Cyanobacteria and their toxins

(endorsed 2011)

General description

Cyanobacteria are Gram-negative bacteria that contain chlorophyll. The presence of chlorophyll allows them to undertaken photosynthesis, hence their historical identification as blue-green algae. Their primary health significance is that many species of cyanobacteria produce toxins, which can be either contained intracellularly, or expressed extracellularly and therefore present in the surrounding water.

Monitoring programs developed by water suppliers are typically based in the first instance on detecting the presence of cyanobacteria. These tests are generally more sensitive and less expensive than tests for toxins. Testing for toxicity is generally not implemented until cell numbers are in the 1000s per mL.

The two main types of toxin are:

• Cyclic peptides (microcystins and nodularin). Microcystins cause damage to the liver and are possibly carcinogenic. Nodularin has an identical mode of action to microcystin in animals and is considered to present at least the same risk to human health as microcystin.

• Alkaloids (neurotoxins and cylindrospermopsin). Neurotoxins produced by cyanobacteria include anatoxin a, anatoxin a-s and the saxitoxins. Only saxitoxins have been detected in Australian waters.

Cylindrospermopsin is a general cytotoxin that blocks protein synthesis. The major pathological effects are damage to the liver, kidneys, lungs, heart, stomach, adrenal glands, the vascular system, and the lymphatic system. Acute clinical symptoms are kidney and liver failure.

The table below lists potentially toxin-producing cyanobacteria found in freshwater.

Cyanobacteria	Toxin(s) produced
Cylindrospermopsis raciborskii, Aphanizomenon ovalisporum, Aphanizomenon flos-aquae, Raphidiopsis curvata, and Umezakia natans.	Cylindrospermopsins Cylindrospermopsis raciborskii is the most common producer of cylindrospermopsins in Australian water sources.
Microcystis, Anabaena, Planktothrix (Oscillatoria), Nostoc, Anabaenopsis and Radiocystis	Microcystins Microcystis sp. and M. aeruginosa in particular is the most common producer of microcystins in Australian water sources.
Nodularia spumigena	Nodularins
Anabaena, Lyngbya, Oscillatoria, Cylindrospermopsis, Cylindrospermum, and Aphanizomenon	Saxitoxins, anatoxin-a and anatoxin-a(s) In Australia neurotoxin production appears to be limited to saxitoxins from Anabaena circinalis (Velzeboer et al. 2000).

Being Gram-negative bacteria, all cyanobacteria contain lipopolysaccharides in their cell walls. The lipopolysaccharides can have inflammatory and irritative effects if contact exposure occurs, and have also been proposed as a causative agent for allergic reactions observed in sensitive individuals (skin rashes, eye irritations etc). A study in Australia indicated that about 12% of the population could be sensitive (NHMRC 2008).

The rest of this section contains detailed Fact Sheets on the specific toxins produced by cyanobacteria in Australian freshwaters, arranged in alphabetical order by toxin.

References

National Health and Medical Research Council (2008). Guidelines for Managing Risks in Recreational Water. Commonwealth of Australia.

Velzeboer RMA, Baker PD, Rositano J (1998). Characterisation of Saxitoxins Produced by the Cyanobacterial Genus Anabaena in Australia. UWRAA Research Report No. 135. Urban Water Research Association of Australia, Melbourne.