Michael Davis
Mushrooms are typically associated with vegetarian diets, but some species are actually carnivorous. Oyster mushrooms, for instance, are known to feast on roundworms, or nematodes, by poisoning and paralysing them before absorbing their slurry. This behaviour has been observed in other fungi, with some 200 species known to attack, kill and digest tiny animals. This raises questions about the ethical status of mushrooms in vegetarian and vegan diets, and suggests that mushrooms may be more sophisticated organisms than previously thought.
| Characteristics | Values |
|---|---|
| Types of carnivorous mushrooms | Oyster mushrooms, Flammulina velutipes, 200 species of fungi |
| How they poison prey | Poison drops, constricting rings, filaments |
| Prey | Nematodes, roundworms, insects, microscopic animals |
| What they eat | Meat, guts, nerves, muscles |
| Where they are found | Southwestern France, ponds, bogs, wet low-nutrient soil |
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What You'll Learn
Oyster mushrooms are carnivores
Oyster mushrooms, or Pleurotus ostreatus, are a type of carnivorous fungi. They are mild-flavoured, cream-coloured mushrooms with a scent reminiscent of anise, often used in cooking. However, despite their innocuous appearance, oyster mushrooms have a sinister side. They are one of the few vegan foods that can eat meat.
Oyster mushrooms prey on nematodes, or roundworms, which are abundant in the soil. These worms are small but complex animals with their own nervous system, muscles and digestive system. The mushrooms have a unique way of paralysing and killing their prey. They produce a toxin, or nerve gas, that is contained within lollipop-like structures called toxocysts. When emitted, this toxin causes rapid paralysis and widespread cell death in roundworms within minutes of contact. The worms' wiggling slows and then stops. The oyster mushrooms then inject their filaments into the corpses, dissolving the contents and absorbing the slurry.
Scientists have long known that oyster mushrooms feed on roundworms, but only recently discovered the specific toxin they use and how it works. In 2020, researchers at the Institute of Molecular Biology of the Academia Sinica in Taiwan observed how the toxins enter worms' bodies through the sensitive tips of the worms' small sensing organs. In 2023, a team of Taiwanese scientists discovered that the toxin targets an indispensable part of the worms, causing cell death. This mechanism of paralysis has been conserved by evolution across nematode lineages that diverged an estimated 280-430 million years ago.
Oyster mushrooms have evolved to feed on nematodes because these worms are plentiful in the soil and provide a good source of protein. The mushrooms grow on dying or dead trees, which are poor in nitrogen, so they need an alternative source of this essential element. By exuding chemical lures, oyster mushrooms are able to attract their microscopic nematode prey.
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Oyster mushrooms poison and paralyse nematodes
Oyster mushrooms, or Pleurotus fungi, are known to be carnivorous. They primarily feed on nematodes, which are tiny roundworms that are among the most abundant animals in the soil. Nematodes are high-quality sources of protein, which has likely spurred the evolution of fungi that feed on them.
Oyster mushrooms have been observed to paralyse and kill nematodes using a nerve gas called 3-octanone. This toxin is produced in a lollipop-shaped structure on the hyphae of the fungus, which are the long, branching structures that grow inside rotting wood. When a nematode touches the structure, it triggers a massive influx of calcium ions into the worm's nerve and muscle cells, causing paralysis and death. The oyster mushroom then grows its hyphae into the nematode's body to suck out its contents and absorb the slurry.
The discovery of this unique hunting mechanism has intrigued scientists for decades. In the 1980s, researchers found that oyster mushrooms were carnivorous and could paralyse and digest nematodes. However, the specific toxin and mechanism by which it worked remained unknown until recently.
A team of Taiwanese scientists conducted a study on 15 species of Pleurotus fungi and 17 species of nematodes. They discovered that all the tested fungi could paralyse and kill the worms within minutes of contact. Interestingly, the mechanism of paralysis was found to be conserved across nematode lineages that diverged between 280 and 430 million years ago. This suggests that the targeted mechanism is indispensable to the worms' survival.
The oyster mushroom's ability to paralyse and digest nematodes highlights the devious ingenuity and diversity of carnivorous fungi. While the mushrooms themselves are non-toxic and edible, their parasitic behaviour towards nematodes showcases the complex strategies employed by certain fungi to obtain nutrients from their environment.
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Nematodes are the most abundant animals in soil
Oyster mushrooms are carnivorous fungi that feed on nematodes, which are small, non-segmented worm-like animals. Nematodes are the most abundant animals in soil, accounting for about four-fifths of all animals on Earth. They are found in all types of environments, including soil, freshwater, marine environments, and even in unusual places like vinegar and beer malts. A single gram of soil can contain hundreds of nematodes. They are also present in astronomical numbers in the Earth's topsoil, with an estimated 4.4 x 10^20 nematodes, or roughly 60 billion nematodes for every human on the planet.
Nematodes play a crucial role in the terrestrial biosphere, influencing soil fertility and the exchange of gases with the atmosphere. They are important in controlling pest species and improving soil health. Beneficial nematodes feed on fungi, bacteria, and other soil organisms, while some predatory nematodes attack and kill pests such as borers, grubs, thrips, and beetles. They also help in the cycling of carbon and nutrients in the soil by breaking down organic matter and releasing excess nutrients in a form that plants can use directly.
The presence of nematodes in soil is influenced by factors such as soil characteristics and organic matter content. They are highly abundant in soil rich in organic matter and are commonly found in the top few centimetres of soil, where they require water to move. Nematodes have a diverse range of sizes, from microscopic to large parasitic forms found in whales that can reach up to 7 meters in length.
The study of nematodes is crucial for climate modelling and environmental decision-making. Their distribution patterns and interactions with other organisms, such as fungi, bacteria, and plants, provide valuable insights into the functioning of ecosystems and the potential impacts of agricultural practices on beneficial nematode populations.
In summary, nematodes are the most abundant animals in soil, playing vital roles in maintaining soil health and ecosystem functions. Their presence and activities have far-reaching implications for the natural world and human activities, including agriculture and environmental restoration projects.
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Carnivorous mushrooms are a biotechnological application
Oyster mushrooms, or Pleurotus ostreatus, are a type of carnivorous fungi. They were discovered to be meat-eaters in the 1980s when scientists found that they eat nematodes, or roundworms. Nematodes are tiny, but they are complete with guts, nerves, and muscles. When nematodes come into contact with oyster mushrooms, they are poisoned and paralyzed within minutes. The mushrooms then inject their filaments into the dead worms, dissolving their contents and absorbing the slurry.
Oyster mushrooms are not the only type of carnivorous fungi. In fact, about 200 species of fungi are known to attack, kill, and digest tiny animals, including protozoans, rotifers, and small arthropods. Some of the earliest evidence of carnivorous fungi was discovered in 100-million-year-old fossilized amber from southwestern France. This fungus, which lived during the time of dinosaurs, used constricting rings to trap its prey.
The discovery of carnivorous mushrooms has led to various biotechnological applications. For example, the spent mushroom compost of Flammulina velutipes has been found to exhibit nematicidal activity, which could be useful for organic agriculture. Additionally, the wood-degrading abilities of the genus Pleurotus have been studied for their potential applications. Furthermore, carnivorous mushrooms could be used as microbial control agents for fungus gnats, which affect the production of oyster mushrooms.
The study of carnivorous mushrooms and their unique abilities continues to provide valuable insights that can be applied in various fields, including agriculture and pest control. By understanding how these fungi interact with their prey and their environment, scientists can develop new biotechnological applications that can benefit society.
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Other fungi also eat nematodes
Oyster mushrooms are far from the only fungi that eat nematodes. In fact, there are over 700 species of carnivorous fungi that capture and eat nematodes, springtails, and amoebae. These fungi can be divided into four main groups according to the methods they use to catch their prey. Some use mechanical means, adhesives, or hyphal traps. Some produce toxins to immobilize their prey. Some are parasitic, using their spores to infect their prey, and some are egg parasites, inserting their hyphal tips into the eggs or cysts, or into females before the eggs are deposited.
One example of a nematode-eating fungus is Arthrobotrys oligospora, a net-building species that can detect the presence of nematodes in the soil and builds its snares accordingly. Another example is Arthrobotrys dactyloides, which employs a loop of hypha to catch nematodes. When a nematode tries to pass through the ring, the loop constricts rapidly, trapping the prey.
Nematophagous fungi are often found in nitrogen-deficient habitats and can be useful in controlling nematodes that eat crops. For example, Purpureocillium can be used as a bio-nematicide. Fungi that feed on nematodes have also been investigated for use in biological pest control.
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Frequently asked questions
Yes, some mushrooms are carnivores. Oyster mushrooms, for example, are known to feast on roundworms.
Carnivorous mushrooms poison and paralyze their prey within minutes of contact. They then inject their filaments into the corpses, dissolve the contents, and absorb the slurry.
Carnivorous mushrooms are known to eat tiny animals, including protozoans, rotifers, and small arthropods like tardigrades. Oyster mushrooms, in particular, eat nematodes, which are a type of roundworm.
Carnivorous mushrooms may eat meat to supplement the low levels of nitrogen available in their typical food sources, such as wood.
