A phylogeny of the genus Nocardia deduced from the analysis of small-subunit ribosomal DNA sequences, including transfer of Nocardia amarae to the genus Gordona as Gordona amarae comb. nov.

According to phylogenetic analyses of nearly complete small-subunit ribosomal DNA sequences, the genus Nocardia should not comprise the two species Nocardia petroleophila and Nocardia amarae. N. amarae should be reassigned to the genus Gordona as Gordona amarae. All of the other Nocardia species form a monophyletic unit, closely related to species of the genus Rhodococcus. It is proposed to revive the name 'CMN' to comprise the genera Corynebacterium, Tsukamurella, Mycobacterium, Gordona, Rhodococcus and Nocardia that form a well identified and monophyletic unit. They are all characterized by a cell wall chemotype IV with mycolic acids.