Probably functions as a FAD-dependent oxidoreductase, whose physiological substrate is unknown. Does not display amino-acid oxidase or glycerol-3-phosphate dehydrogenase activities (PubMed:26841760). Is essential for growth of P.aeruginosa in the sputum of cystic fibrosis patients (PubMed:25775563). Binds 1 FAD per subunit. Monomer. Cells lacking this gene show growth defect in natural and synthetic cystic fibrosis sputum. Belongs to the DAO family.