A recently discovered symbiosis in the ocean

Fixed nitrogen is an essential requirement for the biosynthesis of cellular nitrogenous compounds. Some cyanobacteria can fix nitrogen, contributing significantly to the nitrogen cycle, agriculture and biogeochemical history of Earth. The marine N₂-fixing cyanobacteria in the open ocean are diverse and include free-living cyanobacteria, several symbionts and the symbiotic unicellular (UCYN-A) which have been recently discovered. UCYN-A exhibits dramatic genomic reductions. The genome reduction implies that the cyanobacterium must have an obligate symbiosis with the host. Moreover, incubation of seawater with labeled nutrients demonstrated nitrogen transfer from the cyanobacterium to the host, and carbon transfer from host to cyanobacterium. Many similar symbioses probably exist in the environment but are difficult to detect or study because they are small, not easily visualized or characterized, and difficult to manipulate experimentally.

Speaker: Dr. Maria del Carmen Munoz-Marin, UC Santa Cruz