A Gram-stain-negative, facultatively anaerobic, oxidase-negative and catalase-positive predatory bacillus, designated strain V1718T, was isolated from Xiaoshi Island, PR China. Strain V1718T was found to be closely related to Lujinxingia sediminis SEH01T, with 89.8 % similarity in the 16S rRNA gene sequence, followed by Bradymonas sediminis FA350T with a similarity of 88.4 %. Strain V1718T had the ability to prey on other bacteria, and selective predation on members of Algoriphagus, Nocardioides and Bacillus occurred with the strain. Growth was observed within the range of 20-45 °C (optimal at 37 °C), pH 6.5-9.0 (optimal at pH 8.0) and 1-10 % NaCl (optimal at 3-4 %, w/v). The predominant cellular fatty acids in strain V1718T were iso-C15 : 0 (53.0 %) and C16 : 0 (19.1 %). The major polar lipids present in the strain were phosphatidylglycerol and phosphatidylethanolamine, and the respiratory quinone was menaquinone MK-7. The complete genome sequence of strain V1718T was 5 847 748 bp with a G+C content of 55.2 mol%. The topology of the phylogenomic tree indicated that strain V1718T forms a separate branch in the same clade with the genus Lujinxingia and the family Bradymonadaceae. The average nucleotide identity and average amino acid identity values were 66.4 and 48.6 %, respectively, with Bradymonas sediminis FA350T (type species of Bradymonas) and 66.8 % and 48.9 % with Lujinxingia litoralis B210T (type species of Lujinxingia). The genes related to biosynthesis pathways of several important chemical compounds could not be found in the genome of strain V1718T, which was predicted to be the intrinsic reason for predation in this group. The physiological, biochemical and phylogenetic properties of strain V1718T suggest that it belongs to a novel family distinct from other culturable bradymonabacteria. The name Microvenator marinus gen. nov., sp. nov. is proposed, with strain V1718T (=KCTC 72082T=MCCC 1H00380T) as type strain; the name Microvenatoraceae fam. nov. is also proposed. Meanwhile, the genus Lujinxingia can also be taxonomic classified as Lujinxingiaceae fam. nov. Thus, two novel families and a novel genus of the order Bradymonadales are proposed in this paper.
Keywords: 16S rRNA gene; GTDB; Microvenator; phylogenetic analysis.