A novel Gram-stain-negative, aerobic, rod-shaped and non-motile bacterium, designated strain 25HG05S-68ᵀ, was isolated from freshwater of the Seomgang River, Republic of Korea. Phylogenetic analysis based on the 16S rRNA gene sequence placed the strain within the family Comamonadaceae, showing ≤97.2% similarity to type strains of validly published species, indicating that it represents a novel genus and species. The complete genome comprises a single circular chromosome of 6.12 Mb with a G+C content of 61.5 mol%. Average nucleotide identity (73.4-75.0%), average amino acid identity (68.9-71.0%), digital DNA-DNA hybridization (19.6-20.4%) and percentage of conserved proteins (44.7-58.2%) values between strain 25HG05S-68ᵀ and its closest relatives were well below the accepted thresholds for both species and genus delineation. Phylogenomic analyses using both the Type (Strain) Genome Server and the up-to-date bacterial core gene pipeline confirmed that the strain formed a separate and well-supported clade distinct from all described genera within the family. The genome encoded a full complement of genes for the Embden-Meyerhof-Parnas pathway, gluconeogenesis, the tricarboxylic acid cycle and assimilatory sulphate reduction. Phenotypically, the strain grew at 20-35 °C (optimum, 25 °C), pH 4.0-9.0 (optimum, pH 7.0) and tolerated up to 1.0% (w/v) NaCl. It exhibited positive catalase and oxidase activities and showed hydrolytic activity towards chitin, hypoxanthine and l-tyrosine. The major cellular fatty acids of strain 25HG05S-68ᵀ were summed feature 3 (C16:1 ω6c and/or C16:1 ω7c), C10:0 3-OH and C15:1 ω6c. The predominant respiratory quinone was ubiquinone-8, and the polar lipid profile included diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. Comprehensive evidence from phylogenetic, genomic, phenotypic and chemotaxonomic analyses supports the classification of strain 25HG05S-68ᵀ as a novel genus and species within the family Comamonadaceae, for which the name Hydrophilobacter chitinilyticus gen. nov., sp. nov. is proposed. The type strain is 25HG05S-68ᵀ (=FBCC-B19484ᵀ =MCCC 1K10059ᵀ).
Choi et al. (Mon,) studied this question.