Phreatobacter stygius sp. nov., isolated from pieces of wood in a lava cave and emended description of the genus Phreatobacter.

An aerobic, Gram-negative, catalase-positive, oxidase-positive bacterium, designated strain YC6-17T, was isolated from pieces of wood collected at the bottom of Youngcheon Cave in Jeju, Republic of Korea. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain YC6-17T formed a tight cluster with Phreatobacter oligotrophus DSM 25521T (98.1 % sequence similarity) and was distinctly separate from other taxa of the order Rhizobiales. Cells were motile rods and showed growth at 10-30 °C, pH 6-8 and 2 % NaCl. Colonies were smooth, circular, convex and pale yellow in colour. The predominant ubiquinone was Q-10. The predominant fatty acids were C18 : 1ω7c, 11-methyl-C18 : 1ω7c, summed feature 3 and C16 : 0. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, two glycolipids and a lipid. The DNA G+C content was 64.4 mol%. DNA-DNA relatedness between strain YC6-17T and the closest relative was 15.6±7.9 %. Based on combined data from phenotypic characterization and DNA-DNA hybridization as well as phylogenetic analysis, it was suggested that the isolate represents a novel species of the genus Phreatobacter, for which the name Phreatobacter stygius sp. nov. is proposed. The type strain is strain YC6-17T (=KCTC 52518T=DSM 103734T).