Actinomadura monticuli sp. nov., isolated from Darangshi Oreum (a volcanic cone), and the reclassification of Actinomadura glauciflava Lu et al. 2003 as a later heterotypic synonym of Actinomadura luteofluorescens (Shinobu 1962) Preobrazhenskaya et a

Two mycelium-forming actinobacterial strains, designated as DLS-47 and DLS-62^T, were isolated from volcanic ash collected from the surface of a rock on the peak of Darangshi Oreum (a volcanic cone) in Jeju, Republic of Korea, and their taxonomic positions were investigated by a polyphasic approach. Both of the isolates showed growth at 20-42 °C, pH 6.0-9.0 and 0-1% (w/v) NaCl. Furthermore, DLS-47 was found to grow at 45 °C, while strain DLS-62^T grew at pH 10.0 and 3% (w/v) NaCl. The 16S rRNA gene-based phylogeny showed that both of the isolates belonged to the genus <i>Actinomadura</i>; strain DLS-47 was most closely related to <i>Actinomadura chokoriensis</i> DSM 45346^T (100% sequence identity), while strain DLS-62^T formed a tight cluster with <i>Actinomadura bangladeshensis</i> DSM 45347^T (99.5% sequence similarity). Morphological and chemotaxonomic characteristics supported the affiliation of the two isolates to the genus <i>Actinomadura</i>. Phylogenomic analysis based on 92 core gene sequences showed that both of the isolates were most closely related to <i>A. chokoriensis</i> DSM 45346^T. Strain DLS-47 shared 100% of orthologous average nucleotide identity and digital DNA-DNA hybridization values with <i>A. chokoriensis</i> DSM 45346^T, while strain DLS-62^T showed orthologous average nucleotide identity ≤89.8% and digital DNA-DNA hybridization values ≤39.4% with strain DLS-47 and members of the genus <i>Actinomadura</i>. The results of phenotypic assays and comparison of overall genomic relatedness indices support the conclusion that strain DLS-47 (= KACC 23347=DSM 116423) is a strain of <i>A. chokoriensis</i>, while strain DLS-62^T (= KACC 23345^T = DSM 116424^T) represents a new species of the genus <i>Actinomadura</i>, for which the name <i>Actinomadura monticuli</i> sp. nov. is proposed. Also, <i>Actinomadura glauciflava</i> Lu <i>et al.</i> 2003 is reclassified as a later heterotypic synonym of <i>Actinomadura luteofluorescens</i> (Shinobu 1962) Preobrazhenskaya <i>et al</i>. 1975 (Approved Lists 1980) based on analysis of overall genomic relatedness indices and phenotypic similarity.