Oceanicaulis alexandrii gen. nov., sp. nov., a novel stalked bacterium isolated from a culture of the dinoflagellate Alexandrium tamarense (Lebour) Balech Carsten Stro ¨ mpl, 1 Georgina L. Hold, 2 3 Heinrich Lu ¨ nsdorf, 1 Jennifer Graham, 2 Susan Gallacher, 2 Wolf-Rainer Abraham, 1 Edward R. B. Moore 1 4 and Kenneth N. Timmis 1 Correspondence Carsten Stro ¨ mpl cst@gbf.de 1 Division of Microbiology, German Research Centre for Biotechnology (GBF), Mascheroder Weg 1, 38124 Braunschweig, Germany 2 Fisheries Research Services, Marine Laboratory, Victoria Road, Aberdeen AB11 9DB, UK Five bacterial strains were isolated from a non-toxigenic strain of the marine dinoflagellate Alexandrium tamarense (Lebour) Balech CCMP 116 (NEPCC C116), during a survey of the diversity of bacteria associated with paralytic shellfish toxin-producing cultures of Alexandrium spp. (Dinophyta). All strains were strictly aerobic, Gram-negative, straight or curved rods. Cells were dimorphic, with stalks (or prosthecae) and non-motile or non-stalked and motile, by means of a single polar flagellum. The bacteria grew best at salt concentrations ranging from 2 to 10 % and growth occurred at 10 6C, but not at 50 6C. The G+C content of the chromosomal DNA of the strains was determined to be 61–62 mol%. Major cellular fatty acids of the bacteria presented a unique profile. 16S rRNA gene sequence analysis showed the five strains to be related to genera of budding bacteria of marine origin in the ‘Alphaproteobacteria’, namely, Hirschia, Maricaulis and Hyphomonas, although they exhibited substantial differences in morphology, substrate utilization and fatty acid profile to members of these genera. The five strains are proposed to comprise a new species of a new genus, Oceanicaulis alexandrii gen. nov., sp. nov., the type strain of which is C116-18 T (=DSM 11625 T =NCIMB 13905 T ). Since the original description of the genus Caulobacter by Henrici & Johnson (1935), stalked bacteria from a wide range of sources, including soils, freshwater and marine environments, have been assigned to the genus, mainly on the basis of their characteristic prosthecate (Anast & Smit, 1988; Stahl et al., 1992). Originally thought to be restricted exclusively to oligotrophic habitats, in the last decade an extensive number of isolates exhibiting heterotrophic traits and relatively versatile metabolisms have been isolated from eutrophic environments, such as secondary waste water treatment facilities (Fenton, 1994; MacRae & Smit, 1991), and assigned to the genus Caulobacter. It sub- sequently became clear, from 16S rRNA gene sequence analyses, that these isolates and the previously described species of Caulobacter were genotypically heterogeneous (Stahl et al., 1992), and other studies (Ariskina, 1995; Moore, 1978; Nikitin et al., 1990) supported these findings. A polyphasic analysis (Abraham et al., 1999) of the validly published Caulobacter species, members of the phylogeneti- cally related genus Brevundimonas and other unpublished caulobacterial isolates yielded a reclassification of many of the described species of Caulobacter and the proposal of a new genus, Maricaulis, to accommodate the strictly halophilic species. Caulobacter sensu stricto is currently composed of only freshwater species and isolates with a specific range of 16S rRNA gene sequence similarity, a characteristic membrane protein antigen and typical polar lipid fingerprints. The amended genus Brevundimonas (Abraham et al., 1999), as defined by the same methods, 3Present address: Department of Medicine and Therapeutics, Univer- sity of Aberdeen, Polwarth Building, Foresterhill, Aberdeen AB25 2ZD, UK. 4Present address: The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK. Published online ahead of print on 20 June 2003 as DOI 10.1099/ ijs.0.02635-0. The EMBL accession numbers for the 16S rRNA gene sequences of Oceanicaulis alexandrii C116-3 and C116-18 T are AJ309863 and AJ309862, respectively. A selection of 16S rDNA sequence stretches and helices where the five strains of O. alexandrii exhibit diagnostic differences from related genera (Table I) and characteristics useful for differentiating the genus Oceanicaulis from related genera (Table II) are available in IJSEM Online. 02635 G 2003 IUMS Printed in Great Britain 1901 International Journal of Systematic and Evolutionary Microbiology (2003), 53, 1901–1906 DOI 10.1099/ijs.0.02635-0