1. Department of Marine Sciences, University of Georgia, Athens, Georgia 30602, USA
2. Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA
3. Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
4. Departmento de Microbiologia y Biologia Celular, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
5. The Institute for Genomic Research, 9712 Medical Center Drive, Rockville, Maryland 20850, USA
6. Department of Marine Sciences, University of South Alabama, Mobile, Alabama 36688, USA and Dauphin Island Sea Lab, Dauphin Island, Alabama 36528, USA
7. Department of Biochemistry, Microbiology and Molecular Biology, Darling Marine Center, University of Maine, Walpole, Maine 04573, USA
8. Center of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 East Pratt Street Baltimore, Maryland 21202, USA
9. Department of Biology, 1001 E. 3rd Street, Jordan Hall 418, Indiana University, Bloomington, Indiana 47405, USA
10. Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205, USA

Correspondence to: Mary Ann Moran¹ Email: mmoran@uga.edu
The complete sequence has been submitted to the GenBank database under accession numbers s_pomeroyi_dss_3_267 CP000031 and s_pomeroyi_dss_3_267 CP000032.

Abstract

Since the recognition of prokaryotes as essential components of the oceanic food web¹, bacterioplankton have been acknowledged as catalysts of most major biogeochemical processes in the sea. Studying heterotrophic bacterioplankton has been challenging, however, as most major clades have never been cultured² or have only been grown to low densities in sea water^{3, 4}. Here we describe the genome sequence of Silicibacter pomeroyi, a member of the marine Roseobacter clade (Fig. 1), the relatives of which comprise 10–20% of coastal and oceanic mixed-layer bacterioplankton^{2, 5, 6, 7}. This first genome sequence from any major heterotrophic clade consists of a chromosome (4,109,442 base pairs) and megaplasmid (491,611 base pairs). Genome analysis indicates that this organism relies upon a lithoheterotrophic strategy that uses inorganic compounds (carbon monoxide and sulphide) to supplement heterotrophy. Silicibacter pomeroyi also has genes advantageous for associations with plankton and suspended particles, including genes for uptake of algal-derived compounds, use of metabolites from reducing microzones, rapid growth and cell-density-dependent regulation. This bacterium has a physiology distinct from that of marine oligotrophs, adding a new strategy to the recognized repertoire for coping with a nutrient-poor ocean.

Figure 1: Phylogenetic tree of 16S rRNA gene sequences from the Roseobacter clade and other major marine taxa.

Sequences include those from uncultured bacterioplankton (open square) and from cultured bacterioplankton isolated at very low nutrient concentrations (filled circle). Scale bar shows Jukes–Cantor evolutionary distance.

High resolution image and legend (40K)

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