Angustibacter speluncae sp. nov., isolated from a lava cave stalactite

Gram-reaction-positive, strictly aerobic, motile coccoid- to rod-shaped actinobacteria, designated strains YC2-20T and YC2-19 were isolated from pieces of stalactites collected at the Yongcheon Cave in Jeju, Republic of Korea. The cells of orange-coloured colonies grew at 20-37 °C, pH 6-10 and in the absence of NaCl. In the neighbour-joining tree based on 16S rRNA gene sequences, the novel isolates formed a distant sublineage at the base of the radiation of the genus Angustibacter. The novel isolates shared identical 16S rRNA gene sequences to each other and revealed a 16S rRNA gene sequence similarity of 95.6 % to the closest relative, Angustibacter aerolatus and <95 % to other members of the family Kineosporiaceae. Albeit with a low similarity of 16S rRNA gene sequences and a distinct phylogenetic position, most of the chemotaxonomic characteristics were in agreement with those of the genus Angustibacter: meso-diaminopimelic acid as the diagnostic diamino acid in the cell wall; MK-9(H4) as the major menaquinone; polar lipids including diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and phosphatidylinositol mannoside; and a DNA G+C content of 73.1 mol%. On the basis of the phenotypic and phylogenetic distinctiveness, the novel isolates are considered to represent members of a novel species of the genus Angustibacter, for which the name Angustibacter speluncae sp. nov. is proposed, with type strain YC2-20T (=KCTC 39842T=DSM 103769T).