The present study was carried out to clarify the taxonomic assignment of two closely related Spiroplasma species. Genomic information for 26 type strains was available at the time of conducting this analysis. Our analysis showed that two species, viz. Spiroplasma atrichopogonis (Koerber et al. 2005) and Spiroplasma mirum (Tully et al. 1982), are conspecific. The 16S rRNA gene sequences of the two species possess 99.78% sequence similarity. Furthermore, whole-genome sequence comparisons showed that S. atrichopogonis GNAT3597T (CP011855.1) GCA 001029245.1 and S. mirum ATCC 29335T (CP002082.1) GCA 000517365.1 shared 99.99% average nucleotide identity, 99.99% average amino acid identity and 100% digital DNA-DNA hybridization values. These values exceed the threshold values for bacterial species delineation, indicating that they belong to the same species. Furthermore, the phylogenomic analysis based on the core proteome of the strains under study confirmed that S. atrichopogonis GNAT3597T (CP011855.1) GCA 001029245.1 and S. mirum ATCC 29335T (CP002082.1) GCA 000517365.1 formed a monophyletic clade. Based on this evidence, we propose the reclassification of S. atrichopogonis Koerber et al. 2005 as a later heterotypic synonym of S. mirum Tully et al. 1982.
Keywords: Spiroplasma; heterotypic synonym; overall genome-relatedness indices; reclassification.