Alexandrium tamarense: Difference between revisions

	;
Scientific classification
Kingdom:	Eukaryota;
Phylum:	Alveolata;
Class:	Dinophyceae;
Order:	Gonyaulacales;
Family:	Gonyaulacaceae;
Genus:	Alexandrium;
Species:	tamarense;
Binomial name
	Alexandrium tamarense;

Revision as of 17:12, 15 April 2008

Main Article

Discussion

Description and significance

Describe the appearance, habitat, etc. of the organism, and why it is important enough to have its genome sequenced. Describe how and where it was isolated.

Alexandrium tamarense is a single-celled, phototrophic dinoflagellate found in coastal marine environments throughout the world and is associated with algal blooms that result in the phenomenon known as red tides (pictured below).

At only 25-46 micrometers in length per cell A. tamarense is microscopic in size, often brown in color and somewhat spherical in shape.

The algal blooms caused by A. tamarense often result in millions of these cells per liter of seawater. Each of these cells produces a neurotoxin that is highly toxic to inhabitants such as fish and shellfish, and can be passed through the food chain to other organisms such as marine mammals, birds, and humans.

Genome structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features?Does it have any plasmids? Are they important to the organism's lifestyle?

There are many different Alexandrium species and DNA sequencing is the best way to distinguish between them.

Like other dinoflagellates, Alexandrium tamarense consists of large amounts of DNA compared to other eukaryotic organisms. It also lacks nucleosomes. It consists of 144 chromosomes which are condensed in the nucleus until DNA replication. A total of 11,103 nucleotides [218 nucleotide core and 10,885 expressed sequence tags (ESTs)] have been sequenced.

It is still not clear which genes play a role in toxin production.

Cell structure and metabolism

Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.

Like other dinoflagellate species, A. tamarense is photoautotrophic meaning it manufactures its own food by using energy is obtains from sunlight. It is considered a primary producer and is a source of food for many other organisms. It is a also motile organism, having two flagella which it uses to propel itself through water.

A. tamarense is considered "armored" because it is surrounded by a layer of cellulose that form plates known as thecae.

A. tamarense is very similar morphologically to other species in the same genus, however it can be distinguished by the presence of a ventral pore on the 1' plate, and the shape and size of its cells and thecal plates.

A. tamarense reproduces asexually by binary fission, however it can also reproduce sexually with anisogamous mating types. During sexual reproduction, gametes fuse producing a planozygote which then converts into a resting cyst until environmental conditions are sufficient for germination. Life cycle stages include motile vegetative cells, haploid gametes, diploid zygotes, resting cysts, and temporary cysts.

Ecology

Fish kill due to toxins produced by A. tamarense
Photo courtesy of Texas Parks and Wildlife Department

Many dinoflagellates provide a food source for various organisms such as fish and shellfish that feed on primary producers. Some like Alexandrium tamarense are toxic, however, and have devastating effects on the environment and its inhabitants.

While some organisms are unaffected by the toxins produced by A. tamarense, these toxins can accumulate to extremely high levels in the organisms and can be very dangerous to higher organisms that consume them. Consumption of infected organisms can lead to many different illnesses. Paralytic Shellfish toxins (PST) are the primary cause of illness by A. tamarense.

Fish that affected by this illness and also attack the central nervous system, fish are no longer able to breathe in these environments and this often leads to fish kills (pictured right)

Alexandrium tamarense is known for its ability to adapt quickly to different levels of nitrogen, making it more likely to survive in a constantly changing environment.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Not all strains of Alexandrium tamarense are toxic. Different strains are often found in the same algal blooms caused by this species.

However, some strains of Alexandrium tamarense produce very potent neurotoxins known as paralytic shellfish toxins (PSTs). These toxins, which include gonyautoxins, neosaxitoxin and saxitoxin, affect fish, marine mammals, birds, and humans.

Many deaths have been reported from the consumption of shellfish infected with these toxins.

Resting cysts can harbour PSP toxins, it was been demonstrated that cysts were more toxic than their motile stage. Humans, other mammals, fish and birds can be affected. Please consult original reference for further details. Harmful species http://www.algaebase.org/search/species/detail/?species_id=40299

http://www.nmnh.si.edu/botany/projects/dinoflag/Taxa/Atamarense.htm

==Application to Biotechnology== Does this organism produce any useful compounds or enzymes? What are they and how are they used?

While it is unclear whether toxins produced by A. tamarense provide any health benefits to humans, toxins created by similar dinoflagellates have already shown some benefits. An example of this is Gonyautoxin, a paralyzing phototoxin which aids in the healing of anal fissures.

Current Research

Enter summaries of the most recent research here--at least three required

A recent increase in harmful algal blooms produced by A. tamarense and similar species have caused concern for fisheries around the world.

Areas along the coast of Maine have had outbreaks year after year prompting a five year project which is currently underway at Woods Hole Institute's Anderson Laboratory. This project is focused on the abundance, distribution, and motility of A. tamarense in the region. (http://www.whoi.edu/redtide/labweb/projects.html)

At the Hong Kong University of Science and Technology,scientists are tried to determine the effects of A. tamarense on energy budgets and growth of two marine bivalves, the manila clam (Ruditapes philippinarum) and the green-lipped mussel (Perna viridis). They found that scope of growth and absorption efficiency decreased when these bivalves were exposed to PSP.(http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V7H-44PWXYG-2&_user=699469&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000039278&_version=1&_urlVersion=0&_userid=699469&md5=e22cc9ea0a95b7c463337a6ff596c71e)

http://www.tpwd.state.tx.us/landwater/water/environconcerns/hab/redtide/faq.phtml

http://www.publicaffairs.noaa.gov/releases2004/oct04/noaa04-r999-58.html

http://www.publicaffairs.noaa.gov/releases2004/oct04/noaa04-r999-48.html

http://en.wikipedia.org/wiki/Paralytic_shellfish_poisoning

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1173104

http://www.nmnh.si.edu/botany/projects/dinoflag/Taxa/Atamarense.htm

http://www.assurecontrols.com/info-dinoflagellates.htm

http://microbewiki.kenyon.edu/index.php/Alexandrium