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

Abstract

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 Rb₁ (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.

Keywords: 16S rRNA gene sequence; Humibacter ginsenosidimutans; bioconversion of ginsenoside; genome sequence; polyphasic taxonomy.