Engagement of denitrification in infected CF lungs is in accordance with the production of the denitrification intermediate nitrous oxide (N2O) in sputum (Kolpen et al., 2014b), the presence of the denitrification marker OprF and antibodies against OprF in lung secretions and sera (Yoon et al., 2002), antibodies against Nar in sera (Beckmann et al., 2005) and the upregulation of the denitrification reductases in CF isolates (Son et al., 2007; Hoboth et al., 2009; Lee et al., 2011). The gene discussed is CPSF4; the disease is cystic fibrosis.