Basic Biology

Cyanobacteria

Blue-Green Algae are really a type of bacterium that act like algae because they are distant relatives.  These types of bacteria are called cyanobacteria, and are partial ancestors to modern algae and all land plants.  This means that like plants and true algae, cyanobacteria can photosynthesize, meaning they get energy from the sun.[1]

There are many species of cyanobacteria, and very few are dangerous.  The most common type that is dangerous is called Microcystis, and it is dangerous because it excretes a toxin when it dies.[2]  This is the type that causes the toxic blooms in Lake Erie.  Most types are harmless, and a few may even have health benefits, such as Spirulina.


Microcystis and Microcystin

Microcystis aeruginosa is the most common species of Cyanobacteria to bloom and cause problems (although there are a number of other species in the genus).[3]  The toxin it is known for is called Microcystin, which is a dangerous liver toxin.

Microcystins and other cyanobacterial toxins are derived from amino acids not found in eukaryotes.  This means that they can be toxic to all animals and even plants.  When a Microcystis cell dies, the contents of the cell, including the toxins, are released into the surrounding water.  Some species have toxins on the outside of their cells, meaning that even living cells will release toxins.

Microcystis image

From the Algae Resource Database


Types of Algae

A variety of different organisms fall under the category called algae, all of them named after a general color.  There are green algae, red algae, brown algae, and blue-green algae.  Blue-green is the most different because while the others are plants or close relatives of plants, this type is actually a kind of bacterium.[4]

Green: Closely related to land plants.  
Phylum: Chlorophyta.  
Consists of seaweed and others.

Red: Related to Green Plants (algae and land), but distinct.  
Phylum: Rhodophyta (disputed).  
Consists of seaweed and others.

Brown: Kingdom Chromalveolata.  
Kelp and diatoms, golden algae and dinoflagellates (red tide).
Related to the plant kingdom, and also containing chloroplasts.

Blue-Green: Bacteria, specifically a phylum called cyanobacteria.
Related to chloroplasts which allow all plants and algae to 
photosynthesize.

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