Effect of acetylene on autotrophic and heterotrophic nitrification

Abstract

Acetylene (C₂H₂) strongly inhibited (K_i 0.25 μM or 0.66 Pa) the oxidation of ammonia (NH₄⁺) to nitrite (NO₂⁻) by Nitrosomonas europaea but did not affect the oxidation of hydroxylamine (NH₂OH) to NO₂⁻ by this organism. We suggest that the C₂H₂-sensitive step is associated with the ammonia oxygenase. Oxidation of NH₄⁺ was inhibited only approximately 50% by 0.4 mM (10 kPa) ethylene and by 2.1 mM (10 kPa) nitrous oxide and was unaffected by 0.1 mM (10 kPa) methane. The oxidation of NO₂⁻ to nitrate (NO₃⁻) by Nitrobacter winogradskyi and of NH₄⁺ to NH₂OH and NO₃⁻ by the heterotrophic nitrifier, Arthrobacter sp., was not affected by 3.83 mM (10 kPa) C₂H₂.