UNASSIGNED: @entity34389 aerobically respires with several terminal oxidases. The @entity9151 oxidase (Cyo) encoded by cyoABCD is needed for efficient adaptation to low @entity26 conditions, and cyo transcription is up-regulated at low @entity26 . This study sought to determine how transcription of the cyo operon is regulated. The 5' sequence upstream of cyo was analyzed in silico and revealed putative binding sites for ActR of the ActSR two-component regulatory system. The expression of cyo was decreased in an actSR mutant regardless of the @entity26 condition. Because ActSR is known to be important for growth at low pH in another rhizobial species, the effect of growth-medium pH on cyo expression was tested. As the pH of the media was incrementally decreased, cyo expression gradually increased in the wild type, eventually reaching approximately 10-fold higher levels at low pH (4.8) compared to neutral pH (7.0) conditions. This up-regulation of cyo under decreasing pH conditions was eliminated in the actSR mutant. Both the actSR and cyo mutants had severe growth defects at low pH (4.8). Lastly, the actSR and cyo mutants had severe growth defects when grown in media treated with an @entity68 chelator. In this condition, cyo was up-regulated in the wild type whereas cyo was not induced in the actSR mutant. Altogether, the results indicate cyo expression is largely dependent on the ActSR 2-component system. This study also demonstrates additional physiological roles for Cyo in @entity34388 , in which it is the preferred oxidase for growth in acidic and low @entity68 conditions.

The @entity9151 oxidase encoded by cyoABCD in XXXX is regulated by ActSR and is crucial for growth at low pH or low @entity68 conditions.

@entity34388 :: ('347834', 'Species') :: ['R. etli CFN42'] @entity9151 :: ('CHEBI:17594', 'Chemical') :: ['quinol'] @entity26 :: ('MESH:D010100', 'Chemical') :: ['oxygen'] @entity34389 :: ('29449', 'Species') :: ['Rhizobium etli'] @entity68 :: ('MESH:D007501', 'Chemical') :: ['iron']
@entity34388 :: (347834,Species) :: ['Rhizobium etli CFN42']
