Types Of Cyanobacteria Toxins & Mechanism Of Action

What is it?

Cyanobacteria are a phylum of bacteria that photosynthesize. Cyanobacteria are thought to be the microbes responsible for creating an oxygenated atmosphere ~3 billion years ago. These microbes are also known as blue-green algae because of their color. They are mostly found in freshwater but can also be found in marine ecosystems (Azevedo et al. 2002).

Importance for research

Cyanobacteria have been found to create cyanotoxins. The actual toxin is usually released from the cell upon cell death or cell lysis, but it can be excreted from the cell via extracellular waste over time. Not all of the cyanobacteria produce toxins, but some can produce more than one toxin at a time (Carmichael et al. 2001). The accumulation of these toxins can deteriorate water quality and impact all levels of the food chain. Health effects have been found in animals and humans.

Where are cyanobacteria found?

Cyanobacteria can be found in in-land waters amd are capable of forming microbial mats on water surfaces. These bacteria are most commonly found in eutrophic lakes that have an increase in photosynthetic organisms compared to oligotrophic lakes. Higher temperatures increase the metabolic processes of these organisms and can lead to algal blooms. Since these are organisms that require light, they are found in the epilimnion. Human activity and global warming are increasing the concentrations of cyanotoxins globally (Rapala et al. 1997).

The three main types can be classified as hepatotoxins, neurotoxins, and lipopolysaccharide endotoxins. The main cyanotoxin that I will discuss is the most commonly seen hepatotoxin, Microcystins (MCs). Microcystin-LR has been found to be the most harmful strain of microcystins (MacKintosh et al. 1990). There are fifty known strains of microcystin.

This toxin can become an issue at the cellular level in organisms at certain doses. Cellular proteins can have excessive phosphoryalation due to protein phosphorylase inhibition (Rapala et al. 1997). PP1 and PP2A are enzymes that are found in many mammals and plants. These enzymes are inhibited from dephosphorylating proteins. Cellular processes, such as cell growth and differentiation, communication, cytoskeletal properties and gene expression are impacted due to PP1 and PP2A inhibition (MacKintosh et al. 1990). The interruption of proper protein phosphorylation can have such an impact on cell function that it can be lethal to organisms

Environmental Impacts

Concentration of microcystin can have extreme effects on the food chain. Fish and certain crustaceans have been found to have high, unsafe concentrations of microcystin in their organs. Some organisms can consume the cyanotoxin producers directly or become exposed through various mechanisms. Fish can consume the toxin in their diet, but the toxin can also diffuse through their gill openings. Other animals, including humans, can drink water containing the toxin or consume organisms that have already been exposed to the toxins. Humans can eat a fish with high concentrations of microcystin. The process can continue throughout many different levels of the food web (Magalhaes et al. 2003).

Human health effects

A dialysis center in 1996 in Brazil had a contaminated water source which contained high concentrations of the phytoplankton, microcystin. The contaminated water was being used as not only a drinking source but for also in the solutions used in the dialysis bag solutions that were entered via I.V. to all patients. 100 dialysis patients experienced acute liver failure. 52 of the patients cause of death was due to intravenous exposure to microcystin (Azevedo et al 2002). This event has sparked more research on cyanotoxins in general and has created standards and regulations that prevent the accumulation of cyanotoxins in bodies of water.

Diseases related to microcystin

Microcystin have been found to cause death by liver failure/liver hemorrhage within a few hours of an acute dose. The toxin inhibits protein phosphatases enzymes. Microscopically, liver cells with microcystin concentrations in rats and humans are seen with structure deformity and signs of apoptosis and necrosis (Pouria et al. 1998).

Cyanotoxin Accumulation Preventiona

Monitoring nutrient abundance in the watershed can be helpful in determining accumulation of cyanotoxins and growth prevention. Phosphorus stimulates the growth of cyanotoxins at a much higher rate than other nutrients such as nitrogen. Many water treatment plants now have safe daily-intake parameters for cyanobacteria and monitor algal blooms closely in reservoirs used for drinking water (Carmichael et al. 2001). Cooking fish and freshwater organisms properly to prevent high concentration intake have been promoted by health organizations around the world.

Literature Cited:

1. Azevedo S.M.F.O, W.W. Carmichael, E.M. Jochimsen, K.L. Rinehart, S. Lau, G. Shaw, G. Eaglesham. 2002. Human intoxication by microcystins during renal dialysis treatment in Caruaru-Brazil. Toxicology 181-182: 441-446.
2. Carmichael W.W, S.M.F.O. Azevedo, J.S. An, R.J.R. Molica, E.M.Jochimsen, S. Lau, K.L. Rinhart, G.R. Shaw, G.K Eaglesham. 2001. Human fatalities from cyanobacteria: chemical and biological evidence for cyanotoxins. Environmental Health Perspectives 109(7): 663-668.
3. MacKintosh C., K.A. Beattie, S. Klumpp, P. Cohen. G.A. Codd. 1990. Cyanobacterial microcystin-LR is a potent and specific inhibitor of protein phosphatases 1 and 2A from both mammals and higher plants. Federation of European Biochemical Societies 264(2): 187-192.
4. Magalhaes V.F., M.M. Marinho, P. Domingos, A.C. Oliveira, S.M. Costa, L.O. Azevedo, S.M.F.O. Azevedo. 2003. Microcystins (cyanobacteria hepatoxtoxins) bioaccumulation in fish and crustaceans from Sepetiba Bay (Brasil, RJ). Toxicon 42(3): 289-295.
5. Pouria, S., A. Andrade, J. Barbosa, R.L. Cavalcantia, V.T.S. Barreto, C.J. Ward, W. Preiser, G. Poon, G. Neild, G. Codd. 1998. Fatal Microcystin intoxication in haemodialysis unit in Caruaru, Brazil. The Lancet 352(9121):21-26.
6. Rapala J., K. Sivonen, C. Lyra, S.I. Niemela. 1997. Variation of microcystins, cyanobacterial hepatotoxins, in Anabaena spp. as a function of growth stimuli. Applied and Environmental Microbiology 63(6): 2306-2212.