Comammox genomes encode a very energy efficient pathway for guanidine conversion regulated by a guanidine riboswitch. We showed with Nitrospira inopinata that it is the first described organism capable of growing on guanidine as source of energy, reductant, & nitrogen

Phylogenetic analyses revealed that use of guanidine is an ancient trait of comammox microbes suggesting that it confers a selective advantage to comammox strains and has therefore been retained in their genomes during evolution