A polyphasic taxonomic approach was used to characterize two novel bacterial strains, HDW17AT and HDW17BT, isolated from the intestine of the diving beetle Cybister lewisianus, and the dark diving beetle Hydrophilus acuminatus, respectively. Both strains were Gram-positive and facultative anaerobic cocci forming cream-colored colonies. The isolates grew optimally at 25°C, pH 7, in the presence of 0.3% (wt/vol) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences and genome sequences showed that the isolates were members of the genus Vagococcus, and strain HDW17AT was closely related to Vagococcus fessus CCUG 41755T (98.9% of 16S rRNA gene sequence similarity and 74.3% of average nucleotide identity [ANI]), whereas strain HDW17BT was closely related to Vagococcus fluvialis NCFB 2497T (98.9% of 16S rRNA gene sequence similarity and 76.6% of ANI). Both strains contained C16:0, and C18:1ω9c as the major cellular fatty acids, but C16:1ω9c was also observed only in strain HDW17BT as the major cellular fatty acid. The respiratory quinone of the isolates was MK-7. The major polar lipid components were phosphatidylglycerol, phosphatidylethanolamine, and diphosphatidylglycerol. The genomic DNA G + C content of strains HDW17AT and HDW17BT were 36.6 and 34.4%, respectively. Both strains had cell wall peptidoglycan composed of the amino acids L-alanine, glycine, D-glutamic acid, L-tryptophan, L-lysine, and L-aspartic acid, and the sugars ribose, glucose, and galactose. Based on phylogenetic, phenotypic, chemotaxonomic, and genotypic analyses, strains HDW17AT and HDW17BT represent two novel species in the genus Vagococcus. We propose the name Vagococcus coleopterorum sp. nov. for strain HDW17AT (= KACC 21348T = KCTC 49324T = JCM 33674T) and the name Vagococcus hydrophili sp. nov. for strain HDW17BT (= KACC 21349T = KCTC 49325T = JCM 33675T).
Keywords: Cybister lewisianus; Hydrophilus acuminatus; Vagococcus; Vagococcus coleopterorum; Vagococcus hydrophili; diving beetle.