Prevalence of nitrous oxide reducing capacity in denitrifiers from a variety of habitats

Summary A total of 81 strains isolated by T. N. Gamble from soils from eight countries, fresh water lake sediments and nitrified poultry manure were examined for their ability to grow on N₂O as their electron acceptor, as well as for their tendency to produce N₂O from NO ₃ ⁻ in the absence and presence of acetylene. Seventy-seven of the 81 strains were confirmed as denitrifiers. Fifty-nine of the 77 strains grew on N₂O, while 12 strains produced N₂O but could not utilize it. Six strains reduced NO ₃ ⁻ to N₂ but could not grow on N₂O, suggesting that even if N₂O is always an intermediate product of denitrification, it is not always a freely diffusible intermediate. The organisms, however, would consume N₂O that accumulated early in growth and accumulated N₂O in the presence of acetylene. Thus the total number of N₂O users was 65 strains or 83% of the total tested. This implies that the N₂O reducing capacity of denitrifiers occur widely in nature. A high proportion ofPseudomonas fluorescens biotype II reduced N₂O. The accumulation of N₂O from NO ₃ ⁻ in the presence of acetylene provides strong evidence that N₂O is generally an intermediate in denitrification as well as provides additional support for the usefulness of this chemical as a general inhibitor of N₂O reduction.