TRICHODESMIUM, A GLOBALLY SIGNIFICANT MARINE CYANOBACTERIUM

Planktonic marine cyanobacteria of the genus Trichodesmium occur throu ghout the oligotrophic tropical and subtropical oceans. Their unusual adaptations, from the molecular to the macroscopic level, contribute t o their ecological success and biogeochemical importance. Trichodesmiu m fixes nitrogen gas (N-2) under fully aerobic conditions while photos ynthetically evolving oxygen. its temporal pattern of N-2 fixation res ults from an endogenous daily cycle that confines N-2 fixation to dayl ight hours. Trichodesmium colonies provide a unique pelagic habitat th at supports a complex assemblage of consortial organisms. These coloni es often represent a large fraction of the plant biomass in tropical, oligotrophic waters and contribute substantially to primary production . N-2 fixation by Trichodesmium is likely a major input to the marine and global nitrogen cycle.