Suggested role of NosZ in preventing N 2 O inhibition of dissimilatory nitrite reduction to ammonium.

Importance: Dissimilatory nitrate/nitrite reduction to ammonium (DNRA) is a microbial energy-conserving process that reduces NO ₃ ^- and/or NO ₂ ^- to NH ₄ ⁺ . Interestingly, DNRA-catalyzing microorganisms possessing nrfA genes are occasionally found harboring nosZ genes encoding nitrous oxide reductases, i.e., the only group of enzymes capable of removing the potent greenhouse gas N ₂ O. Here, through a series of physiological experiments examining DNRA metabolism in one of such microorganisms, Bacillus sp. DNRA2, we have discovered that N ₂ O may delay the transition to DNRA upon an oxic-to-anoxic transition, unless timely removed by the nitrous oxide reductases. These observations suggest a novel explanation as to why some nrfA -possessing microorganisms have retained nosZ genes: to remove N ₂ O that may otherwise interfere with the transition from O ₂ respiration to DNRA.
Competing Interests: The authors declare no conflict of interest.