Bioenergetics at extreme temperature: Thermus thermophilus ba3- and caa3-type cytochrome c oxidases

► T. thermophilus ba3- and caa3-type cytochrome c oxidases have evolved separately. ► The subunits of caa3-oxidase and its heme insertion factor are fused. ► The fused genes are phylogenetically ancient. ► The subunit IV of caa3- and aa3-oxidases is not evolutionarily conserved. ► The ba3-oxidase has certain structural features dissimilar to aa3-oxidases.