A comparison of 16S rRNA gene sequences between Peribacillus frigoritolerans DSM 8801 T and Peribacillus castrilensis N3T revealed 99.9% sequence similarity, suggesting their close relatedness and the possibility of these strains belonging to the same species. The genus Peribacillus includes 21 species with validly published names. The type species P. frigoritolerans DSM 8801T (=ATCC 25097T=CCUG 43489T=CIP 67.20T=JCM 11681T) was isolated from arid soil in Morocco, while P. castrilensis N3T (=CECT 30509T=LMG 32505T) was isolated from the faeces of a river otter in Castril (Granada, southern Spain). The present study used whole-genome data to clarify the taxonomic assignment of these two closely related Peribacillus species. P. frigoritolerans DSM 8801T and P. castrilensis N3T share similar chemotaxonomic and phenotypic characteristics. Their main cellular fatty acids were anteiso-C15 : 0 and iso-C15 : 0. Overall genomic relatedness indices analyses indicated that P. frigoritolerans DSM 8801T and P. castrilensis N3T shared average nucleotide identity and digital DNA-DNA hybridization values >95% and >70%, which are the currently accepted thresholds for species-level delineation. Additionally, these taxa formed a tight cluster within the genus Peribacillus in both the 16S rRNA gene phylogenetic tree and the core-genome phylogenomic tree. Based on the combined evidence and the earliest valid publication, priority is given to P. frigoritolerans (Delaporte and Sasson 1967) Montecillo and Bae 2022. Peribacillus castrilensis Rodríguez et al. 2023 is proposed to be a later heterotypic synonym of P. frigoritolerans (Delaporte and Sasson 1967) Montecillo and Bae 2022.
Keywords: Peribacillus; Peribacillus castrilensis; Peribacillus frigoritolerans; genome; heterotypic synonym; taxonomy.