Ruicaihuangia ninglii sp. nov., Ruicaihuangia jiafui sp. nov. and Homoserinibacter chengtaonis sp. nov., three new members of the family Microbacteriaceae isolated from the Qinghai–Tibet Plateau, China

Six novel strains (LJ205^T, TR449, ZJ450^T, ZJ454, ZJ70^T and ZJ77) were isolated from the Qinghai-Tibet Plateau, China, representing three distinct novel species. The cells were Gram-stain-positive, oxidase-negative, catalase-positive and rod-shaped. Strains LJ205^T and TR449 were strictly aerobic, whereas strains ZJ450^T, ZJ454, ZJ70^T, and ZJ77 were facultatively anaerobic. Strains LJ205^T and TR449 grew optimally at 28.0 °C, pH 9.0 and 0.5-1.0% (w/v) NaCl, whereas strains ZJ450^T, ZJ454, ZJ70^T and ZJ77 showed optimal growth at 28.0 °C, pH 7.0 and 1.0% (w/v) NaCl. Comparative analysis of 16S rRNA gene sequences revealed that all six strains belonged to the family <i>Microbacteriaceae</i> and represented three distinct species. Phylogenetic analysis based on 675 core genes further confirmed that the 6 isolates formed 3 well-separated clades within the family <i>Microbacteriaceae</i>. The DNA G+C contents of the type strains LJ205^T, ZJ450^T and ZJ70^T of the three novel species are 66.5, 66.7 and 69.1 mol%, respectively. Digital DNA-DNA hybridization and average nucleotide identity analyses confirmed that the three type strains represent distinct novel species. Strains LJ205^T and ZJ70^T contained cell-wall amino acids Ala, Glu, Gly, Lys and DAB, while ZJ450^T had Ala, Glu, Gly and Orn. Their major menaquinones were MK-13, MK-12 and MK-14 in LJ205^T and ZJ70^T, but only MK-14 and MK-13 in ZJ450^T. Polar lipids included diphosphatidylglycerol, phosphatidylglycerol and glycolipid in LJ205^T and ZJ450^T, with ZJ70^T containing an additional phospholipid. Based on genotypic, phenotypic, phylogenetic and biochemical properties, the six novel strains are grouped into three distinct lineages, each represented by a type strain, and thus constitute three novel species in the family <i>Microbacteriaceae</i>, for which the names <i>Ruicaihuangia ninglii</i> sp. nov. (type strain LJ205^T=CGMCC 1.17451^T=JCM 33727^T), <i>Ruicaihuangia jiafui</i> sp. nov. (type strain ZJ450^T=GDMCC 1.1955^T=KCTC 49508^T) and <i>Homoserinibacter chengtaonis</i> sp. nov. (type strain ZJ70^T=GDMCC 1.1954^T=KCTC 49509^T) are proposed, respectively.