Gyrase subunit B amino acid signatures for the actinobacterial family Streptosporangiaceae

Higher order taxonomic assignments (family level and above) in the phylum Actinobacteria are currently based only on 16S-rRNA gene sequence analyses. Additional molecular markers need to be identified to increase the number of reference points for defining actinobacterial families and other higher taxa. Furthermore, since most novel actinobacterial taxa are defined at the level of species and genera, it is necessary to define molecular signatures at the genus level to enhance the robustness of genus descriptions. The current use of chemotaxonomic markers to define genera could be improved by the identification of genus-specific molecular signatures. In this study, GyrB amino acid sequences for members of the family Streptosporangiaceae were analysed for molecular signatures. Phylogenetic analyses showed that the gyrB gene tree supported the composition of the currently recognised genera in this family. The catalytically important amino acids were identified in the GyrB sequences, as were the GHKL superfamily motifs. Examination of GyrB protein sequence alignments revealed that there are genus-specific sequences for most of the multi-species genera and genus-defining amino acid insertions for the genera Herbidospora and Microbispora. Furthermore, there are GyrB signature amino acids which distinguish the family Streptosporangiaceae from the family Nocardiopsaceae.