Production and utilization of nitrous oxide by Pseudomonas denitrificans.

Nitrous oxide has been recognized as a product of denitrifying organisms since the early work of Gayon and Dupetit (1882a, b; 1886). Under some conditions it can be the major initial product (Wijler and Delwiche, 1954). Kluyver and Verhoeven (1954) have investigated the production of nitrous oxide by a large number of denitrifiers and conclude that its production and utilization is characteristic of all denitrifiers. Sacks and Barker (1952) observed that under some conditions the utilization of nitrous oxide bv nitrate adapted cells of Pseudomonas denitrificans showed a lag, indicating that adaptation to nitrate did not necessarily include adaptation to nitrous oxide. They further observed that azide and dinitrophenol inhibited the reduction of nitrous oxide but did not affect the reduction of nitrate to nitrogen gas. On the basis of this observation they concluded that, at least for this organism, nitrous oxide was not an obligatorv intermediate. Allen and van Niel (1952) working with Pseudomonas stutzeri did observe simultaneous adaptation of this organism to nitrate and nitrous oxide. They found also that under conditions of cyanide inhibition the reduction of nitrate and nitrous oxide could be suppressed completely but the organism would still produce nitrogen from nitrite. On the basis of these findings, the conclusion is implied that nitrous oxide is not an intermediate in the production of nitrogen gas from nitrite but that it is reversibly derived from some intermediate product in the denitrification reaction. Kluyver and Verhoeven (1954) conclude that nitrous oxide normally is intermediate in the denitrification process because of the ubiquity of its occurrence, but suggest that there are two possible paths of denitrification and that an alternative direct hydrogenation of an intermediate having the empirical formula N202H2 would explain the results of Sacks and Barker (1952), and Allen and van Niel (1952). These studies of the denitrification reaction have been by manometric techniques and dependent upon the differential solubilities of nitrogen and nitrous oxide. For the experiments to be described, the exchange of gases by denitrifying organisms has been followed, using the mass spectrometer to identify gases in the reaction. The production and utilization of nitrous oxide and the formation of nitrogen have been followed with resting cell suspensions from cultures grown under various levels of nitrate, nitrite, oxygen, or nitrous oxide. In this manner it has been possible to gather further information relative to adaptation phenomena and the effect of inhibitors in this reaction.