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 LZ166(T), was isolated from the bathypelagic seawater in the western Pacific Ocean. The cells were short rod-shaped, oxidase- and catalase-positive, and motile by means of lateral flagella. The growth of strain LZ166(T) was observed at 10-45 °C (optimum 34-37 °C), at pH 5-10 (optimum 6-8), and in the presence of 0-5% NaCl (optimum 1-3%). A phylogenetic analysis based on the 16S rRNA gene showed that strain LZ166(T) shared the highest similarity (98.58%) with Aquibium oceanicum B7(T) and formed a distinct branch within the Aquibium genus. The 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 LZ166(T) and other species within the Aquibium genus, further substantiated its novelty. The genome of strain LZ166(T) was 6,119,659 bp in size with a 64.7 mol% DNA G+C content. The predominant fatty acid was summed feature 8 (C(18:1)ω7c and/or C(18:1)ω6c). 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. The 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 the polyphasic taxonomic results, strain LZ166(T) represented a novel species of the genus Aquibium, for which the name Aquibium pacificus sp. nov. is proposed, with the type strain LZ166(T) (=MCCC M28807(T) = KACC 23148(T) = KCTC 82889(T)).