Unicellular Cyanobacterium Symbiotic with a Single-Celled Eukaryotic Alga
Creators
- 1. Ocean Sciences, University of California, Santa Cruz, CA 95064, USA.
- 2. Max-Planck-Institut für Marine Mikrobiologie, Bremen, Germany D-28359.
- 3. UPMC (Paris-06) and CNRS, UMR 7144, Station Biologique, Place G. Tessier 29680 Roscoff, France.
Description
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.