A novel strain KS-M25(T)was isolated from estuary water in South Korea. Strain KS-M25(T)was Gram-staining-negative, strictly aerobic, motile rods-shaped bacterium and showed oxidase- and catalase-positive reactions. Growth of strain KS-M25(T)was observed at 10-25 degrees C (optimum, 20 degrees C), at pH 5.5-9.0 (optimum, pH 7.5), and with 0-6.0% (w/v) NaCl (optimum, 1%). Ubiquinone-8 was identified as the sole isoprenoid quinone and the major fatty acids were C(16:0,)cyclo-C(17:0)and sum in feature 3 (comprising C-16:1 omega 7c and/or C-16:1 omega 6c). The G+C content values based on genome sequences was 62.3 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain KS-M25(T)formed a clear cluster within the genusAchromobacter. Strain KS-M25(T)was most closely related toAchromobacter anxiferLMG 26857(T),Achromobacter dolensLMG 26840(T), andAchromobacter xylosoxidansNBRC 15126(T)with 97.8%, 97.8%, and 97.7% 16S rRNA gene sequence similarities, respectively. Based on phenotypic, chemotaxonomic, and phylogenetic analysis, strain KS-M25(T)represents a novel species of the genesAchromobacter, for which the nameAchromobacter aestuariisp. nov. is proposed. The type strain is KS-M25(T)(= KACC 21219(T) = JCM 33329(T)).