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Unicellular Cyanobacterium Symbiotic with a Single-Celled Eukaryotic Alga

2012; American Association for the Advancement of Science; Volume: 337; Issue: 6101 Linguagem: Inglês

10.1126/science.1222700

1095-9203

Anne Thompson, Rachel A. Foster, Andreas Krupke, Brandon J. Carter, Niculina Musat, Daniel Vaulot, Marcel M. M. Kuypers, Jonathan P. Zehr,

Marine and coastal ecosystems

Fixing on a Marine Partnership Nitrogen fixation by microorganisms determines the productivity of the biosphere. Although plants photosynthesize by virtue of the ancient incorporation of cyanobacteria to form chloroplasts, no equivalent endosymbiotic event has occurred for nitrogen fixation. Nevertheless, in terrestrial environments, nitrogen-fixing symbioses between bacteria and plants, for example, are common. Thompson et al. (p. 1546 ) noticed that the ubiquitous marine cyanobacterium UCYN-A has an unusually streamlined genome lacking components of the photosynthetic machinery and central carbon metabolism—all suggestive of being an obligate symbiont. By using gentle filtration methods for raw seawater, a tiny eukaryote partner for UCYN-A of less than 3-µm in diameter was discovered. The bacterium sits on the cell wall of this calcifying picoeukaryote, donating fixed nitrogen and receiving fixed carbon in return.