Two novel actinobacterial strains, designated as E257T and K478T, were isolated from hyper-arid soil samples collected in Cholistan Desert, Pakistan. Comparative analysis of 16S rRNA genes showed that strains E257T and K478T were assigned to the genus Motilibacter, being their closest relative M. rhizosphaerae RS-16T with 97.3% and 96.7% similarities, respectively. The sequence similarity between strain E257T and K478T was 98.9%. Phylogenetic analysis based on 16S rRNA gene sequences and phylogenomic analysis based on multiple genes of conserved core proteins exhibited that these two strains belonged to the genus Motilibacter and formed a robust cluster separated from the two type species of the genus Motilibacter. Average Nucleotide Identity (ANI), Average Amino acid Identity (AAI), digital DNA-DNA hybridization (dDDH) values and Percentage of Conserved Proteins (POCP) calculated from the complete genome sequences indicated strains E257T and K478T were assigned into genus Motilibacter but clearly separated from each other and from the other species of the genus Motilibacter with values below the thresholds for species delineation. The two isolates were found to have chemotaxonomic, cultural and morphological properties consistent with their classification in the genus Motilibacter and also confirmed the differentiation from their closest species. The obtained results demonstrated that strains E257T and K478T represent two novel species of the genus Motilibacter, for which the names Motilibacter desertisp. nov. (type strain E257T = JCM 33651T = CGMCC 1.17159T) and Motilibacter aurantiacus sp. nov. (type strain K478T =JCM 33652T =CGMCC 1.17229T) are proposed.
Keywords: Actinobacteria; Genome comparison; Motilibacter; Phylogeny; Taxonomy.
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