Nitric-oxide-driven oxygen release in anoxic Pseudomonas aeruginosa

Denitrification supports anoxic growth of Pseudomonas aeruginosa in infections. Moreover, denitrification may provide oxygen (O(2)) resulting from dismutation of the denitrification intermediate nitric oxide (NO) as seen in Methylomirabilis oxyfera. To examine the prevalence of NO dismutation we studied O(2) release by P. aeruginosa in airtight vials. P. aeruginosa rapidly depleted O(2) but NO supplementation generated peaks of O(2) at the onset of anoxia, and we demonstrate a direct role of NO in the O(2) release. However, we were not able to detect genetic evidence for putative NO dismutases. The supply of endogenous O(2) at the onset of anoxia could play an adaptive role when P. aeruginosa enters anaerobiosis. Furthermore, O(2) generation by NO dismutation may be more widespread than indicated by the reports on the distribution of homologues genes. In general, NO dismutation may allow removal of nitrate by denitrification without release of the very potent greenhouse gas, nitrous oxide.