Carbonicoccus gen. nov., Carbonicoccus zhangzhihongae sp. nov. and Carbonicoccus niuqiaonis sp. nov., novel taxa assignable to the family Propionibacteriaceae and derived from the coal mine dust samples in Shanxi Province of China

Four Gram-positive, aerobic, non-motile cocci-shaped bacteria were isolated from the coal mine dust samples collected in Yuncheng City, Shanxi Province, and subjected to polyphasic taxonomic characterization. Whole-genome sequencing revealed that genomic sizes ranged from 3.7 to 4.2 Mb, with G+C contents of 67.0-69.5 mol%. Comparative analysis of 16S rRNA gene sequences revealed that strains Y1685^T, Y1700, Y2011^T and Y2014 shared the highest similarity (95.12-95.33%) with <i>Enemella dayhoffiae</i> NML 130396^T. Phylogenetic analysis based on 16S rRNA gene sequences and 552 core genes consistently placed the 4 strains within a distinct clade, separate from recognized genera in the family <i>Propionibacteriaceae</i>. The strains Y1685^T, Y1700, Y2011^T and Y2014 exhibited optimal growth on brain heart infusion agar supplemented with 5% defibrinated sheep blood medium at 30 °C, forming convex, opaque, smooth colonies with spherical cells. All strains were oxidase-negative and catalase-positive. MK-9 (H₄) was the sole menaquinone in type strains Y1685^T and Y2011^T. The major fatty acids of strain Y1685^T were iso-C_{15 : 0}, anteiso-C_{15 : 0} and iso-C_{16 : 0}, while the major fatty acids of strain Y2011^T were iso-C_{15 : 0} and anteiso-C_{15 : 0}. The cell-wall sugars of strain Y1685^T were ribose and rhamnose, and the cell-wall amino acids were alanine, glutamic acid, glycine and ll-diaminopimelic acid. In contrast, strain Y2011^T contained arabinose, glucose and galactose as cell wall sugars, with alanine, glutamic acid and glycine as the principal amino acids. Genomic and phenotypic data collectively support the classification of these isolates as representing two novel species within a new genus of the family <i>Propionibacteriaceae</i>. We proposed the genus <i>Carbonicoccus</i> gen. nov., with the type species <i>Carbonicoccus zhangzhihongae</i> sp. nov. (type strain Y1685^T=KCTC 59535^T=GDMCC 1.5547^T) and <i>Carbonicoccus niuqiaonis</i> sp. nov. (type strain Y2011^T=KCTC 59536^T=GDMCC 1.5548^T).