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Oyster mushroom fungus uses nerve gas to paralyse and eat tiny worms

Oyster mushrooms are delicious, but they have a little-known dark side: the fungus that produces them paralyses and kills nematode worms using a nerve gas, before sucking out their insides.

Oyster mushrooms are the reproductive structures – or fruiting bodies – of the fungus Pleurotus ostreatus. We have known since the 1980s that this fungus preys on nematodes, which are microscopic roundworms, but how it does this has been a mystery.

Yen-Ping Hsueh at Academia Sinica, a research institute in Taiwan, and her colleagues previously discovered that P. ostreatus contains tiny, lollipop-shaped structures that break open when nematodes press their heads against them. They have now found that, once ruptured, these structures release a gas that is highly toxic to nematodes’ nervous systems.

The researchers determined this by first inducing thousands of random genetic mutations in the fungus, after which they noticed that mutants lacking these lollipop structures were no longer toxic to the nematode Caenorhabditis elegans.

Next, the researchers analysed the contents of the lollipop structures in non-mutant fungi and found that they were packed with a volatile chemical called 3-octanone. When they exposed four different nematode species to this chemical, it triggered a massive influx of calcium ions into nerve and muscle cells throughout their bodies, leading to rapid paralysis and death.

Hsueh calls this a “nerve gas in a lollipop” killing strategy.

The toxic lollipop structures are present on hyphae, the long, branching structures that grow inside rotting wood and make up most of the fungus. The oyster mushrooms themselves are non-toxic, says Hsueh.

After the fungus kills its prey, its hyphae grow into the nematodes’ bodies to suck out their contents. It may do this to absorb nitrogen, since this nutrient is deficient in the rotting wood on which the fungus mostly grows, says Hsueh.

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Nematodes are the most abundant animals in soil, which makes them a natural food choice for fungi, she says. Other fungi use different tactics to catch nematode prey, including sticky traps and nooses that tighten around their necks.

The finding that P. ostreatus feeds on nematodes has led to some discussion in the vegan community about whether oyster mushrooms are a truly vegan food.

Science Advances DOI: 10.1126/sciadv.ade4809

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