Dunn AK, Karr EA, Wang Y, Batton AR, Ruby EG, Stabb EV
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The alternative oxidase (AOX) gene in Vibrio fischeri is controlled by NsrR and upregulated in response to nitric oxide.
Mol Microbiol. 2010 Jul 1;77(1):44-55
Authors: Dunn AK, Karr EA, Wang Y, Batton AR, Ruby EG, Stabb EV
Alternative oxidase (AOX) is a respiratory oxidase found in certain eukaryotes and bacteria; however, its role in bacterial physiology is unclear. Exploiting the genetic tractability of the bacterium Vibrio fischeri, we explore the regulation of aox expression and AOX function. Using quantitative PCR and reporter assays, we demonstrate that aox expression is induced in the presence of nitric oxide (NO), and that the NO-responsive regulatory protein NsrR mediates the response. We have identified key amino acid residues important for NsrR function and experimentally confirmed a bioinformatically predicted NsrR binding site upstream of aox. Microrespirometry demonstrated that oxygen consumption by V. fischeri CydAB quinol oxidase is inhibited by NO treatment, whereas oxygen consumption by AOX is less sensitive to NO. NADH oxidation assays using inverted membrane vesicles confirmed that NO directly inhibits CydAB, and that AOX is resistant to NO inhibition. These results indicate a role for V. fischeri AOX in aerobic respiration during NO stress.
PMID: 20487270 [PubMed - in process]
This is an interesting paper that proposes the alternative nitric-oxide insensitive respiratory oxidase (aox) of Vibrio fischeri as a key metabolic adaptation to ensure mono-colonization of the squid light organ, excluding other NO-sensitive bacteria. Previous work showed that V. fischeri excludes other marine bacteria from the light organ by unknown mechainsms, and that NO production by the squid was an important aspect of V. fischeri colonization. NO can inhibit respiration by heme-containing oxidases, so NO-sensitive bacteria would exhibit decreased fitness.
I would have liked to see the affects of NO on growth of the wildtype vs. aox mutant, rather than just oxygen consumption as a measure of respiration. Apparently these experiments were performed, but were “data not shown”. The authors also did not test their aox mutant in a colonization assay of the squid, although perhaps these are experiments in progress.
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