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

The present study used whole-genome data to clarify the taxonomic assignment of two closely related <i>Williamsia</i> 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 <i>Williamsia muralis</i> Kämpfer <i>et al</i>. 1999 and <i>Williamsia marianensis</i> Pathom-aree <i>et al</i>. 2006. The 16S rRNA gene sequences showed 99 % similarity between these type strains. Whole-genome-based comparisons showed that <i>Williamsia muralis</i> DSM 44343^T and <i>Williamsia marianensis</i> DSM 44944^T 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 <i>Williamsia muralis</i> DSM 44343^T and <i>Williamsia marianensis</i> DSM 44944^T formed a monophyletic clade. Based on this evidence, we propose the reclassification of <i>Williamsia marianensis</i> Pathom-aree <i>et al</i>. 2006 as a later heterotypic synonym of <i>Williamsia muralis</i> Kämpfer <i>et al</i>. 1999.