Member of this ferredoxin-like protein family are found exclusively in species with an operon encoding the cbb3 type of cytochrome c oxidase (cco-cbb3), and near the cco-cbb3 operon in about half the cases. The cco-cbb3 is found in a variety of proteobacteria and almost nowhere else, and is associated with oxygen use under microaerobic conditions. Some (but not all) of these proteobacteria are also nitrogen-fixing, hence the gene symbol fixG. FixG was shown essential for functional cco-cbb3 expression in Bradyrhizobium japonicum.
Jiyao W et al.(2023). "The conserved domain database in 2023.",