR two-component system. This study also demonstrated additional physiological roles for Cyo in CFN42, in which it is the preferred oxidase for growth under acidic and low iron conditions.

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2015-09-01
2024-10-03
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