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 species
Best 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 NeurotoxinProducing 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 anatoxina.
• 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 worldwide is increasing
eutrophication.
• Higher instances of bloomformation 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.