nxrC

nxrC is a gene name used in microbiology to denote a protein subunit associated with nitrite oxidoreductase (NXR), the enzyme complex that catalyzes the oxidation of nitrite to nitrate in nitrite-oxidizing bacteria. In many genomes, nxrC is co-located with nxrA and nxrB, which encode the catalytic subunits of NXR, forming the nxrABC operon. The NXR complex accepts electrons from nitrite and transfers them to the respiratory chain, contributing to chemolithoautotrophic growth.

The precise role of nxrC varies among lineages; in several species it is proposed as a small periplasmic or membrane-associated protein that participates in electron transfer, stabilization, or assembly of the complex. In other lineages, nxrC sequences are poorly conserved and functional assignments remain uncertain.

Nx rC genes have been identified in various nitrite-oxidizing bacteria, including genera such as Nitrospira and Nitrobacter, and are often detected in metagenomes from soils, freshwater, and wastewater systems. The presence of nxrC alongside nxrA and nxrB supports its association with nitrite oxidation pathways in these organisms.

Understanding nxrC contributes to knowledge about the nitrification process and nitrogen cycling, with potential implications for environmental monitoring and biotechnological applications such as wastewater treatment. Ongoing comparative genomics and biochemical studies aim to clarify its exact function, interaction with the core NXR subunits, and how it influences enzyme assembly and activity across different nitrifying bacteria.