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The phyllum Cyanobacteria is also referred to as blue-green algae (or blue green bacteria, cyanophyceae, cyanophycota, cyanophyta, oxygenic photosynthetic bacteria, oxyphotobacteria, cyanophytes). Toxins produced by some members of the group can cause human illness, that is potentially hard to recognise[1]. For example palytoxin poisoning from soft corals common in aquaria would require the exposure to be correlated with potentially non specific symptoms such as rhinorrhea, coughing, myalgia, weakness, muscle cramps and spasms, nausea, paresthesia, ataxia, and tremors not all of which might be present at one time[2].

They are (or include) a group of photosynthetic bacteria that are sometimes referred to as 'pond scum.' While they are commonly, blue-green in colour, as their name suggests, they can also be blue, green, reddish-purple, or brown.

There are many species, including Anabaena, Aphanizomenon, Microcystis, and Planktothrix spp.

Blue-green algae generally grow in lakes, ponds, and slow-moving streams when the water is warm and enriched with nutrients like phosphorus or nitrogen. In some conditions - usually in summer - they grow very quickly. As most species are buoyant, they tend to float to the surface where they can form a visible "algal bloom". Different species may be found in the same body of water; and if blooms occur more than once, they may be caused by the same or different species.

Many species cyanobacteria produce toxins, which can kill animals exposed to them. The toxins are naturally produced chemical compounds that are produced inside the cells (endotoxins) of certain species of blue-green algae. These chemicals are not produced all of the time, and there is no easy way to tell when blue-green algae are producing them and when they are not. When the cells are broken open, the toxins may be released. Sometimes this occurs when the cells die off naturally and they break open as they sink and decay in a lake or pond. Cells may also be broken open when the water is treated with chemicals meant to kill algae, and when cells are swallowed and mixed with digestive acids in the stomachs of people or animals.

For more information see the moderator's comments in this ProMED-mail post and the links therein.[3]



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