Aquibium pacificus sp. nov., a Novel Mixotrophic Bacterium from Bathypelagic Seawater in the Western Pacific Ocean

A novel Gram-stain-negative, facultatively anaerobic and mixotrophic bacterium, designated as strain LZ166T, was isolated from the bathyplagic seawater in the western Pacific Ocean. Cells were short rod-shaped, oxidase- and catalase- positive, and motile by means of lateral flagella. Growth of strain LZ166T was observed at 10-45 ℃ (optimum, 34-37 ℃), at pH 5-10 (optimum, 6-8) and in the presence of 0-5% NaCl (optimum, 1-3%). Phylogenetic analysis based on the 16S rRNA gene showed that strain LZ166T shared the highest similarity (98.58%) with Aquibium oceanicum B7T, and formed a distinct branch within the Aquibium genus. Genomic characterization, including average nucleotide identity (ANI, 90.73-76.79%), average amino identity (AAI, 88.50-79.03%) and digital DNA-DNA hybridization (dDDH, 36.1-22.2%) values between LZ166T and other species within the Aquibium genus, further substantiated its novelty. The genome of strain LZ166T was 6,119,659 bp in size with a 64.7 mol% DNA G+C content. The predominant fatty acid was summed feature 8 (C18:1ω7c and/or C18:1ω6c). The major polar lipids identified were Diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), glycolipid (GL) and phosphatidylglycerol (PG), with ubiquinone-10 (Q-10) as the predominant respiratory quinone. Genomic annotation indicated the presence of genes for a diverse metabolic profile, including pathways for carbon fixation via the Calvin–Benson–Bassham cycle and inorganic sulfur oxidation. Based on polyphasic taxonomic results, strain LZ166T represented a novel species of the genus Aquibium, for which the name Aquibium pacificus sp. nov., is proposed, with the type strain LZ166T (= MCCC M28807T = KACC 23148T = KCTC 82889T).