nosZ

NosZ, or nitrous oxide reductase, is a copper-containing enzyme that catalyzes the final step of the microbial denitrification pathway, converting nitrous oxide (N2O) to dinitrogen (N2). The chemical reaction is N2O + 2 e− + 2 H+ → N2 + H2O. The enzyme is encoded by the nosZ gene and is often part of a larger nos operon that includes genes required for maturation and assembly of the catalytic site, such as nosD, nosF, and nosL. In many Gram-negative bacteria, NosZ is localized to the periplasm and relies on copper centers at the active site for its catalytic activity.

Diversity and classification: NosZ exists in two major phylogenetic clades. Clade I comprises the typical NosZ enzymes found in many canonical denitrifiers, while clade II consists of atypical NosZ enzymes that are present in a broader range of organisms, including some that do not possess the full set of denitrification genes. Atypical NosZ can expand the capacity for N2O reduction beyond classical denitrifiers and often exhibits different maturation requirements and cellular localization.

Ecological and environmental significance: NosZ is widespread among bacteria and archaea in soils, sediments, wastewater systems, and marine environments. By reducing N2O to N2, NosZ helps mitigate emissions of nitrous oxide, a potent greenhouse gas and ozone-depleting substance. Because the distribution and expression of nosZ influence N2O fluxes, NosZ is a focus of research on strategies to reduce N2O emissions in agricultural and engineered systems.