Syracuse

Unicellular Cyanobacterium Symbiotic with a Single-Celled Eukaryotic Alga

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

Edité par CCSD ; American Association for the Advancement of Science (AAAS) -

International audience. Symbioses between nitrogen (N)(2)-fixing prokaryotes and photosynthetic eukaryotes are important for nitrogen acquisition in N-limited environments. Recently, a widely distributed planktonic uncultured nitrogen-fixing cyanobacterium (UCYN-A) was found to have unprecedented genome reduction, including the lack of oxygen-evolving photosystem II and the tricarboxylic acid cycle, which suggested partnership in a symbiosis. We showed that UCYN-A has a symbiotic association with a unicellular prymnesiophyte, closely related to calcifying taxa present in the fossil record. The partnership is mutualistic, because the prymnesiophyte receives fixed N in exchange for transferring fixed carbon to UCYN-A. This unusual partnership between a cyanobacterium and a unicellular alga is a model for symbiosis and is analogous to plastid and organismal evolution, and if calcifying, may have important implications for past and present oceanic N-2 fixation.

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