Analysis of recombinase A (recA/RecA) in the actinobacterial family Streptosporangiaceae and identification of molecular signatures.

The family Streptosporangiaceae (suborder Streptosporangineae) comprises 13 genera and 100 species with validly published names. In a recent study, gyrB gene sequences were obtained for members of the family Streptosporangiaceae and the GyrB amino acid sequences were analysed for molecular signatures. In this study, recA gene sequences (895nt) were determined for the type strains of members of the family Streptosporangiaceae. The sequences used represent 81% of the full-length recA gene of Streptosporangium roseum DSM 43021(T). The recA gene sequences were used for phylogenetic analyses and the trees were compared to the corresponding 16S-rRNA and gyrB gene trees. RecA amino acid alignments (298 amino acids) were generated and inspected for unique amino acid signatures to distinguish the genera in the family from each other. As was observed for the gyrB gene trees, the recA gene trees generally supported the division of the members of the family Streptosporangiaceae into 13 genera. The genus Nonomuraea was not monophyletic in any of the recA gene trees, while the genera Planomonospora and Streptosporangium were not monophyletic in the maximum likelihood and maximum parsimony trees. The gyrB-recA concatenated-gene tree was more robust than the recA gene tree, with 63 nodes in the gyrB-recA tree having bootstrap values ≥95%. The only insertions in the recA gene sequences were inteins identified in the type strains of Acrocarpospora phusangensis, Acrocarpospora pleiomorpha and Microbispora mesophila. Examination of the RecA sequence alignments for genus-specific amino acid sequences showed that the genera Herbidospora, Planobispora, Planomonospora and Streptosporangium contain unique amino acid sequences that distinguish these genera from all other genera in the family Streptosporangiaceae. The results of this investigation extend the results of the GyrB study and will be useful in future taxonomic studies in the family Streptosporangiaceae by providing additional genus-specific molecular signatures.