Letter

Nature 439, 847-850 (16 February 2006) | doi:10.1038/nature04435

Proteorhodopsin lateral gene transfer between marine planktonic Bacteria and Archaea

Niels-Ulrik Frigaard1,2, Asuncion Martinez1, Tracy J. Mincer1 and Edward F. DeLong1

Planktonic Bacteria, Archaea and Eukarya reside and compete in the ocean's photic zone under the pervasive influence of light. Bacteria in this environment were recently shown to contain photoproteins called proteorhodopsins, thought to contribute to cellular energy metabolism by catalysing light-driven proton translocation across the cell membrane1, 2, 3, 4, 5, 6, 7. So far, proteorhodopsin genes have been well documented only in proteobacteria and a few other bacterial groups. Here we report the presence and distribution of proteorhodopsin genes in Archaea affiliated with the order Thermoplasmatales, in the ocean's upper water column. The genomic context and phylogenetic relationships of the archaeal and proteobacterial proteorhodopsins indicate its probable lateral transfer between planktonic Bacteria and Archaea. About 10% of the euryarchaeotes in the photic zone contained the proteorhodopsin gene adjacent to their small-subunit ribosomal RNA. The archaeal proteorhodopsins were also found in other genomic regions, in the same or in different microbial lineages. Although euryarchaeotes were distributed throughout the water column, their proteorhodopsins were found only in the photic zone. The cosmopolitan phylogenetic distribution of proteorhodopsins reflects their significant light-dependent fitness contributions, which drive the photoprotein's lateral acquisition and retention, but constrain its dispersal to the photic zone.

  1. Department of Civil and Environmental Engineering and Division of Biological Engineering, Massachusetts Institute of Technology, Building 48, 15 Vassar Street, Cambridge, Massachusetts 02139, USA
  2. †Present address: Institute of Molecular Biology and Physiology, University of Copenhagen, Sølvgade 83H, 1307 Copenhagen K, Denmark

Correspondence to: Edward F. DeLong1 Correspondence and requests for materials should be addressed to E.F.D. (Email: delong@mit.edu). The sequences reported here have been deposited in GenBank under accession numbers DQ257435, DQ257434, DQ156349, DQ156348 (fosmids HF10_3D09, HF70_19B12, HF70_39H11 and HF70_59C08), DQ156379–DQ156483 (SSU rRNA), DQ156350–DQ156363, DU708536–DU708556 (fosmid termini) and DQ156364–DQ156378 (proteorhodopsin sequences).

Received 8 August 2005; Accepted 15 November 2005

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