The reduction of nitrous oxide to dinitrogen by Escherichia coli

Escherichia coli K12 reduces nitrous oxide stoichiometrically to molecular nitrogen with rates of 1.9 mol/h x mg protein. The activity is induced by anaerobiosis and nitrate. N₂+formation from N₂O is inhibited by C₂H₂ (K _i 0.03 mM in the medium) and nitrite (K _i=0.3 mM) but not by azide. A mutant defective in FNR synthesis is unable to reduce N₂O to N₂. The reaction in the wild type could routinely be followed by gas chromatography and alternatively by mass spectrometry measuring the formation of ¹⁵N₂ from ¹⁵N₂O. The enzyme catalyzing N₂O-reduction in E. coli could not be identified; it is probably neither nitrate reductase nor nitrogenase. E. coli does not grow with N₂O as sole respiratory electron acceptor. N₂O-reduction might not have a physiological role in E. coli, and the enzyme involved might catalyze something else in nature, as it has a low affinity for the substrate N₂O (apparent K _m3.0 mM). The capability for N₂O-reduction to N₂ is not restricted to E. coli but is also demonstrable in Yersinia kristensenii and Buttiauxella agrestis of the Enterobacteriaceae. E. coli is able to produce NO and N₂O from nitrite by nitrate reductase, depending on the assay conditions. In such experiments NO _inf2 ^sup- is not reduced to N₂ because of the high demand for N₂O of N₂O-reduction and the inhibitory effect of NO _inf2 ^sup- on this reaction.Dedicated to Professor L. Jaenicke, Köln, on the occassion of his 70th birthday