%0 Journal Article %J Science %D 2012 %T Unicellular cyanobacterium symbiotic with a single-celled eukaryotic alga %A Thompson, Anne W %A Foster, Rachel A %A Krupke, Andreas %A Carter, Brandon J %A Musat, Niculina %A Vaulot, Daniel %A Kuypers, Marcel M M %A Zehr, Jonathan P %K 2012 %K MicroB3 %K rcc %K SBR$_\textrmP$hyto$_\textrmD$PO %K sbr?hyto$_\textrmd$ipo %X 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 N2 fixation. %B Science %V 337 %P 1546–1550 %G eng %U http://www.sciencemag.org/content/337/6101/1546.abstract %R 10.1126/science.1222700