The anaerobically induced sRNA PaiI affects denitrification in Pseudomonas aeruginosa PA14

Pseudomonas aeruginosa is an opportunistic pathogen that can thrive by anaerobic respiration in the lungs of cystic fibrosis patients using nitrate as terminal electron acceptor. Here, we report the identification and characterization of the small RNA PaiI in the P. aeruginosa strain 14 (PA14). PaiI is anaerobically induced in the presence of nitrate and depends on the two-component system NarXL. The sRNA is stable during anaerobiosis and rapidly degraded in the presence of oxygen. Our studies further revealed that PaiI is required for efficient denitrification affecting the conversion of nitrite to nitric oxide. In the absence of PaiI anaerobic growth was impaired on glucose as the sole carbon source. This phenotype was suppressed by overproduction of the transcriptional regulator Dnr, which is required for transcription of genes encoding the denitrification machinery. The importance of PaiI for anaerobic growth was further underlined by the observation that a paiI deletion mutant displayed an impaired growth in the hypoxic/anaerobic necrotic centers of transplanted subcutaneous mouse tumors. This data are discussed in terms of a model wherein PaiI either directly or indirectly impacts on the denitrification pathway.