Genome-based reclassification of Williamsia marianensis as a later heterotypic synonym of Williamsia muralis

Abstract

The present study used whole-genome data to clarify the taxonomic assignment of two closely related Williamsia species. Genomic information for 10 type strains was available at the time of conducting this analysis. One group of type strains was found to be conspecific, namely Williamsia muralis Kämpfer et al. 1999 and Williamsia marianensis Pathom-aree et al. 2006. The 16S rRNA gene sequences showed 99 % similarity between these type strains. Whole-genome-based comparisons showed that Williamsia muralis DSM 44343T and Williamsia marianensis DSM 44944T shared 98.07 % average nucleotide identity, 98.29 % average amino acid identity and 84.80 % digital DNA–DNA hybridization values. These values exceeded the threshold values for bacterial species delineation. Further, phylogenomic analysis based on the core genomes of the strains under study confirmed that Williamsia muralis DSM 44343T and Williamsia marianensis DSM 44944T formed a monophyletic clade. Based on this evidence, we propose the reclassification of Williamsia marianensis Pathom-aree et al. 2006 as a later heterotypic synonym of Williamsia muralis Kämpfer et al. 1999.