Trichodesmium 720415 217311796 2008-06-05T14:13:02Z Dumelow 805775 fix link to dab page {{Taxobox | color = lightgrey | name = ''Trichodesmium'' | regnum = [[Bacterium|Bacteria]] | divisio = [[Cyanobacteria]] | ordo = [[Oscillatoriales]] | genus = '''''Trichodesmium''''' | subdivision_ranks = Species | subdivision = ''[[Trichodesmium contortum|T. contortum]]''<br/> ''[[Trichodesmium erythraeum|T. erythraeum]]''<br/> ''[[Trichodesmium hildebrandtii|T. hildebrandtii]]''<br/> ''[[Trichodesmium tenue|T. tenue]]''<br/> ''[[Trichodesmium thiebautii|T. thiebautii]]'' }} <!-- [[sea sawdust]] directs here, hence bold for that --> '''''Trichodesmium''''', also called '''sea sawdust''', is a genus of [[Filamentation|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'' [[nitrogen fixation|fixes atmospheric nitrogen]] into ammonium, usable also for other organisms. While far from the only nitrogen fixing [[bacterium|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 [[heterocyst]]s, nor any other specialised cells for this task. Furthermore, nitrogen fixation peaks at mid-day, i.e. occurs during the same time as photosynthesis. Inhibitor studies even revealed that photosystem II activity is essential for nitrogen fixation in this organism. All this may seem contradictory at first glance, because the enzyme responsible for nitrogen fixation, [[nitrogenase]], is irreversibly inhibited by oxygen. However, ''Trichodesmium'' utilises [[photosynthesis]] for nitrogen fixation by carrying out the [[Mehler reaction]], during which the oxygen produced by PSII is reduced again after PSI. This regulation of photosynthesis for nitrogen fixation involves rapidly reversible coupling of their light-harvesting antenna, the [[phycobilisome]]s, with PSI and PSII. ''Trichodesmium'' forms blooms and provides substrate for many small oceanic organisms ([[bacteria]], [[diatoms]], [[dinoflagellates]], [[protozoa]], and [[copepods]]). ==References== Kana TM (1993) Rapid oxygen cycling in ''Trichodesmium thiebautii''. Limnol Oceanogr 38: 18-24 Berman-Frank I, Lundgren P, Chen Yi-B, Küpper H, Kolber Z, Bergman B, Falkowski P (2001) Segregation of nitrogen fixation and oxygenic photosynthesis in the marine cyanobacterium ''Trichodesmium''. Science 294, 1534-1537 Küpper H, Ferimazova N, Šetlík I, Berman-Frank I (2004) Traffic lights in ''Trichodesmium'': regulation of photosynthesis for nitrogen fixation studied by chlorophyll fluorescence kinetic microscopy. Plant Physiology 135(4), 2120-2133 ==External links== *[http://charles-darwin.classic-literature.co.uk/the-voyage-of-the-beagle/ebook-page-08.asp Charles Darwin's description of sailing through a ''Trichodesmium'' bloom] *[http://research.myfwc.com/features/view_article.asp?id=22896 Trichodesmium in Florida — 2004], Florida Fish and Wildlife Conservation Commission [http://research.myfwc.com/ Fish and Wildlife Research Institute] <!-- on the name "sea sawdust" --> [[Category:Cyanobacteria]] {{bacteria-stub}} [[vi:Tảo Trichodesmium]]