Alexandrium tamarense

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Alexandrium tamarense

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A Microbial Biorealm page on the genus Alexandrium tamarense


Domain: Eukaryota; Phylum: Dinophyta; Class: Dinophyceae; Order: Gonyaulacales; family: Goniodomataceae; genus: Alexandrium; species: Alexandrium tamarense

Description and significance

Alexandrium tamarense is a single-celled, phototrophic dinoflagellate which lives around coastal marine environments . It’s association with algal blooms forms red tides. A.tamarense is microscopic in size at about 25-46 micrometers in length per cell. It is often brown in color and has a spherical shape. The algal blooms caused by A. tamarense usually contains millions of these cells per liter of seawater. Each of these cells are toxic as they produce a neurotoxin that is highly toxic to organisms in that environment such as fish and shellfish. Higher animals such as humans, mammals and birds are affected through the food chain.

Genome structure

Alexandrium tamarense has a large amount of DNA compared to other eukaryotic organisms. It does not have nucleosomes. It consists of 144 chromosomes which are condensed in the nucleus until DNA replication. There is a total of 11,103 nucleotides that have been sequenced. Out of these nucleotides, 218 nucleotide are core and 10,885 are expressed sequence tags. Identification of genes that are responsible for toxin production has not yet been achieved.

Cell structure, metabolism & life cycle

A. tamarense manufacture its own food by using energy is obtains from sunlight, thus it is photoautotrophic. It is a primary producer and is a source of food for many other organisms. It moves from one position to another in water with the help of its two flagella. A. tamarense is said to be "armored" as it has a layer of cellulose that form plates known as thecae. A. tamarense is distinguished from other species in the same genus because of the presence of a ventral pore on the 1' plate, and the shape and size of its cells and thecal plates. A. tamarense reproduces mostly asexually by binary fission, but also sexually with anisogamous mating types. During sexual reproduction, gametes fuse producing a planozygote which becomes a resting cyst until environmental conditions can sustain germination. A. tamarense has the following Life cycle stages : motile vegetative cells, haploid gametes, diploid zygotes, resting cysts, and temporary cysts.

Ecology (including pathogenesis)

Although Alexandrium tamarense provides a food source for various organisms such as fish and shellfish, it is also toxic to these organisms, harming the environment and its inhabitants. Although some organisms are unaffected by these toxins, an accumulation of these toxins over can be very poisonous to higher organisms that feed on them. Consumption of infected organisms can cause different illnesses. Paralytic Shellfish toxins (PST) are caused by A. tamarense. Alexandrium tamarense can adapt quickly to different levels of nitrogen, thus it can survive in a constantly changing environment. Some of the strains of Alexandrium tamarense are not 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) and these toxins are more toxic in the resting cyst stage than in their motile stage.These toxins include gonyautoxins, neosaxitoxin and saxitoxin, and are harmful fish, marine mammals, birds, and humans. It has not yet been discovered whether toxins produced by A. tamarense provide any health benefits to humans. However, toxins created by similar dinoflagellates have already shown some benefits, for example Gonyautoxin, a paralyzing phototoxin which aids in the healing of anal fissures.

Interesting feature

It produces toxins which although harmful to humans and other organisms, has a potential use in biotechnology for healing certain diseases.

References Don Anderson WHOI, Brad Butman USGS, Peter Franks SIO, Rocky Geyer WHOI, Ted Loder UNH, Rich Signell USGS, Bruce Keafer WHOI, Derek Fong WHOI, "Toxic "Red Tide" Populations in the Western Gulf of Maine: Sources, Transport, and Nutrient Environment Effects of toxic dinoflagellate Alexandrium tamarense on the energy budgets and growth of two marine bivalves, Siu-ChungLi, Wen-Xiong Wang,and Dennis P. H. Hsieh, Department of Biology, The Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Hong Kong, People's Republic of China