A taxonomic study was carried out on two isolates, strains BL1(T) and BL11, from marine sediment collected from the East Sea, Korea. Comparative 16S rRNA gene sequence studies showed that these isolates clearly affiliated with the Gammaproteobacteria. BL1T and BL11 were most closely related to Oceanisphaera litoralis KMM 3654T (97.6 and 97.7 % 16S rRNA gene sequence similarity, respectively). The level of 16S rRNA gene sequence similarity between strains BL1T and BL11 was 99.7 %. The two isolates were Gram-negative, aerobic, moderately halophilic, and grew in 0.5-8.0 % NaCl and at 4-42 degrees C. Strains BL1T and BL11 shared some physiological and biochemical properties with O. litoralis KMM 3654T, although they differed in that BL1T and BL11 were able to utilize ethanol, proline and alanine. The G+C contents of the genomic DNA of strains BL1T and BL11 were 56.6 and 57.1 mol%, respectively. Both strains possessed C(16 : 1)omega7c and/or iso-C(15 : 0) 2-OH, C(16 : 0) and C(18 : 1)omega7c as the major fatty acids. DNA-DNA relatedness data indicated that strains BL1T and BL11 represent a genomic species that is separate from O. litoralis KMM 3654T. On the basis of polyphasic evidence, it is proposed that strain BL1T (=KCTC 12522T = DSM 17589T) represents the type strain of a novel species, Oceanisphaera donghaensis sp. nov.