Mushrooms' Deadly Attack Strategies

Mushrooms have a long history with humans, being consumed since prehistory, but also implicated in the deaths of several historical figures. Of the many mushroom species, only about 100 are toxic, and only a few of these are fatal. Poisonous mushrooms contain a variety of toxins, and symptoms of poisoning can range from mild gastrointestinal upset to organ failure and death. Interestingly, oyster mushrooms, a common variety found on pizzas, are predatory and paralyze their microscopic prey, nematodes, before digesting them from the inside.

Oyster mushrooms attack microscopic nematodes

Oyster mushrooms, or Pleurotus ostreatus, are the reproductive structures, or fruiting bodies, of a fungus that preys on microscopic nematodes. Nematodes are small, worm-like animals that are found in most environments. They are the most abundant animals in the soil, making them a natural food choice for fungi.

Oyster mushrooms have a unique strategy to catch their prey. First, they exude chemicals that attract nematodes by smelling like food. Once a nematode comes close enough, the oyster mushroom uses a weapon called a "sticky nob" or a lollipop-like structure that contains a toxin that paralyzes nematodes. These nobs stick out like spines from the fungus' hyphae. The "lollipop" structures are present on the hyphae, the long, branching structures that grow inside rotting wood and make up most of the fungus.

Once the nematode is immobilized, the oyster mushroom's hyphae grow into the nematode's body to digest it from the inside and absorb its nitrogen. Oyster mushrooms have evolved this strategy to supplement their diet because they live on dead trees, which have limited access to nitrogen-containing proteins.

Research on oyster mushrooms and their ability to prey on nematodes has been conducted by Yen-Ping Hsueh, an associate professor at the Institute of Molecular Biology in Academia Sinica, Taipei, and her colleagues. They discovered that the "lollipop" structures contain a volatile chemical called 3-octanone, which acts as a nerve gas to paralyze and kill nematodes by destroying their cell membranes.

Poisonous mushrooms can cause organ failure

Poisonous mushrooms contain a variety of toxins that differ in toxicity. Amatoxin is the most common toxin that causes severe poisoning and is found in various mushroom species. Amatoxin blocks DNA replication, leading to cell death, particularly in frequently replicating cells such as those in the kidneys and liver. This can eventually affect the central nervous system, causing loss of muscle contraction and liver failure. Amatoxin is found in mushrooms such as Amanita, or "the death cap", Galerina, and Lepiota. Despite the severe symptoms, amatoxin poisoning can be treated if quick, professional care is provided.

Another toxin, orellanine, generally causes no symptoms for 3-20 days after ingestion. By day 11, kidney failure begins, and by day 20, symptoms such as pain in the kidney area, thirst, vomiting, headache, and fatigue become evident. Mushrooms in the Cortinarius genus contain this toxin, and ingestion can lead to renal impairment, with some cases requiring kidney transplantation.

Mushrooms in the Gyromitra genus contain the toxin gyromitrin, which affects multiple body systems. Gyromitrin blocks the neurotransmitter GABA, leading to stupor, delirium, muscle cramps, loss of coordination, tremors, and seizures. It also causes severe gastrointestinal irritation, resulting in vomiting and diarrhea. Gyromitrin can lead to liver failure and red blood cell breakdown, causing jaundice, kidney failure, and anemia.

Mushrooms of the genus Omphalotus, including jack o' Lantern mushrooms, contain muscarine, which stimulates the nerves and muscles. Symptoms of muscarine poisoning include sweating, salivation, tears, blurred vision, palpitations, and respiratory failure in high doses.

It is important to accurately identify mushrooms before consumption, as some poisonous varieties can be deadly. While some rules help rule out poisonous mushrooms, the only way to ensure safety is to be 100% certain of the mushroom's identity.

Orellanine toxin causes kidney failure

Orellanine is a toxin produced by some members of the Cortinarius genus of mushrooms. It is the only known mushroom toxin that selectively targets the kidney, causing acute kidney injury (AKI) in humans when ingested. The toxin causes kidney failure and can even lead to death if left untreated.

The first signs of orellanine poisoning typically appear after 3–20 days, with symptoms similar to the common flu, including nausea, vomiting, headache, loin pains, thirst, and fatigue. This is followed by a renal phase, which occurs about 8 days after ingestion, and can lead to death in severe cases. Orellanine poisoning can result in irreversible renal damage, requiring dialysis or even kidney transplantation.

The Cortinarius species, also known as deadly webcap, can be found in forests of Northern Europe, Scandinavia, and North America. These mushrooms may be mistaken for other edible varieties, leading to accidental ingestion and subsequent kidney failure. The nephrotoxicity of C. orellanus was first recognized in the 1950s when it was identified as the cause of mass poisoning in Poland. Since then, most reports of poisoning have originated in Europe, where mushroom foraging is popular.

The mechanism by which orellanine causes kidney failure is not fully understood, but it may involve polymorphisms in genes controlling transport, bioactivation, and detoxification processes in the kidney. The delayed appearance of AKI after ingestion is a characteristic feature of orellanine poisoning, and consuming more mushrooms during this latent period can increase the toxin load and worsen the injury. Treatment for orellanine poisoning is symptomatic and relies on standard management of kidney failure.

Gyromitrin toxin causes neurotoxicity, gastrointestinal toxicity, and destruction of blood cells

The Gyromitra mushroom, also known as the "false morel", contains a toxin called gyromitrin, which is a volatile and water-soluble hydrazine compound. Gyromitrin is rapidly broken down in the stomach to form toxic hydrazines, specifically monomethylhydrazine (MMH), which is the principal toxic agent. MMH irreversibly blocks important enzymes, including cytochrome P450 enzymes, and inhibits pyridoxal phosphokinase, which is involved in the activation of pyridoxine (vitamin B6). This leads to a reduction in gamma-aminobutyric acid (GABA) synthesis and increased glutamic acid concentrations.

The neurological symptoms associated with gyromitrin poisoning include dizziness, vertigo, ataxia, sweating, headache, lethargy, stupor, delirium, seizures, and in severe cases, coma or death. These symptoms arise due to the decreased production of the neurotransmitter GABA and increased glutamic acid. Additionally, MMH causes oxidative stress, leading to methemoglobinemia, which affects the blood's ability to carry oxygen.

Gastrointestinal symptoms are common and often the initial manifestation of gyromitrin poisoning. These symptoms include nausea, vomiting, abdominal pain, and diarrhea, typically developing within 5-10 hours of ingestion. The severity and duration of these symptoms are related to the amount of toxin consumed. In most cases, gastrointestinal symptoms are self-limiting, with patients recovering within 2-6 days.

In some cases, gyromitrin poisoning can lead to liver dysfunction, renal failure, and hemolysis (destruction of red blood cells). Liver damage can result in jaundice, while kidney failure is associated with symptoms such as pain in the kidney area, thirst, and fatigue. The destruction of red blood cells can lead to anemia, further exacerbating the condition.

Amatoxin poisoning causes violent abdominal pain, vomiting, and bloody diarrhoea

Amatoxin poisoning is caused by the ingestion of certain species of mushrooms, most notably the death cap mushroom (Amanita phalloides). This deadly fungus bears a striking resemblance to edible mushrooms, leading to accidental consumption. Within 6 to 12 hours of ingestion, violent abdominal pain, vomiting, and bloody diarrhoea occur, signalling the beginning of Amatoxin poisoning. These initial symptoms are followed by a rapid loss of fluids, intense thirst, and signs of severe involvement of the liver, kidneys, and central nervous system.

The mechanism of Amatoxin poisoning involves the inhibition of RNA polymerase, which is essential for the synthesis of key proteins. As a result, hepatocytes, the liver cells, undergo pathologic centrilobular necrosis, leading to liver failure. This toxic effect of Amatoxin is not removed by dialysis, and confirmatory testing for exposure is often unavailable or unreliable. The prognosis for Amatoxin poisoning depends on the time taken to seek treatment, with early intervention resulting in rare fatalities.

The violent abdominal pain associated with Amatoxin poisoning can be understood through the toxin's impact on the liver. As the liver sustains damage, its ability to filter toxins and support digestion is compromised, leading to pain and discomfort in the abdominal region. The vomiting and diarrhoea that accompany the abdominal pain are also indicative of the body's attempt to expel the toxic substance and reduce its absorption.

Bloody diarrhoea, a particularly concerning symptom of Amatoxin poisoning, suggests the presence of blood in the stool. This can occur due to damage to the gastrointestinal tract or bleeding in other parts of the body, such as the liver or kidneys, which are common targets of Amatoxin toxicity. The bloody diarrhoea, along with vomiting, can lead to dehydration, further exacerbating the condition.

It is important to note that mushroom poisoning is a rare occurrence, and most cases involve gastrointestinal upset without long-term damage. However, Amatoxin poisoning stands out as a significant cause of acute liver failure, contributing to 95% of deaths from mushroom ingestion worldwide. Therefore, consuming wild mushrooms, especially those resembling the death cap, requires caution to prevent severe health consequences.

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