Transcript King Saud University College of Science Microbiology Department By

Cyanobacteria ~ blue-green algae
• Ancient, ubiquitous
• Created world’s oxygen atmosphere
• Ancestors of green plants
• Produce ~ 50% of the oxygen in the
atmosphere today
BUT:
• Develop excessive blooms, scums, mats
due to human pressures on water
resources
• Present economic, aesthetic, and health
problems
• Many produce potent TOXINS
• Risk management needs
Freshwater cyanobacterial blooms, a global
phenomenon
Cyanotoxins
• occur annually in water
resources, including those
used for drinking, fisheries,
recreation and tourism
• present substantial risks to
human and animal health
• are produced globally
• require to be detected and
quantified to meet guidelines
and regulations
Classes of Cyanotoxins
(1) Hepatotoxins: microcystins, nodularins
cylindrospermopsins
(2) Neurotoxins: anatoxin-a, homoanatoxin
anatoxin-a(s), saxitoxins
(3) Irritants and allergenic toxins:
aplysiatoxins,
lipopolysaccharide endotoxins
Microcystins
• Group of >80
structurally related
cyclic heptapeptides
• In acute cases death
occurs by
hypovolaemic shock
• Able to inhibit protein
phosphatases and
may affect cell cycle
• Tumour promoters
Cylindrospermopsin
• A guanidine alkaloid
hepatotoxin andgenotoxin
• Affects multiple organs
• Inhibits eukaryotic
protein translation
• Causes DNA strand breaks
• Mostly found in tropical
Saxitoxins
• A group of ~20
structurally related
alkaloids
• Bind to voltage gated
Na+ channels
• Paralysis and death
• LD50 10μg kg-1 (i.p.
mouse)
Anatoxin-a
• Small molecular
weight alkaloid that
mimics acetylcholine
• 7 structural variants
known to exist
• Structural analogue of
cocaine
• Death by paralysis
and asphyxiation
LPS endotoxins
Characteristic of Gram negative bacteria (including
cyanobacteria)
Found in the outer layer of the cell wall
The lipid A component responsible for human
health effects
Fever, vomiting, diarrhoea and inflammation
BMAA- a new
cyanobacterial toxin?
• Non-protein amino acid
• Binds to glutamic acid
receptors
• Acutely neurotoxic to
primates in high doses
• Associated with an
incidence of Motor Neuron
Disease
Genus
Anabaena
Anabaenopsis
Aphanizomenon
Cylindrospermopsis
Hapalosiphon
Lyngbya
Microcystis
Nodularia
Nostoc
Phormidium (Oscillatoria)
Planktothrix (Oscillatoria)
Schizothrix
Trichodesmium
Toxins produced
Anatoxins, Microcystins, Saxitoxins
Microcystins
Saxitoxins, Cylindrospermopsins
Cylindrospermopsins, Saxitoxins
Microcystins
Aplysiatoxins, Lyngbyatoxin a
Microcystins
Nodularin
Microcystins
Anatoxin
Anatoxins, Aplysiatoxins,
Microcystins, Saxitoxins
Aplysiatoxins
yet to be identified
* Not all species within a genus
produce
the
same
toxins.
In addition to these toxins, many
other bioactive compounds have
been isolated from cyanobacteria.
Some have been determined to be
toxic to specific organisms and are
potentially toxic to humans.
Impacts on Human Health
• Gastrointestinal upsets
(USA, Zimbabwe, UK, Australia, Sweden)
• Contact dermatitis, mucosal irritation
(Pacific Islands,UK, USA, Norway, Australia)
• Liver damage (Brazil, Australia)
• Kidney damage (Australia)
• Neurological damage (Brazil)
• Pulmonary consolidation (atypical
pneumonia, UK)
Potential Long-Term Health Effects
• Microcystins
– Tumour promotion
• Nodularin
– Tumour promotion and possible
carcinogenicity
• Cylindrospermopsin
– Carcinogenicity through effects on DNA
• BMAA
– Possible association with human
neurodegeneration
Exposure routes
• Drinking water
• Diet
• Dermal
• Pulmonary
• Haemodialysis
Human health incidents
• Itaparica Dam
– Gastrointestinal upset (2000 cases)
– 88 deaths over a 42 day period
– Microcystis and Anabaena present in
water
– Cyanotoxins thought to be the cause
• Primary liver cancer in China
– “Hot spots” related to drinking water
supply
– Surface vs. well water
CLIMATE CHANGE
internationally agreed that
cyanobacterial
Blooms will increase in geographical spread,
population density and seasonal duration
Examination of the evolutionary history of
cyanobacteria, studies of their
ecophysiology, and recent investigations of
phytoplankton dynamics and
community structure in response to global
climate change all suggest that
cyanobacteria will probably thrive under
environmental conditions associated
with global warming.
The Team