A novel Gram-negative, non-spore forming, rod-shaped aerobic bacterium, designated SSW136^T, was isolated from a surface seawater sample collected at Espalamaca (in Faial Island), Azores. Growth was found to occur from 10 to 37 °C, pH 6.0–8.0, and with 2-11 % of NaCl. 16S rRNA gene sequence indicated that the strain SSW136^T belongs to the family Rhodobacteraceae. Strain SSW136^T exhibited 96.3, 95.9, 95.7 and 95.5 sequence similarity to the type strains Oceanicola litoreus M-M22^T, Roseovarius aestuarii SMK-122^T, Marivita geojedonensis DPG-138T, and Pseudoruegeria aquimaris SW-255^T respectively. Neighbour-joining and maximum-parsimony phylogenetic trees based on 16S rRNA gene sequences revealed that strain SSW136^T was affiliated to the family Rhodobacteraceae and formed a separate branch. The G+C content was 63.5 mol%. The major respiratory quinone was found to be Q-10. The polar lipids of strain SSW136^T consisted of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminolipids and three unidentified phospholipids. The major fatty acids were C_18:1 Omega7c (46.5 %), Cyclo-CCyclo-C_19:0 Omega 8c (16.0 %) and C16:0 (12.8 %). On the basis of the morphological, genotypic, chemotaxonomic characteristics and low DNA–DNA relatedness, strain SSW136^T is proposed to represent a novel genus and novel species, Nioella nitratireducens gen. nov., sp. nov., in the family Rhodobacteraceae. The type strain is SSW136^T (=KCTC 32417^T = NCIM 5499^T)