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Phylogenetic studies of genus Nocardia species based on gyrB gene analyses

¹ Medical Mycology Research Center, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba;

² Chiba University

³ E-mail: gonoi{at}faculty.chiba-u.jp

Received March 24, 2009
Accepted October 8, 2009

Phylogenetic analyses of 56 type species of Nocardia were conducted using the partial nucleotide sequences of gyrase B (gyrB) gene. The interspecies similarities of gyrB gene for 56 type species of Nocardia are 82.4-99.9%, which correspond to 270-2 nucleotide differences in the partial gene sequences around 1,200 bp. In comparison to phylogenetic relations, gyrB gene sequence information is generally consistent with that of 16S rRNA gene sequences with minor exceptions. However, the degree of divergence of gyrB gene sequences is approximately 3.6 times greater than that of 16S rRNA gene sequences, suggesting a higher discriminative power of gyrB sequence information than that of 16S rRNA within the species of Nocardia. Nocardia type species are clustered based on gyrB sequence similarity values of 93.5% and above. Among the 56 type species, 37 species are distributed into 13 clusters, each comprising 2-7 species. The remaining 19 species are classified into an independent cluster, in which the similarities between each species and other 55 Nocardia species are lower than 93.5%. Among the eight mycolic-acid-containing actinomycete genera in the suborder Corynebacterineae, Nocardia was clearly differentiated from other actinomycete genera such as Rhodococcus by gyrB gene analyses (similarity values of gyrB sequences of Nocardia and Rhodococcus are 75-85%), indicating that gyrB gene is a useful alternative to 16S rRNA gene for determination of phylogenetic relations between the genus Nocardia and seven other actinomycete genera.