Phylogenetic and phenotypic analysis of cultivable marine bacteria isolated from laboratory cultures of two paralytic shellfish toxin-producing dinoflagellates, Gymnodinium catenatum and Alexandrium tamarense, showed the presence of a novel group of Gram-negative, aerobic, moderately halophilic and hydrocarbon-degrading bacteria, related to the genus Marinobacter. The strains, designated DG893T, DG1136 and ATAM407-13, grew optimally in media with 3-6 % NaCl and at 25-30 degrees C, and all could utilize n-hexadecane and n-tetradecane as the sole carbon source. The strains had a 16S rRNA gene sequence similarity of 94.2-94.3 % to Marinobacter hydrocarbonoclasticus ATCC 27132, and a similarity of 97.5-97.8 % to the closest phylogenetically related type strain, Marinobacter flavimaris DSM 16070T. DNA-DNA hybridization levels to M. flavimaris and other Marinobacter type strains were < or = 42 %, while DNA-DNA reassociation values among DG893T, DG1136 and ATAM407-13 were > or = 83 %. The DNA G + C content was 54-55 mol% and the major isoprenoid quinone was ubiquinone-9. On the basis of phenotypic, chemotaxonomic, DNA-DNA hybridization and phylogenetic analysis, it is proposed that these three strains represent a novel species, Marinobacter algicola sp. nov. The type strain is DG893T (= DSM 16394T = NCIMB 14009T).