Meet the worm-eating fungus that goes full-on carnivore when food is scarce

Like plants and animals, fungi require nutrients to live – usually obtained from their surrounding environment – but sometimes starvation forces them to look for alternative meals.

Arthrobotrys oligospora is a unique ascomycete or sac fungi species, a division of the kingdom that includes the antibiotic-producing Penicillium chrysogenum, baker’s yeast, and truffles, as well as many others that are disease-causing in plants and animals.

A. oligospora is a useful pest-controller. It lives in soil where it usually has a saprotrophic diet, obtaining its nutrition by feeding on chemicals from decaying organic matter.

But when chemicals from dead plants aren’t available, it embraces a more flexitarian approach to eating, targeting nematodes – worms – instead.

These hangry fungi can’t chase after their prey though, and rather than relying on these other wriggly soil-dwellers to worm their way into a fungal trap, A. oligospora have evolved a series of processes to lure them in.

Studying the behaviour of A. oligospora’s genes while it ‘hunted’ a Caenorhabditis elegans worm in the lab, researchers from Taiwan uncovered very specific stages of predation.

It was already known that the fungi mimic the food and sex signals that worms rely on during their lifecycle, by releasing pheromones that attract female and hermaphroditic nematodes into their vicinity. A series of genes then perform a range of tasks in forming trap-like structures to snare the worms.

Now, the researchers have filled in the blanks of these steps. Once a worm is sensed, A. oligospora creates ribosomes which produce specialised proteins, which are then used to create the ‘traps.’  These include ‘worm adhesive’ proteins that help with prey capture.

When trapped, the fungus sticks its long, filament-like hyphae into the worm and other genes create enzymes that break down proteins.

This, they suggest, helps make the worms far easier for the A. oligospora to digest.

“We have identified that upon nematode exposure, A. oligospora first up-regulates ribosome biosynthesis and DNA replication,” the authors write. “This work lays a solid foundation for future investigation of the molecular mechanisms underlying predator-prey interactions between nematode-trapping fungi and nematodes and allows parallel comparison with other pathogenic fungi and their interactions with plant or animal hosts.