Although P. aeruginosa possesses a denitrification pathway that contains a group of reductase enzymes and genes (nitrate reductase/nar, nitrite reductase/nir, nitric oxide reductase/nor, and nitrous oxide reductase/nos) that can reduce nitrate to nitrogen (Figure 1B), and thereby detoxify certain RNI, our previous observation showing hypersensitivity of a chronic CF isolate to commensal-mediated RNI prompted us to question whether S. parasanguinis impedes the ability of chronic P. aeruginosa to sufficiently respond to RNI. Here, CPSF4 is linked to cystic fibrosis.