Comparison of gyrB gene sequences, 16S rRNA gene sequences and DNA–DNA hybridization in the Bacillus subtilis group

The Bacillus subtilis group comprises eight closely related species that are indistinguishable from one another by 16S rRNA gene sequence analysis. Therefore, the gyrB gene, which encodes the subunit B protein of DNA gyrase, was selected as an alternative phylogenetic marker. To determine whether gyrB gene sequence analysis could be used for phylogenetic analysis and species identification of members of the B. subtilis group, the congruence of gyrB grouping with both 16S rRNA gene sequencing and DNA-DNA hybridization data was evaluated. Ranges of gyrB nucleotide and translated amino acid sequence similarities among the eight type strains were 75.4-95.0 % and 88.5-99.2 %, respectively, whereas 16S rRNA gene sequence similarities were 98.1-99.8 %. Results showed that gyrB gene sequences provide higher resolution than 16S rRNA gene sequences. The classification achieved by gyrB sequence analysis was in agreement with results obtained with DNA-DNA hybridization. It is concluded that the gyrB gene may be an efficient alternative target for identification and taxonomic analysis of members of the B. subtilis group.