Roseobacter algicola sp. nov., a New Marine Bacterium Isolated from the Phycosphere of the Toxin-Producing Dinoflagellate Prorocentrum lima

1 Centre National de la Recherche Scientifique and Université Paris VI, Station Zoologique, F-06230 Villefranche-sur-Mer, France 2 IFREMER, Centre de Nantes, F-44037 Nantes Cedex 01, France 3 Institut National de la Santé et de la Recherche Médicale Unité 303, F-06300 Nice, France * Corresponding author. ABSTRACT We describe a new species on the basis of phenotypic characteristics and the results of an analysis of small-subunit rRNA sequences. Three strains of this organism were isolated from a culture of the toxin-producing dinoflagellate Prorocentrum lima . These bacteria are gram-negative, strictly aerobic, ovoid organisms that are motile by means of one or two subpolar flagella. They grow at temperatures ranging from 10 to 37°C and in the presence of NaCI concentrations ranging from 0.1 to 2 M and have an absolute requirement for sodium ions. They are strictly aerobic with a nonfermentative type of metabolism and are not able to grow anaerobically in presence or absence of nitrate. They do not denitrify. They exhibit oxidase, catalase, gelatinase, esculinase, β-galactosidase, and (to a lesser extent) amylase activities. The three strains which we examined require thiamine and biotin for growth. They grow only when glucose, trehalose, saccharose, fructose, maltose, pyruvate, malate, citrate, esculin, 2-ketoglutarate, 5-ketogluconate, glutamate, or shikimate is present as a sole carbon source. The three strains have identical small-subunit rRNA sequences. A phylogenetic analysis of these sequences revealed that these bacteria belong to the alpha subdivision of the Proteobacteria and that they form a distinct and robust monophyletic group with Roseobacter denitrificans and Roseobacter litoralis . This result and the general phenotypic characteristics of the organisms place them in the genus Roseobacter , although they do not produce bacteriochlorophyll a , in contrast to previously described Roseobacter species. On the basis of the phenotypic and genetic similarities of these strains, we assigned them to a single species, for which the name Roseobacter algicola is proposed. The type strain is R. algicola FF3 (= ATCC 51440).