Poisonous Plants, Fungi, and Algae

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Poisonous Plants, Fungi, and Algae

• III - Algal Toxins

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Kingdom Monera

• Cyanobacteria - blue green algae
• Photosynthetic, prokaryotic organisms
• Found in oceans, fresh water, and terrestrial
  environments
• Microscopic unicells, filaments, and colonies
• Used as a food source Nostoc, Spirulina (since
  ancient times - today protein additive)
• Toxins can cause problems during blooms

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Nostoc
Oscillatoria
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Kingdom Protista

• Six divisions of algae
• Division Pyrrophyta - dinoflagellates
• Division Chrysophyta - diatoms
• Division Euglenophyta - euglenoids
• Division Chlorophyta - green algae
• Division Rhodophyta - red algae
• Division Phaeophyta - brown algae

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Dinoflagellates

• Unicellular algae covered with cellulose plates
  giving an armored appearance
• Important to the food chain in marine and fresh
  water
• Some marine species cause Red Tides
• Bloom conditions
• Color the water red
• Produce powerful toxins
• Pfiesteria newly recognized problem

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Dinoflagellates
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Diatoms Golden Brown Algae

• Diatoms abundant and important economically
• Important to the food chain in marine and fresh
  water
• Unicells with silicon-based wall with pits,
  grooves

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Green Algae

• Contains many morphological types
• Abundant and diverse in fresh water
• Play a significant role in aquatic food chains
• Seasonal blooms of green algae are often
  noticeable in ponds and lakes
• Gave rise to the land plants over 400 million yrs
  ago

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Red Algae

• Seaweeds - large multicellular marine algae
  occurring in coastal waters often attached to
  rocks
• Highly branched filaments with a feathery
  appearance or sheet-like
• Many used as a food source
• Carrageenan and agar cell wall carbohydrates
  used as stabilizing agents

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Brown Algae

• Seaweeds - large multicellular marine algae
  occurring in coastal waters often attached to
  rocks
• Huge kelps form extensive underwater "forests"
  off the California coast - among the largest
  plants on Earth
• Rockweeds commonly found in the intertidal zone
  in coastal areas - east coast and west
• Complex form holdfast, stipe, and blade
• Many used directly as a food source
• Alginic acids (alginates)

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KELP - common name for several brown seaweeds
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Drugs from the Sea

• Many types of algae, especially red and brown
  used medicinally
• Recent interest in two areas
• Anti-cancer compounds -- several dinoflagellate
  species
• Anti-viral compounds - (including anti-HIV and
  anti-Herpes many algal polysaccharides,
  especially from red and brown algae and
  cyanobacteria

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Algal Blooms and Harmful Algal Blooms

• Many different types of algae can produce an
  algal bloom
• Naturally due to nutrient up-welling but may be
  due to human sources of nutrients
• Can lead to eutrophication, oxygen depletion and
  death of ecosystem
• Blooms especially harmful when the algae are
  capable of producing toxins
• Main toxin formers Cyanobacteria,
  Dinoflagellates, Diatoms

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Algal Bloom
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Toxic Cyanobacteria

• In fresh water environments, major problems have
  been caused by toxin-producing cyanobacteria
  which are responsible for deaths of large
  populations of wild and domestic animals
• Migrating ducks and geese as well as cattle and
  sheep have been poisoned after consuming water
  contaminated with toxic cyanobacteria

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Toxic Cyanobacteria

• Normally algal cells only release the toxins when
  the cells die or when they age and become leaky
• Poisoning typically occurs when animals ingest
  whole cells
• If water is treated to break up a bloom, it is
  possible for fatal levels of the toxin to be
  released
• 12 genera of cyanobacteria known to be
  toxin-producers.
• Two of the most toxic - Anabaena and Microcystis.

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Types of toxins

• Two groups of toxins in the cyanobacteria
• Neurotoxins - alkaloids - nervous systems
• Anatoxins - Very fast death factor
• Saxitoxins
• Hepatotoxins - cyclopeptides - target the liver
• Microcystins
• Nodularin

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Anabaena

• Anabaena - a genus of filamentous N2-fixing
  cyanobacteria
• Known for producing a suite of cyanotoxins which
  range from the neurotoxic anatoxins and
  saxitoxins to the hepatotoxic microcystins.
• Genus can be found throughout the world

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Anabaena
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Microcystis

• Microcystis spp. are single-celled, colonial,
  freshwater cyanobacteria
• World-wide distribution
• Microcystins (hepatotoxins) are main toxin type
• M. aeruginosa and M. viridis appear to be the
  most common microcystin-prodcuing species.

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Microcystis
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Anatoxins

• Group of neurotoxic alkaloids produced by a
  number of cyanobacterial genera including
  Anabaena, Oscillatoria and Aphanizomenon
• Anatoxin - a - one of the most toxic of this
  group, can be lethal within 4 minutes after
  ingestion, depending on the quantity
• This led to the compound being dubbed "Very Fast
  Death Factor."

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Anatoxin-a
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Anatoxins

• Affects nervous system, often causing death due
  to paralysis of the respiratory muscles
• Acetylcholine mimic - irreversibly binds the
  nicotinic acetylcholine receptor (NAChR)
• Na channel locked open, and the muscles become
  over-stimulated, fatigued and then paralysed.
• When respiratory muscles become affected,
  convulsions occur due to a lack of oxygen in
  brain
• Suffocation the final result a few minutes after
  ingestion of the toxin

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Saxitoxins

• Neurotoxic alkaloids produced by both marine and
  freshwater algae
• In freshwater, blue-green algae, especially
  Anabaena circinalis, manufacture the toxins and
  may transfer them to freshwater shellfish or just
  poison the water
• In the oceans, dinoflagellates, especially
  Alexandrium spp, produce saxitoxins which are
  accumulated by mollusks feeding upon them

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General Structure of Saxitoxin
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Saxitoxins

• Bind to and block the sodium channel on neurons,
  inhibiting the passage of Na
• Causes muscles to relax and may lead to
  respiratory failure
• Victims experience tingling and numbness of the
  mouth, tongue, face and extremities
• Nausea and vomiting may accompany the above
  symptoms.
• In severe cases, patients will exhibit advanced
  neurological dysfunction and paralysis

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Hepatotoxins

• More widespread and have caused problems
  throughout the world
• Cyclopeptides - Microcystins have 7 amino acids
  while Nodularins have 5 amino acids
• Specifically target liver cells where they
  inhibit protein phosphatases - in liver cells
  these are involved in maintenance of the
  cytoskeleton

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Microcystin
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Hepatotoxins

• Act on the cytoskeleton within the liver cells
  causing cytoskeleton to collapse because the
  balance of phosphate groups on the cytoskeletal
  proteins is disrupted - liver cells collapse
• Can be fatal by causing blood to pool in the
  liver
• Increase tumor development and may be responsible
  for the high rates of liver cancer in parts of
  China where blooms frequently occur.
• Used in research to understand the basic
  functioning of the cytoskeleton

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Other Toxins

• Less deadly toxins are responsible for conditions
  such as "swimmer's itch"
• Toxins of several marine cyanobacteria cause this
  form of contact dermatitis characterized by
  swelling and inflammation of mucus membranes and
  redness of the skin

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Dinoflagellates and Red Tides

• Under certain environmental conditions
  dinoflagellates undergo a population explosion
• Containing up to 20 million organisms per liter
• They color the water red, orange, yellow, brown
  or any hue in-between
• Called Red Tides
• Frequently occurred in the Gulf of Mexico and
  other coastal areas

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Red Tides

• Several species of dinoflagellates, especially
  Gymnodinium breve, Alexandrium spp, produce
  powerful toxins that can cause massive fish kills
• As schools of fish swim through a bloom, the
  dinoflagellates may be disrupted or killed,
  releasing neurotoxins into the water
• The toxins damage the gills or suppress heart
  rate and result in asphyxiation - hundred or
  thousands of dead fish wash up on beaches

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Other Problems

• In other instances, the toxins accumulate in
  various filter feeding shellfish
• When the shellfish are eaten the toxins can
  affect humans
• Cause various syndromes depending on the
  dinoflagellate and type of toxin

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Dinoflagellate Poisonings

• Paralytic Shellfish Poisoning (PSP)
• Diarrhetic Shellfish Poisoning (DSP)
• Neurotoxic Shellfish Poisoning (NSP)
• Ciguatera Fish Poisoning (CFP)
• Pfiesteria piscicida

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Paralytic Shellfish Poisoning - PSP

• Dinoflagellates - Alexandrium spp, Gymnodinium
  spp, and Pyrodinium spp
• Toxins involved - saxitoxins
• As already described for cyanobacteria - can
  cause death due to respiratory arrest

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Neurotoxic Shellfish Poisoning

• Dinoflagellate - Gymnodinium breve
• Toxin - Brevetoxins
• Large lipophilic polyether toxins
• Gastrointestinal and neurological symptoms
• Causes fish kills but usually not deadly for
  people
• Aerosol exposure from sea spray has resulted in
  respiratory problems in humans

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Brevetoxin
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Ciguatera Fish Poisoning - CFP

• Dinoflagellates - Gambierdiscus toxicus
• Toxins - ciguatoxin and maitotoxin
  
• Produce gastrointestinal, neurological and
  cardiovascular symptoms from eating contaminated
  fish
• Toxins isolated from the flesh and viscera of
  various tropical and subtropical fish
• Paralysis and death have occurred but usually
  symptoms are less severe

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Ciguatoxin
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Ciguatoxin

• Fish are unaffected
• People eating contaminated fish experience
  nausea, vomiting, and diarrhea and develop
  bizarre neurological symptoms that can be
  long-lasting
• Cardiac - arrhythmias and low blood pressure
• Dizziness, muscular weakness, reverse sensations
  such as hot objects feeling cold to the touch

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Pfiesteria piscicida

• Pfiesteria piscicida implicated as the organisms
  responsible for recent fish kills and fish
  disease
• Since the early 1990s toxins produced by
  Pfiesteria may have killed over one billion fish
  in North Carolina alone with other outbreaks
  along east coast
• Toxins not identified yet
• People exposed to toxins have developed skin and
  neurological problems

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Pfiesteria

• Complex life cycle
• Appears to be around 24 different stages in the
  life cycle with flagellated, amoeboid, and
  encysted stages
• Only 3 stages appear to form toxins

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Pfiesteria

• Normally feed on bacteria and algae but produces
  toxins from certain environmental stimuli
  including the presence of excretion products from
  fish
• Toxins stun the fish and injure the fish skin
  causing them to lose the ability to maintain
  their internal osmotic balance
• As the skin is destroyed, open bleeding sores
  develop and even hemorrhaging can occur
• This often leads to death of the fish within hours

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Pfiesteria

• When the fish become incapacitated, Pfiesteria
  piscicida feed on the epidermal cells, blood, and
  other fluids that leak from the open sores
• Pfiesteria differs from other toxic
  dinoflagellates since it appears to release the
  toxins to immobilize fish and then feed off the
  fish
• Dinoflagellates responsible for other Red Tides
  release their toxins only when the cells die and
  break apart

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Pfiesteria

• Several people who work with laboratory cultures
  of Pfiesteria have suffered adverse health
  effects
• In addition fishermen, water skiers and others
  utilizing waterways where fish kills had occurred
  reported various symptoms including rashes, skin
  lesions, headache, eye irritation, and memory
  loss
• Statistically impaired learning decrease in
  exposed fishermen (and others) compared to
  control group
• Although there have been no reports of sickness
  due to eating contaminated fish or shellfish,
  people are being warned about handling fish with
  lesions

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Pfiesteria

• Toxin not identified yet
• When Pfiesteria cells were injected
  subcutaneously into rats, they showed persistent
  learning impairments
• Studies have identified the neurotransmitter
  receptor that is the likely target for these
  still unidentified toxins N-methyl-D-aspartate
  receptor rat brain receptor involved in
  cognitive function