Nocardia donostiensis sp. nov., isolated from human respiratory specimens

Three human clinical isolates (X1654, X1655, and W9944) were recovered from the sputum and bronchial washings of two patients with pulmonary infections. The 16S rRNA gene sequence analysis of the isolates showed that they share 100 % sequence similarity with each other and belong to the genus Nocardia. Close phylogenetic neighbours are Nocardia brevicatena ATCC 15333(T) (98.6 %) and Nocardia paucivorans ATCC BAA-278T (98.4 %). The in silico DNA-DNA relatedness between the isolates ranges from 96.8 to 100 % suggesting that they belong to the same genomic species. The DNA-DNA relatedness between X1654 and N. brevicatena ATCC 15333(T) is 13.3 ± 2.3 % and N. paucivorans ATCC BAA-278T is 18.95 ± 1.1 % suggesting that they do not belong to the same genomic species. Believed to represent a novel species, these isolates were further characterised to establish their taxonomic standing within the genus. Chemotaxonomic data for isolate X1654 are consistent with those described for the genus Nocardia: this isolate produced saturated and unsaturated fatty acids, tuberculostearic acid (15.9 %), the major menaquinone was MK-8 (H4cyclic), mycolic acid chain lengths ranged from 38 to 58 carbons, produced meso-diaminopimelic acid with arabinose, glucose, and galactose as the whole cell sugars. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylinositol mannosides. The DNA G+C content is 66.7 mol  %. Based on the combination of phenotypic, chemotaxonomic, and genotypic data for X1654, X1655, and W9944, we conclude that these isolates represent a novel species within the genus Nocardia for which we propose the name Nocardia donostiensis sp. nov. with X1654(T) (=DSM 46814(T) = CECT 8839(T)) as the type strain.