Toxic Fungi and Mycotoxins

Many fungi produce compounds toxic to other organisms, these are secondary metabolites
Mycotoxins are toxic to animals, humans, and plants
Secondary metabolites are often produced at the end of the exponential growth phase in batch culture or when growth is substrate-limited in continuous culture

Fungal poisoning due to mycotoxins can occur in two ways:
- Mycotoxicosis: Poisoning by toxins of microscopic fungi (micromycetes), which grow on grains, food products and animal feed.
- Mycetism: Intoxication from eating fruiting bodies of mushrooms (macromycetes) due to misidentification.

Over 400 different mycotoxin metabolites are known
Mycotoxins are non-protein substances, including heterocyclic compounds, aliphatic hydrocarbons, indoles, and alkaloids.
Low molecular weight (less than 1000 daltons) making detection difficult.
Stable and hard to destroy by processing or boiling.
Cause chronic effects, and even at low concentrations, they can be carcinogenic, mutagenic, teratogenic, and immuno-, hepato-, nephro-, and neurotoxic.
Mycotoxins are potent cell poisons.
Mycotoxicology is an independent science, developed after the discovery of aflatoxins (1960).
Mycotoxins affect up to 25% of global food and feed crop output.

Mycotoxin contamination of crops is influenced by host plant susceptibility and geographic/climatic conditions.
Fungi are categorized into field and storage fungi.
- Field fungi (e.g. Claviceps, Fusarium) produce mycotoxins on plants before harvest
- Storage fungi (e.g. Aspergillus, Penicillium) produce mycotoxins in the postharvest stage during storage, processing, and transport
Mycotoxins enter the body through the respiratory tract and through food.

Taxonomy: Class Sordariomycetes in Ascomycota
This fungus affects rye, wheat, and barley (rarely oats)
It causes ergot, with a high concentration of the alkaloid ergotamine. Ergot is the French name for a cock's spur
Ergotamine is a complex molecule with a tripeptide-derived cyclol-lactam ring linked to a lysergic acid moiety.
Other alkaloids (7) are found in the ergoline group
Can cause ergotism. Ergotism is a serious disease of humans or animals due to ingesting ergot alkaloids found in plant matter, especially in ergot-contaminated grains.
Ergotism was rare in the 21st century but had recurring historical outbreaks.
Two forms of ergotism:
- Gangrenous ergotism: Affects the blood vessels, which leads to vasoconstriction of vessels and gangrene.
- Convulsive ergotism: Affects the nervous system, characterized by hallucinations, irrational behavior, convulsions, and other symptoms.
Monks in the medieval ages used balms and plant extracts to treat symptoms of ergotism.
Some ergot alkaloids have medical uses, e.g. to relieve migraine and to control hemorrhaging. In high doses, ergot alkaloids can be chemically modified to produce the hallucinogenic drug, LSD.

Taxonomy: Class Sordariomycetes in Ascomycota
Cosmopolitan (in soils from the permafrost to the Sahara)
Economically important toxigenic species
Causes various plant diseases, including head blight of wheat, barley, and oats, and maize ear rot,
Produces mycotoxins such as zearalenone, fumonisin, and trichothecenes.
Mycotoxin contamination of food can lead to livestock diseases and potentially carcinogenic mycotoxins for humans.

Taxonomy: Class Sordariomycetes in Ascomycota
Economically important fungal genera
Widespread, commonly found on stored grains, spices, peanuts, nuts, bread, dried/cured ham, pickles, jams, and preserves.
Can contaminate food causing serious mycotoxins such as aflatoxins (B1, B2, G1, G2, M1), ochratoxin A, and fumonisins.
Aflatoxins are heterocyclic compounds
Contamination can be carcinogenic and cause hepatocellular carcinoma, which is liver cancer.
Ochratoxins are potent pentaketide nephrotoxins contaminating grains, legumes, coffee, dried fruits, beer, and wine.

Mushroom poisoning is a significant form of toxin-induced disease, with approximately 50-100 deaths annually in Europe from poisoning.
Poisonous mushrooms are often called toadstools.
Classic examples of poisonous mushrooms include Amanita phalloides (death cap) and Amanita virosa (destroying angel). These contain phallotoxins and amatoxins, respectively, that are not usually classed as mycotoxins.
Many toxic mushrooms can look nearly identical to non-toxic ones, making identification critical.
Mycotoxin poisoning is categorized by the symptoms and major internal organ effects.

Taxonomy: Class Basidiomycetes in Basidiomycota
Edible when not consumed with alcohol
Contains coprine which blocks the action of acetaldehyde dehydrogenase, causing an “antabuse-like” reaction with alcohol, leading to nausea, vomiting, cramps, etc.

Taxonomy: Class Basidiomycetes in Basidiomycota
Contains amatoxins, which are very dangerous to human health.
Primarily affects the liver and kidneys, but may cause other organ damage.
Symptoms (abdominal pain, vomiting, diarrhea) do not appear until 6-24 hours after consumption.
Initial “honeymoon phase” can hide the severity of the poisoning leading to fatal consequences.

Contains psilocybin and psilocin, causing mild hallucinations and heightened sensory experiences.
Stropharia squamosa and Stropharia aeruginosa are in this group.