Humibacter ginsenosidimutans sp. nov., with ginsenoside-converting activity isolated from activated sludge

A novel Gram-stain-positive, thin rod-shaped, non-motile, aerobic and creamy-white pigmented bacterium (designated strain WJ7-1 T ) was isolated from activated sludge sampled in Suwon, Republic of Korea. 16S rRNA gene sequence analysis indicated that the isolate belongs to the genus Humibacter , family Microbacteriaceae , with a sequence similarity of 97.9 % to its nearest neighbour Humibacter albus KACC 20986 T . Strain WJ7-1 T contained menaquinone (MK)-10 (16.0 %), 11 (48.5 %) and 12 (35.5 %) as major respiratory quinones. The predominant cellular fatty acids (>15 %) were anteiso-C 17 : 0 , iso-C 16 : 0 and anteiso-C 15 : 0 . The peptidoglycan of strain WJ7-1 T contained the diagnostic diamino acid ornithine and 2,4-diaminobutyric acid alanine. Alanine, glutamic acid and glycine were also present in the cell wall. The characteristic whole-cell sugars present were glucose, galactose, xylose and rhamnose. The polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol, an unidentified glycolipid and two unidentified phospholipids. Strain WJ7-1 T possessed ginsenoside-converting ( β -glucosidase) activity, which enabled it to transform ginsenoside protopanaxadiol-type Rb 1 (one of the dominant active components of ginseng) to compound K. The genome size of strain WJ7-1 T has 4.2 Mbp and the G+C content is 68.3 mol%. Average nucleotide identity, amino acid identity and digital DNA–DNA hybridization values between strain WJ7-1 T and the closely related strain were 79.8, 36.1 and 23.5 %, respectively, indicating that strain WJ7-1 T represents a novel species of the genus Humibacter . Strain WJ7-1 T could be distinguished from the other members of the genus Humibacter by a number of chemotaxonomic and phenotypic characteristics. Based on polyphasic taxonomic analysis, strain WJ7-1 T (=KACC 19729 T =LMG 30802 T ) represents a novel species within the genus Humibacter , for which the name Humibacter ginsenosidimutans sp. nov. is proposed.