Acinetobacter fenheensis sp. nov., isolated from freshwater sediment of the Fenhe River Basin, China: polyphasic characterization and genomic analysis

Background Members of the genus Acinetobacter occur widely in aquatic and sedimentary habitats, yet the taxonomic diversity and genomic features of freshwater sediment-associated lineages remain incompletely characterized. This study aimed to determine the taxonomic position of strain FR7-9ᵀ, isolated from sediment of the Fenhe River Basin, China, and to examine genomic traits potentially associated with environmental persistence. Results Strain FR7-9ᵀ was a Gram-stain-negative, facultatively anaerobic, non-motile, short-rod-shaped bacterium that grew at 10–40 °C, pH 5.0–9.5, and 0–8.0% (w/v) NaCl. A genus-wide genome-based phylogenetic analysis using single-copy orthologous proteins placed strain FR7-9ᵀ within the genus Acinetobacter as an independent lineage related to Acinetobacter zhairuonensis, Acinetobacter kanungonis , and Acinetobacter tibetensis . The draft genome comprised 40 contigs totaling 3,332,809 bp and had a DNA G + C content of 42.1%. Average nucleotide identity and digital DNA–DNA hybridization values between FR7-9ᵀ and selected reference type strains were 75.0–84.0% and 20.6–26.7%, respectively, well below accepted species boundaries. The major fatty acids were C 16:0 , C 18:1 ω9c, and summed feature 3; the major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol; and the respiratory quinones were Q-8 and Q-9. Genome analysis identified genes associated with phosphate acquisition and polyphosphate metabolism, together with multiple putative antimicrobial-resistance determinants dominated by efflux-associated genes. Several resistance-associated loci occurred near genes annotated as transposase-, recombination-, plasmid-, or phage-associated. Conclusions Phenotypic, chemotaxonomic, phylogenomic, and genome-relatedness evidence supports recognition of strain FR7-9ᵀ as a novel species of Acinetobacter , for which the name Acinetobacter fenheensis sp. nov. is proposed. The type strain is FR7-9ᵀ (= CICC 25278ᵀ = MCCC 1K08999ᵀ = KCTC 8398ᵀ). Its genome provides a taxonomic and functional baseline for further investigation of nutrient-acquisition and resistance-associated traits in freshwater sediment Acinetobacter .