Temporary low oxygen conditions for the formation of nitrate reductase and nitrous oxide reductase by denitrifying Pseudomonas sp. G59

Abstract

Formation of nitrate reductase (NaR) and nitrous oxide reductase (N₂OR) by a Pseudomonas sp. G59 did not occur in aerobic or anaerobic conditions, but was observed in a microaerobic incubation in which an anaerobically grown culture was agitated in a sealed vessel initially containing 20 kPa oxygen in the headspace. During the microaerobic incubation, the oxygen concentration in the headspace decreased and dissolved oxygen reached 0.1–0.2 kPa. NaR activity was detected immediately and N₂OR activity after 3 h of incubation irrespective of the presence or absence of NO₃⁻ or N₂O. In the presence of NO₃⁻, NO₂⁻ was accumulated as a major product, but N₂O was observed in low concentrations only after N₂OR appeared. After microaerobic incubation for 3 h, N₂OR formation continued even anaerobically in an atmosphere of N₂O. In contrast, Escherichia coli formed NaR not only microaerobically but also anaerobically. However, NaR formation by E. coli was inhibited by sodium fluoride under anaerobic, but not under microaerobic conditions. The Pseudomonas culture did not possess fermentative activity. It is suggested that the dependence on microaerobiosis for the formation of these reductases by the Pseudomonas culture was due to an inability to produce energy anaerobically until these anaerobic respiratory enzymes were formed.