Nocardia sichangensis sp. nov., isolated from rocky soil of Sichang Island

A novel actinobacterium, designated strain SC052^T, was isolated from rocky soil collected from Sichang Island, Chonburi Province, Thailand. Morphological and chemotaxonomic analyses indicated that strain SC052^T belongs to the genus <i>Nocardia</i>. The strain exhibited extensively branched substrate mycelia and produced short chains of four to six spores on the aerial mycelia. The cell wall contained <i>meso</i>-diaminopimelic acid, while ribose, arabinose, glucose and galactose were detected in the whole-cell hydrolysate. The identified polar lipids included diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, one unidentified glycolipid, two unidentified lipids and three unidentified phospholipids. The menaquinone was MK-8 (H4<i>ω</i>-cycl). The major cellular fatty acids included C_16:0, C_17:0, C_18:0, 10-methyl C_18:0 tuberculostearic acid, C_18:1 <i>ω</i>9c, summed feature 3 and summed feature 6. Mycolic acids were also detected. A blast search of the 16S rRNA gene sequence revealed that strain SC052^T exhibited the highest similarity (99.7%) to <i>Nocardia araoensis</i> NBRC 100135^T. Phylogenetic analysis based on the <i>gyrB</i> gene and phylogenomic tree construction further supported that <i>N. araoensis</i> NBRC 100135^T is the closest phylogenetic neighbour of strain SC052^T. Comparative genomic analyses between strain SC052^T and <i>N. araoensis</i> NBRC 100135^T revealed digital DNA-DNA hybridization values of 47.9% and average nucleotide identity values of 91.5% (ANIb) and 92.8% (ANIm), all of which fall below the threshold used to delineate strains of the same species. Based on phenotypic and genomic analyses, strain SC052^T is proposed as a novel species within the genus <i>Nocardia</i>, for which the name <i>Nocardia sichangensis</i> sp. nov. is proposed (=TBRC 14541^T, =NBRC 115195^T).