Trichodesmium is a genus of filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters (particularly around Australia, where they were first described by Captain Cook). Trichodesmium fixes atmospheric nitrogen into a form usable to living things. While far from the only nitrogen fixing bacteria, they are among the most important of the marine varieties, and are being extensively studied for their role in nutrient cycling in the ocean. Unlike other nitrogen fixing bacteria, Trichodesmium does not have heterocysts. Instead, atmospheric nitrogen is processed in special, protective cells called diazocytes. Nitrogen fixation peaks at mid-day, during which photosynthesis is put on hold, in order to protect the enzyme nitrogenase from oxygen. The same nitrogen-fixing strategy has also been identified in Katagnymene, another marine cyanobacteria.
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