A Gram-stain-negative, tyrosine-metabolizing, non-motile, strictly aerobic, non-spore-forming, rod-shaped marine bacterium, designated strain CC-PW-75, was isolated from the estuarine water off Pintung, Taiwan. Strain CC-PW-75 formed a distinct phyletic lineage associated with Gemmobacter species, sharing the highest 16S rRNA gene sequence similarity with G. megaterium CF17 and G. straminiformis CAM-8 (96.0% each) followed by G. aquatilis IFAM 1031 and G. nectariphilus AST4 (95.8% each). Analysis of the draft genome (3.76 Mbp) revealed the presence of genes encoding light-harvesting complexes, photosynthetic reaction centers and proteins involved in the metabolism of CO, CO, HCO and HS. However, bacteriochlorophyll a was not detected. Average nucleotide identity values between the genome sequence of CC-PW-75 and the related Gemmobacter species (n = 6) were estimated to be 72.8-76.3%. Polar lipid analysis revealed the presence of phosphatidylglycerol, phosphatidylethanolamine and an unidentified lipid in major amounts, and phosphatidylmonomethylethanolamine, phosphatidylcholine, an unidentified aminolipid and an unidentified lipid in minor amounts. Cω7c and/or Cω6c, C and Cω7c 11-methyl were identified to be major fatty acids. The DNA G + C content was 66.2 mol% (draft genome sequence). Ubiquinone-10 (Q-10) was the sole respiratory quinone. Based on the polyphasic taxonomic evidence, CC-PW-75 is most likely a novel species of the genus Gemmobacter, affiliated to the family Rhodobacteraceae, for which the name Gemmobacter aestuarii sp. nov. is proposed. The type strain is CC-PW-75 (= JCM 19754 = BCRC 80759). Also, we propose the reclassification of Cereibacter changlensis as Gemmobacter changlensis Chen et al. 2013 using the polyphasic data presented in this study.