Split Personality

Behold, the Arthrobotrys oligospora. It's a seemingly innocuous fungus that has long fascinated biologists for one of its cute characteristics: doubling as a bloodthirsty, systematic killer of innocent worms.

A new study published in the journal PLOS Biology explores the fascinating mechanisms that this so-called nematode trapping fungus uses to hunt its prey — a wonderful example of all the cool and kind of messed up tricks that nature's tiny creatures use to annihilate each other.

A. oligospora are usually bog standard decomposers, feeding on dead organic matter. But tough times and scarce food can drive them to drop the nice guy act and absolutely decimate whatever wriggling, helpless worms cross their path — preferably nematodes, as their common name suggests.

While this fascinating fungal carnivore mode has been studied before, the researchers here wanted to dive into what's causing it at the molecular level.

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Much like carnivorous plants such as the venus flytrap, the fungi is crafty in its hunting, forming traps of its own to lure and capture their prey. The traps, which the researchers called "adhesives nets," contain a gooey substance made of trap enriched proteins (TEP) that make it difficult for worms to escape, no matter how hard they might writhe and wriggle.

Once immobilized, the fungi descend on their prey. They "eat" it by invading it. Fungal filaments called hyphae — typically feathery and branchy, and when found in large patches called mycelium — pervade the worm inside and out. And voila: the worm is now, in a tragi-comic reversal of the term, worm food.

So what's underlying this carnivorous streak? Using a genetic analysis technique called RNA sequencing, the researchers found that an A. oligospora's DNA replication and ribosome production goes into overdrive when it detects a worm. Essentially, this gets the fungi amped up to kill.

But what really kicks into gear are genes that encode for the secretion of the TEPs. As it turns out, these are crucial for efficient hunting. The researchers found that when these TEP genes are turned off, the fungi — now unable to secrete the oozy substance — were significantly less successful at trapping nematodes.

As for just how the hyphae digests its game, the researchers found increased activity in the genes that release what's known as proteases, a type of enzyme that breaks down and digests proteins and peptides.

All told, if you're fascinated by the brutal side of nature, don't overlook these fungi. It's a merciless world down there.

More on fungi: Fungus Learns to Infect Human, Spreading "Root-Like Filaments"

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