Multiheme hydroxylamine oxidoreductases produce NO during ammonia oxidation in methanotrophs
Wouter Versantvoort, Arjan Pol, Mike S. M. Jetten, Laura van Niftrik, Joachim Reimann, Boran Kartal, Huub J. M. Op den Camp
Abstract
Significance Methanotrophs oxidize methane to CO 2 , thereby mitigating the emission of this potent greenhouse gas. Understanding how these microorganisms are influenced by anthropogenic activities will help better predict their impact on global warming and utilize them to reduce it. Ammonia-fertilizer input to the environment has greatly improved crop yields but increased emissions of greenhouse gasses like N 2 O as well. In methane-rich environments, methanotrophs play a prominent role in ammonia oxidation. Here, we purified a protein (mHAO) from Methylacidiphilum fumariolicum , capable of rapid oxidation of hydroxylamine to NO. We propose that mHAO enables methanotrophs to cope with high ammonia concentrations, leading to reduced methane emissions. However, this activity simultaneously contributes to ammonia loss and nitrite production, and potentially leads to N 2 O emissions.