Nitrogen fixation-the reduction of dinitrogen (N2) gas to biologically available nitrogen (N)-is an important source of N for terrestrial and aquatic ecosystems. In terrestrial environments, N2-fixing symbioses involve multicellular plants, but in the marine environment these symbioses occur with unicellular planktonic algae. An unusual symbiosis between an uncultivated unicellular cyanobacterium (UCYN-A) and a haptophyte picoplankton alga was recently discovered in oligotrophic oceans. UCYN-A has a highly reduced genome, and exchanges fixed N for fixed carbon with its host. This symbiosis bears some resemblance to symbioses found in freshwater ecosystems. UCYN-A shares many core genes with the 'spheroid bodies' of Epithemia turgida and the endosymbionts of the amoeba Paulinella chromatophora. UCYN-A is widely distributed, and has diversified into a number of sublineages that could be ecotypes. Many questions remain regarding the physical and genetic mechanisms of the association, but UCYN-A is an intriguing model for contemplating the evolution of N2-fixing organelles.
CITATION STYLE
Zehr, J. P., Shilova, I. N., Farnelid, H. M., Muñoz-Maríncarmen, M. D. C., & Turk-Kubo, K. A. (2016, December 20). Unusual marine unicellular symbiosis with the nitrogen-fixing cyanobacterium UCYN-A. Nature Microbiology. Nature Publishing Group. https://doi.org/10.1038/nmicrobiol.2016.214
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