Comparative genome analysis using whole genome sequences suggests ongoing speciation between Priestia aryabhattai and Priestia megaterium

Introduction Priestia megaterium and P. aryabhattai are closely related bacteria of industrial relevance whose species status has been debated. Previous studies have not sufficiently resolved this taxonomic issue. Methods To clarify the taxonomy of these two species, we compared 190 publicly available genomes, including 12 new high-quality assemblies. In addition, metagenomic and phenotypic data were examined for species-level differences. Results Whole-genome phylogenies consistently resolved two monophyletic clades corresponding to the named taxa. Mean digital DNA–DNA hybridization between the clades was 64%, supporting separation at the species level, whereas the mean average nucleotide identity was 95.2%, indicative of an ambiguous boundary-range. Several newly isolated strains showed recombinant genomic signatures, suggesting gene flow during an ongoing speciation. Metagenomic surveys indicated distinct ecological patterns, with differences in abundance across tropical and temperate regions. Using complete assemblies, we identified species-specific loci and designed PCR primers capable of discriminating the two taxa. Discussion Our results support the taxonomic classification of P. megaterium and P. aryabhattai as distinct species and provide novel molecular markers to facilitate ecological, industrial, and diagnostic studies.