Speluncibacterjeojiensis gen. nov. sp. nov., a novel bacterium of the order Mycobacteriales isolated from a cave and a proposal of Speluncibacteraceae fam. nov.

Two Gram- stain- positive, aerobic, non- spore- forming, non- motile, irregular rod- shaped actinobacteria, designated as D2 - 41T and D3- 21, were isolated from soil samples collected in a natural cave in Jeju, Republic of Korea. Both of the isolates were shown to share 100 % 16S rRNA sequence identity. The cell wall contained meso- diaminopimelic acid, arabinose and galactose. The predominant menaquinone was MK- 8(H2). The polar lipids contained phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, an unidentified aminolipid, an unidentified aminoglycolipid, an unidentified phospholipid and two unidentified lipids. The predominant fatty acids were C16:0 and summed feature 3 (C16:1 omega 7c and/or iso-C15: 0 2 - OH). Mycolic acids of C30-C38 were present. The 16S rRNA gene trees showed that the organisms occupied a distinct position remotely located from recognized genera within the order Mycobacteriales, albeit with the 16S rRNA gene similarities of 97.0-97.1 % with Rhodococcus olei, Rhodococcus rhodnii and Rhodococcus triatomae. The genome sizes and DNA G+C contents of strains D2 - 41T and D3- 21 were 4.77-4.88 Mbp and 69.8 mol%, respectively. Both of the isolates shared an average nucleotide identity of 99.4 % and digital DNA-DNA hybridization of 95.2 % to each other, revealing that strains D2 - 41T and D3- 21 belonged to the same species. In the core genome- based phylogenomic tree, both of the isolates were found to be closely associated with members of the genus Tomitella. However, strains D2 - 41T and D3- 21 revealed the highest amino acid identity values (mean 66.5 %, range 66.2-67.0 % with the genus Prescottella of the family Nocardiaceae, followed by the genus Tomitella (mean 64.1 %, range 63.6-64.7 %) of the family Tomitellaceae. Based on the combined data obtained here, the novel isolates belong to a new genus of the new family for which the name Speluncibacter jeojiensis gen. nov. sp. nov. is proposed, with Speluncibacteraceae fam. nov. The type strain is strain D2 - 41T (=KACC 17930T=DSM 101875T).