Albibacterium profundi sp. nov., isolated from sediment of the Challenger Deep of Mariana Trench, and reclassification of Pedobacter indicus as Albibacterium indicum comb. nov.

A rod-shaped, white-pigmented, non-motile, Gram-stain-negative bacterium, designated RHL897^T, was isolated from sediments collected at the Mariana Trench Challenger Deep (10,816 m). Strain RHL897^T was strictly aerobic and grew at 4-37 °C, pH 6.0-10.0 and in the presence of 0-11.0 % (w/v) NaCl. Its genomic DNA G+C content was 41.2%. Metabolic analysis revealed mechanisms for salt tolerance, abundant metal ion transport proteins and stronger resistance to heavy metals such as arsenic and mercury compared to the closest reference strains, likely linked to adaptation to the hadal sediment environment. The predominant menaquinone was MK-7, and the major polar lipids were phosphatidylethanolamine, an unidentified aminophospholipid and an unidentified glycolipid. The main fatty acids were iso-C_{15 : 0}, summed feature 3 (C_{16 : 1} <i>ω7c</i> and/or C_{16 : 1} <i>ω6c</i>) and iso-C_{17 : 0} 3OH. Strain RHL897^T exhibited the highest 16S rRNA gene sequence similarity to the type strain of <i>Pedobacter indicus</i> (97.9%) and <i>Albibacterium bauzanense</i> (96.1%). Phylogenetic trees constructed based on 16S rRNA gene sequences and a 549 core gene set indicated that strain RHL897^T was closely related to <i>P. indicus</i> and <i>A. bauzanense</i>, with all three species clustering within a distinct clade. Combined with the analyses of average nucleotide identity, average amino acid identity and digital DNA-DNA hybridization, strain RHL897^T represented a novel species of the genus <i>Albibacterium</i>, for which the name <i>Albibacterium profundi</i> sp. nov. is proposed. The type strain is RHL897^T (=MCCC 1K09221^T=KCTC 102276^T). Furthermore, the revised phylogeny with the inclusion of RHL897^T suggested that <i>P. indicus</i> should be reclassified under the genus <i>Albibacterium</i> and renamed <i>Albibacterium indicum</i>.