Disruption of narG, the Gene Encoding the Catalytic Subunit of Respiratory Nitrate Reductase, Also Affects Nitrite Respiration in Pseudomonas fluorescens YT101

The Pseudomonas fluorescens YT101 gene narG, which encodes the catalytic α subunit of the respiratory nitrate reductase, was disrupted by insertion of a gentamicin resistance cassette. In the Nar(−) mutants, nitrate reductase activity was not detectable under all the conditions tested, suggesting that P. fluorescens YT101 contains only one membrane-bound nitrate reductase and no periplasmic nitrate reductase. Whereas N(2)O respiration was not affected, anaerobic growth with NO(2) as the sole electron acceptor was delayed for all of the Nar(−) mutants following a transfer from oxic to anoxic conditions. These results provide the first demonstration of a regulatory link between nitrate and nitrite respiration in the denitrifying pathway.