A Gram-negative, non-spore-forming, catalase- and oxidase-positive, strictly aerobic, short rod-shaped bacterium with a single, polar flagellum, designated strain WH169(T), was isolated from seawater of the Yellow Sea in China. Buds and prosthecae were formed when the organism was grown at 20 degrees C for 12 days on marine 2216E agar. The organism grew optimally at 37 degrees C, in pH 7.0-8.0, and in the presence of 4.0-6.0% w/v NaCl. Growth did not occur in a medium without Na(+) or sea salts. Strain WH169(T) contained ubiquinone-8 as the predominant respiratory lipoquinone and C(16:1)omega7c and/or C(16:1)omega6c (35.9%), C(16:0) (25.3%) and C(18:1)omega7c (9.7%) as the major fatty acids. The polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol and an unidentified phospholipid. The DNA G+C content of strain WH169(T) was 49.4 mol%. 16S rRNA gene sequence analysis showed that strain WH169(T) showed 95.1% sequence similarity to both type strains of the only two species in the genus Aestuariibacter. On the basis of the polyphasic taxonomic evidence presented in this study, it was concluded that strain WH169(T) should be classified as a novel species of Aestuariibacter, for which the name Aestuariibacter aggregatus sp. nov. is proposed, with the type strain WH169(T) (=CGMCC 1.8995(T)=LMG 25283(T)).