Thioclava arctica sp. nov. and Zhongshania arctica sp. nov., isolated from the surface sediment of the Arctic Ocean and reclassification of Marortus luteolus Yu et al. 2019 as a later heterotypic synonym of Zhongshania marina On et al. 2019

Two Gram-stain-negative bacterial strains, 15-R06ZXC-3^T and R06B22^T, were isolated from the surface sediment of the Arctic Ocean. Phylogenetic analyses based on the 16S rRNA gene and genome sequences indicated that strain 15-R06ZXC-3^T belongs to the genus <i>Thioclava</i>, while strain R06B22^T belongs to the genus <i>Zhongshania</i>. Strain 15-R06ZXC-3^T showed the closest relationship to <i>Thioclava indica</i> DT23-4^T. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strain 15-R06ZXC-3^T and all of the type strains of the genus <i>Thioclava</i> ranged from 20.8 to 30.4% and 79.1 to 85.7%, respectively. Strain R06B22^T was most closely related to <i>Zhongshania marina</i> DSW25-10^T. The dDDH and ANI values between strain R06B22^T and all of the type strains of the genus <i>Zhongshania</i> ranged from 18.6 to 20.4% and 77.5 to 79.4%, respectively. These dDDH and ANI values were all below the standard cutoff criteria for the delineation of bacterial species, indicating that the two strains may represent novel species within their respective genera. Furthermore, their phenotypic and chemotaxonomic characteristics also differentiated them from closely related species. Based on the polyphasic analyses, strains 15-R06ZXC-3^T and R06B22^T separately represent novel species of the genera <i>Thioclava</i> and <i>Zhongshania</i>, for which the names <i>Thioclava arctica</i> sp. nov. (type strain 15-R06ZXC-3^T = MCCC 1A07434^T= KCTC 8342^T) and <i>Zhongshania arctica</i> sp. nov. (type strain R06B22^T = MCCC 1A08273^T= KCTC 8343^T) are proposed. Additionally, phylogenomic analyses showed that the strain <i>Marortus luteolus</i> ZX-21^T was clustered with the strain <i>Z. marina</i> DSW25-10^T and all other type strains of the genus <i>Zhongshania</i>. Furthermore, the ANI and dDDH values between strains ZX-21^T and DSW25-10^T were 97.6% and 78.8±2.5%, respectively, strongly indicating that they represented a single species. Therefore, it is proposed that <i>M. luteolus</i> Yu <i>et al.</i> 2019 be recognized as a later heterotypic synonym of <i>Z. marina</i> On <i>et al.</i> 2019.