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 Y1685T, Y1700, Y2011T and Y2014 shared the highest similarity (95.12-95.33%) with Enemella dayhoffiae NML 130396T. 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 Propionibacteriaceae. The strains Y1685T, Y1700, Y2011T 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 Y1685T and Y2011T. The major fatty acids of strain Y1685T were iso-C15 : 0, anteiso-C15 : 0 and iso-C16 : 0, while the major fatty acids of strain Y2011T were iso-C15 : 0 and anteiso-C15 : 0. The cell-wall sugars of strain Y1685T were ribose and rhamnose, and the cell-wall amino acids were alanine, glutamic acid, glycine and ll-diaminopimelic acid. In contrast, strain Y2011T 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 Propionibacteriaceae. We proposed the genus Carbonicoccus gen. nov., with the type species Carbonicoccus zhangzhihongae sp. nov. (type strain Y1685T=KCTC 59535T=GDMCC 1.5547T) and Carbonicoccus niuqiaonis sp. nov. (type strain Y2011T=KCTC 59536T=GDMCC 1.5548T).