A NosA-specific bacteriophage can be used to select denitrification-defective mutants of Pseudomonas stutzeri.

phi PS5, a double-stranded DNA bacteriophage of Pseudomonas stutzeri JM604 that adsorbs specifically to the outer-membrane protein NosA, was isolated from stagnant irrigation ditch water. Mutant strains that do not produce NosA are resistant to phi PS5 and cannot grow anaerobically with N2O as the sole electron acceptor. phi PS5 did not adsorb to nosA mutants and adsorption to the wild-type strain was reduced when cells were grown with a high concentration of copper, a condition that represses the synthesis of NosA. The isolation of spontaneous phi PS5-resistant mutants yielded strains that were clearly defective in growth on N2O at about a 10% incidence. About half of these strains could respire N2O when supplied with a high concentration of exogenous copper.