Aquimarina rhodophyticola sp. nov. and Aquimarina besae sp. nov., Isolated from Marine Red Algae.

Abstract

Two Gram-negative, oxidase- and catalase-positive, non-motile, rod-shaped aerobic bacteria, designated strains W85ᵀ and SS2-1ᵀ, were isolated from marine red algae. Strain W85ᵀ grew optimally at 30 °C, pH 7.0, and 4.0% (w/v) NaCl, while strain SS2-1ᵀ grew optimally at 25-30 °C, pH 7.0, and 2.0-3.0% NaCl. Both strains contained menaquinone-6 as the sole respiratory quinone and shared major fatty acids, including iso-C_15:0, summed feature 9 (C_16:0 10-methyl and/or iso-C_17:1 ω9c), and iso-C_15:1 G, with iso-C_15:0 3-OH additionally present in strain W85ᵀ. The major polar lipids were phosphatidylethanolamine and diphosphatidylglycerol. The complete genomes of strains W85ᵀ (3.67 Mb, 3,151 genes) and SS2-1ᵀ (5.14 Mb, 4,564 genes) had a DNA G + C content of 34.1%. Genome annotation revealed that strain SS2-1ᵀ harbored more carbohydrate-active enzymes (129 genes) than W85ᵀ (60 genes), suggesting enhanced polysaccharide-degrading capacity. Ecological distribution analysis indicated that strains W85ᵀ and SS2-1ᵀ occupy distinct ecological niches, implying potential functional specialization. Both strains shared 95.0% 16S rRNA gene similarity, 71.9% average nucleotide identity (ANI), and 18.5% digital DNA-DNA hybridization (dDDH), all below species-level thresholds. Phylogenetic analyses based on 16S rRNA gene and whole-genome sequences confirmed that strains W85ᵀ and SS2-1ᵀ form distinct lineages within the genus Aquimarina. Furthermore, ANI and dDDH values between each strain and other type strains were also well below the species delineation thresholds. Based on phenotypic, chemotaxonomic, genomic, and ecological characteristics, strains W85ᵀ and SS2-1ᵀ are proposed as Aquimarina rhodophyticola sp. nov. (W85ᵀ = KACC 23858ᵀ = DSM 119937ᵀ) and Aquimarina besae sp. nov. (SS2-1ᵀ = KACC 23859ᵀ = DSM 119931ᵀ), respectively.