| Abstract |
Strain MF5-112T is a Gram-negative, aerobic, non-motile, ovoid, and non-flagellated bacterium with yellow pigmentation that exhibits oxidase-positive and catalase-negative characteristics. It was isolated from tidal mudflat sediment at a clam farm in Gochang, Republic of Korea. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that strain MF5-112T belongs to the family Flavobacteriaceae. The closest relative was the type strain of Polaribacter huanghezhanensis KCTC 32516T (97.1% 16S rRNA gene sequence similarity), followed by P. pacificus HRA130-1T (96.3%). The major polar lipids were phosphatidylethanolamine, one unidentified phospholipid, two unidentified aminophospholipids, and two unidentified aminolipids. The predominant cellular fatty acids included iso-C15:0, iso-C15:0 3-OH, iso-C17:0 3-OH, anteiso-C15:0, iso-C15:1 G, iso-C13:0, and C15:1ω6c, with menaquinone-6 identified as the major respiratory quinone. The strain MF5-112T exhibits a dual nitrogen metabolism capability, involving both assimilatory nitrate reduction and partial denitrification, which is essential for nitrogen cycling in marine environments. In 72 h, it reduced ammonia nitrogen (NH₄⁺-N) by 59.5% and nitrate nitrogen (NO₃⁻-N) by 42.0%, with ammonia as the preferred nitrogen source. The genome spans 2.6 Mbp with a G + C content of 31.3%, containing 2,454 genes, including 14 related to nitrogen metabolism pathways. Essential genes such as nit-6, nasBDC, nirK, and nirS facilitate the conversion of nitrate and nitrite to ammonia and further reduce nitrite to nitric oxide (NO) and nitrous oxide (N₂O). These characteristics suggest that strain MF5-112T plays a role in nitrogen cycling within sedimentary ecosystems. Based on its unique genetic and phenotypic properties, strain MF5-112T represents a novel species of the genus Polaribacter, for which the name Polaribacter gochangensis sp. nov. is proposed. The type strain is MF5-112T (= KEMB 23950T = KCTC 102318T = JCM 37723T).
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