Trichodesmium (McMahon)

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Classification

Kingdom: Bacteria Domain: Phylum: Cyanobacteria Class: Order: Oscillatorialis Family: Genus: Trichodesmium

Description

Trichodesmium thiebautii [1F]

Trichodesmium is a filamentous genus of cyanobacteria found in the open ocean. They can grow in solitude but are often found in filamentous colonies (called trichomes) that are a few millimeters in length. Trichodesmium form huge blooms in the open ocean that can extend for hundreds of kilometers. It thrives in nutrient-poor environments and is known for aerobically fixing atmospheric nitrogen.

This species was first described off the coast of Australia by Captain Cook in the 18th century. It is most related genetically to other marine cyanobacteria, including Synechococcus, Crocosphaera, and Anabaena. The species that has been completely sequenced, Trichodesmium erythraeum, has 7750108 base pairs and a 34% G-C content. It is available in pure culture (although it is difficult to grow) and is a photoautotroph (nitrogen fixing, photosynthetic bacteria).

Ecology and Significance

Trichodesmium is the main contributor of new nitrogen to the euphotic zone of marine waters, adding up to 30 mg/m2/day of ammonium to the ocean. It is widespread in tropical and subtropical oceans and is also a contributor of CO2 fixation through photosynthesis. It is often found in nutrient-poor (oligotrophic) environments near the surface and is often visible from above the water as huge, filamentous colonies. Blooms often occur in the summer in warm areas with low nitrogen.

Trichocesmium, like other cyanobacteria, produces neurotoxins that can be harmful to animals such as fish and oysters in the ocean such as fish at high enough levels. They have also been known to cause illness to humans both directly through contact and indirectly through consumption of animals laced with Trichodesmium neurotoxin. These large, harmful blooms are expected to increase in the future as nutrient (phosphorus) loading and global warming from human activity create a more optimal environment for cyanobacteria.


Metabolism

The metabolism of Trichodesmium is very interesting to scientists who study marine nutrient cycling because it is the greatest contributor of useable nitrogen to the ocean. Its metabolism is particularly interesting because it is one of the only diazotrophic bacteria that fixes atmospheric nitrogen during the daytime without the use of a heterocyst. Usually cyanobacteria have to either separate photosynthesis and nitrogen fixation using heterocysts or must undergo each process at different times of day. This is because the enzymes used to fix nitrogen are inhibited by oxygen. However, this genus performs both photosynthesis and nitrogen fixation during daylight hours. It is not confirmed how these bacteria are able to do both things without heterocysts and is an exciting area of research for microbiologists studying nitrogen fixation in aquatic environments.

References

Capone, Douglas G., et al. "Trichodesmium, a Globally Significant Marine Cyanobacterium." Science 276.5316 (1997): 1221-29. Print.

Webb, Eric. "Trichodesmium." Woods Hole Oceanographic Institute. www.whoi.edu. 2002. Web.

Yang, Yu et al. “Comparison of Envelope-Related Genes in Unicellular and Filamentous Cyanobacteria.” Comparative and Functional Genomics 2007 (2007): 25751. PMC. Web. 14 May 2015.


Author

Page authored by Rebecca LeBeau, student of Prof. Katherine Mcmahon at University of Wisconsin - Madison.