Emma Wilson
Carnivorous mushrooms, or nematophagous fungi, are a fascinating subset of fungi that have been observed to attack, kill and digest tiny animals, including nematodes (roundworms). Oyster mushrooms, for example, poison and paralyze nematodes within minutes of contact, injecting their filaments into the corpses, dissolving their contents, and absorbing the slurry. This behaviour is thought to be a result of the low levels of nitrogen available in the mushrooms' typical habitats, such as wood. Other carnivorous fungi include species in the genera Trichoderma, Gliocladium, Hirsutella, Verticillium, Fusarium, Mucor, and some others. These fungi are characterized by the formation of special morphological structures that enable them to trap and digest their prey.
| Characteristics | Values |
|---|---|
| Types of carnivorous mushrooms | Oyster mushrooms, Flammulina velutipes, Trichoderma, Gliocladium, Hirsutella, Verticillium (= Pochonia), Fusarium, Mucor |
| Types of prey | Nematodes (roundworms), protozoans, rotifers, small arthropods (tardigrades, copepods, crustaceans), insects, spiders, other arthropods, small vertebrates (frogs, lizards, rats, birds) |
| How they catch prey | Poisoning, trapping mechanisms, attracting prey with nectar-like secretions, luring prey with chemical attractants |
| How they digest prey | Dissolving contents and absorbing slurry, digesting with enzymes and bacteria |
| Why they eat meat | Carnivorous mushrooms grow in habitats with limited nutrients, especially nitrogen, which is necessary for making proteins |
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What You'll Learn
Oyster mushrooms are carnivorous
Oyster mushrooms, or Pleurotus ostreatus, are carnivorous. They are among the most prized edible mushrooms collected in the wild. Oyster mushrooms grow on the trunks of dying and dead trees and break down the wood. The wood contains plenty of cellulose and lignin but little nitrogen, so these crafty fungi exude chemical lures to attract their microscopic prey, nematodes. Also called roundworms, nematodes are tiny animals complete with guts, nerves, muscles, and their own primitive form of hopes and dreams.
Oyster mushrooms poison and paralyze nematodes within minutes of contact, inject their filaments into the corpses, dissolve the contents, and absorb the slurry. This fungal poison probably irreversibly opens a calcium gate and/or jams the calcium pumps that re-stow it. Without a way of putting the calcium back where it belongs, the worm ends up in a rigor mortis that induces death. The poison produced by oyster mushrooms is so deadly that researchers have speculated it might be used to kill nematodes that attack crop plants.
Scientists have known for decades that oyster mushrooms feast on roundworms, but they have only recently discovered how their toxins work. In the 1980s, scientists discovered that oyster mushrooms are carnivores. A team of Taiwanese scientists sought to answer the question of how the fungal poison worked and published their results in the Proceedings of the National Academy of Sciences. They discovered that the fungus targets a part of the worms so indispensable that nematode species separated by more than 280 million years of evolution were equally susceptible.
Oyster mushrooms are far from alone among fungi in their eating habits, probably because nematodes are the most abundant animals in the soil. These little worms are so common that if the entire planet except nematodes were dissolved, a dimly visible Earth-shaped shell of nematodes would be left floating in space. This abundance of high-quality protein has spurred an outburst of fungal evolution.
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They poison and paralyse nematodes
Oyster mushrooms, or Pleurotus ostreatus, are a species of carnivorous fungi. They are known to prey on nematodes, which are tiny roundworms that are among the most abundant animals in the soil. Nematodes are a rich source of protein, which is a key nutrient that is often lacking in the habitats where these fungi grow.
Oyster mushrooms have evolved a unique strategy to capture and paralyze their nematode prey. They produce small lollipop-shaped structures called toxocysts on their fungal hyphae. These toxocysts contain a potent toxin, 3-octanone, which is a volatile ketone. When a nematode comes into contact with the toxocysts, the toxin is released, causing rapid paralysis and death.
The 3-octanone toxin disrupts the cell membrane integrity of the nematode, leading to a massive influx of calcium into the mitochondria and causing cell death. This process is similar to the mechanism of paralysis induced by snakebites and mass bee attacks. The dosage of 3-octanone is critical, with low doses repelling certain creatures and high doses proving lethal.
The Taiwanese scientists who studied the oyster mushroom's toxins discovered that the fungus targets a part of the nematode that is so indispensable that even nematode species separated by more than 280 million years of evolution were equally susceptible to the poison. This suggests that the mechanism of paralysis has been conserved by evolution across nematode lineages.
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Other carnivorous plants and fungi exist
Oyster mushrooms (Pleurotus ostreatus) are not the only carnivorous fungi. There are over 200 species of fungi that are known to attack, kill, and digest tiny animals, including protozoans, rotifers, small arthropods like tardigrades, copepods and other crustaceans, and nematodes (roundworms). Oyster mushrooms are just the only vegan food that can eat meat.
The oyster mushroom's method of killing its prey is particularly fascinating. It poisons and paralyzes nematodes within minutes of contact, injecting its filaments into the corpses, dissolving their insides, and absorbing the slurry. The poison works by irreversibly opening a calcium gate or jamming the calcium pumps that re-stow calcium in the worms' bodies. This causes neurons and muscle cells to die, leading to the worm's death.
Other carnivorous fungi include Trichoderma, Gliocladium, Hirsutella, Verticillium, Fusarium, Mucor, and some others. These fungi are traditionally known as antagonists, entomopathogenic, phytopathogenic, or typical saprophytic species.
In addition to carnivorous fungi, there are also many carnivorous plants. Over 600 species of plants kill animal prey, primarily insects, spiders, and other arthropods, but also small vertebrates, including frogs, lizards, rats, and birds. These plants often grow in habitats that offer few nutrients, especially nitrogen, which is necessary for making proteins. For example, the mountain treeshrew (Tupaia montana) feeds on the nectar of a carnivorous plant, perching directly over a funnel-shaped opening where it often defecates. The plant then digests the feces, providing itself with a rich source of nitrogen.
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Carnivorous fungi are used for biopesticides
Carnivorous fungi are commonly found in agricultural soils worldwide. They trap and eat microscopic nematodes (roundworms) that live in the soil and water. Nematodes are harmful to agriculture, significantly reducing the quality of vegetables and other crops. Classical pesticides are often ineffective or unsafe for human health and the environment. Therefore, biopesticides are preferable in green agriculture and pesticide-free food production.
The success of entomopathogenic fungi in nature has led to their development as biopesticides. Beauveria bassiana, for example, is antagonistic to plant pathogens, and Lecanicillium species are parasitic on fungal pathogens of plants. Several species of fungi, including Orbilia oligospora and Orbilia brochopaga, have shown high activity against the potato hookworm, demonstrating greater efficiency than commercial biopesticides. This may be due to the strain-specificity of nematicide enzymes in the observed fungi.
Fungal-based nematicides have been developed to reduce the number of phytopathogenic nematodes. In the second half of the 20th century, predatory fungi in the genera Arthrobotrys, Dactylella, and Dactylaria were identified as optimal for manufacturing microbial nematicides. More recently, interest has shifted to the nematopathogenic species Pochonia chlamidosporia and Purpureocillium lilacinus.
Mycoinsecticides, such as those based on the entomophthoralean fungus Conidiobolus obscures, are also used for pest control. However, a significant challenge with mycoinsecticides is long-term storage, as information on recommended storage times and expiration dates is scarce. B. bassiana, for instance, retains its activity after storage at 4 °C for 90 days, while M. anisopliae loses about 40% of its activity after six months of storage.
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Carnivorous fungi can be pathogenic
Carnivorous fungi are those that derive some or most of their nutrients from trapping and eating microscopic or other minute animals. They usually live in the soil and many species trap or stun nematodes (nematophagous fungi), while others attack amoebae or collembola.
Fungi that grow on the epidermis, hair, skin, nails, scales, or feathers of living or dead animals are considered dermatophytes rather than carnivores. Similarly, fungi in orifices and the digestive tract of animals are not carnivorous, and neither are internal pathogens. Insect pathogens that stun and colonize insects are also not typically labelled carnivorous if the fungal thallus is mainly in the insect or if it clings to the insect.
However, there is a group of fungi that are specifically pathogenic toward nematodes, the nematophagous fungi. Typical nematophagous fungi are carnivorous or predaceous and are characterized primarily by the formation of special morphological structures that enable them to trap and eat their prey. Oyster mushrooms, for example, poison and paralyze nematodes within minutes of contact, inject their filaments into the corpses, dissolve the contents, and absorb the slurry. They do this by irreversibly opening a calcium gate and/or jamming the calcium pumps that re-stow it, leading to the death of neurons and muscle cells.
Fungal pathogens of insects are dispersed as spores, which must land on the cuticle of an insect host and remain there until they can germinate. Different spore types have different adhesion properties and different cell wall surface carbohydrates, which affect pathogenesis as a result of differences in the insect immune system recognition.
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Frequently asked questions
Yes, there are carnivorous mushrooms. Oyster mushrooms, for example, are known to feast on nematodes (roundworms).
Carnivorous mushrooms have been found to poison and paralyze their prey. The fungal poison likely opens a calcium gate and/or jams the calcium pumps, leading to the death of neurons and muscle cells.
Carnivorous mushrooms grow in habitats with limited nutrients, especially nitrogen, which is essential for protein synthesis. By consuming prey, they can supplement the low levels of nitrogen available in their environment.
Aside from oyster mushrooms, other examples of carnivorous mushrooms include Flammulina velutipes and various species within the genus Pleurotus.
Yes, there are many other types of carnivorous fungi. Some examples include Trichoderma, Gliocladium, Hirsutella, Verticillium, Fusarium, and Mucor. These fungi are known to exhibit pathogenic behavior toward parasitic worms.
