What Are Cyanobacterial Toxins (Cyanotoxins)? All are secondary metabolites of cyanobacteria....

What Are Cyanobacterial Toxins

(Cyanotoxins)?• All are secondary metabolites

of cyanobacteria.• Cyanotoxins grouped into 2

categories:– Cytoxins– Biotoxins

Cytotoxins pose no significant threat to human health

Types of Cyanobacteria Known to Have Toxic Properties

Nineteen genera comprising 41

speciesBest characterized by genera such

as;• Anabaena• Aphanizomenon• Cylindrospermopsis• Gloeotrichia• Lyngbya• Microcystis• Nodularia• Oscillatoria

Two Main Categories of Cyanobacterial

Biotoxins•Neurotoxins •Hepatotoxins

Cyanobacterial Neurotoxins Can

• Cause neuronal depolarization

• Inhibit cholinesterase• Or block neuronal ion

channels• All are fast acting, relatively

small molecules.

Implicated Species & Strains of Neurotoxin-

Producing Cyanobacteria

•Anabaena•Aphanizomenon•Nostoc•Oscillatoria•Trichodesmium

Anatoxin-a

• Produced by Anabaena flos-aquae

Anatoxin-a (cont.)

• Powerful depolarising neuromuscular blocking agent.

• Small making it rapidly absorbed by the oral route.

• Long-lasting neuromuscular blockade making an antidote unlikely.

• LD50 is 200 ug/kg body weight (i.p. mouse).

Homoanatoxin

• Produced by Oscillatoria rubescens.

Homoanatoxin (cont.)

• A methylene homologue of anatoxin-a and generally less toxic.

• May be biosynthesized from carboxylic acids present as pollutants.

• LD50 of 350 ug/kg (i.p. mouse)

Anatoxin-a(s)

• Produced by Anabaena sp.

Anatoxin-a(s) (cont.)

• Ten times more lethal than anatoxin-a.

• Different symptoms most notably severe salivation.

• Potent, irreversible cholinesterase inhibitor.

• LD50 of 20ug/kg body weight (i.p. mouse); survival time of 10-30 mins.

Cyanobacterial Hepatotoxins

• Most common of the cyanotoxins.

• All are cyclic peptides.• Can damage the liver by

deranging the cycloskeletal architecture of hepatocytes.

• Death can occur anywhere from 10 minutes to a few days depending upon dose, size of animal, species, etc…

Implicated Species & Strains of Hepatotoxin-Producing

Cyanobacteria

• Anabaena• Cylindrospermopsis• Microcystis• Nodularia• Nostoc• Oscillatoria

Microcystins

• Produced by strains of Microcystis, Anabaena, Nodularia, Nostoc, and Oscillatoria (several strain-specific variants).

Microcystin (cont.)

• All microcystins are highly stable and persistent in the environment.

• Stable at elevated temperatures for extended periods and resistant to boiling.

• They are non-volatile, dialysable, resistant to changes in pH, and soluble in water, ethanol, and acetone.

Microcystins (cont.)

• Dried crusts have been shown to be highly toxic after 6 months of drying.

• Shown to be highly toxic 21 days after treatment with copper sulfate.

• Unusual amino acid composition means there are few, if any, organisms possessing enzymes for their breakdown.

Microcystins (cont.)

• Potent inhibitors of protein phosphatases

• Most toxicities in the range of 60-70 ug/kg LD50 (i.p. mouse).

• Symptoms may include; pneumonia, sore throat, headache, dry cough, diarrhea, vomiting, blistered mouths, abdominal pain, and tender hepatomegaly.

Environmental Factors Instigating Cyanotoxin

Prevalence. • #1 causative factor world-

wide is increasing eutrophication.

• Higher instances of bloom-formation and cyanobacterial dominance = increased chances of toxin production.

• The mosaic nature of bloom formation is further complicated by the unpredictable nature of the toxicity of any given bloom.

• Any bloom should be considered potentially dangerous and suspect at all times.

• In Australia, 66% of reservoirs have seasonal cyanobacterial blooms.

• 60% of these blooms were found to be toxic.

• 88% of taste and odor episodes had some degree of toxicity associated with them.

Mitigation

• Best done through source-water protection and monitoring.

• Remediation techniques(s) recommended through monitoring efforts must be accompanied with an understanding of the ecology of the system in question.

Remediation efforts should be focused upon decreasing

eutrophication and “pushing” the system to an earlier trophic

state.

Local Case Example of Increasing Eutrophication & Cyanobacterial Dominance

• Bloom of Microcystis sp. in Roosevelt Reservoir in May 2001.

• A month later, the bloom had spread throughout Apache Reservoir.

• 2-3 weeks later, dead Corbicula flumineae and some dead fish in the upper reaches of Saguaro Reservoir.

Analytical Results

• Performed by Dr. Gregory Boyer (SUNY).

• Microcystins (by protein phosphatase inhibition assay), 2.57 ug/L in water.

• Anatoxin-a (by HPLC), 140 ug/L in water and 0.68 ug/g in corbicula tissue.

•WHO threshold for microcystin is 1 ug/L.

•Australia has an advisory limit for anatoxin-a of 3 ug/L.

Microcystis sp.

Oscillatoria sp.

Aphanizomenon sp.