Some of the most horrifying monsters are very small. The hungry flesh-eating fungus Arthrobotrys oligospora doesn’t look like much when it’s eating rotten wood. But when it senses a live worm nearby, it will grab its victim and consume it alive – pure nightmare fuel.
The Hungry Fungus
The fungus A. oligospora lives in the soil and is often considered a saprophyte, feeding on decaying organic matter. However, that can change quickly if it finds itself deprived of nutrients or senses the presence of an enticing worm nearby. In this case, it enters predatory mode.
Trap Formation
Lin and colleagues wanted to see what happens when the fungus, which is nutrient-starved, is introduced to the worm Caenorhabiditis elegans. The fungus showed a significant increase in DNA activity when it sensed the worm. This led to additional copies of the genome in trap cells. The trap cells are located in the fungal hyphae and produce a special adhesive that allows these parts to stick to the worm once it is caught in the trap.
Protein Production
Among the most critical genetic processes that help the fungus create a trap from hyphal parts is ribosome formation, which enables increased protein production. Ribosomes are where proteins are made, so their formation (literally creating more ribosomes) controls cell growth and also determines the quantity of synthesized protein.
Trap Proteins
A new set of proteins, now known as enriched trap proteins (TEPs), has also been identified as the most abundant proteins in the fungal trap cells. These proteins appear to contribute to the function of the trap rather than its formation.
“Given that TEPs are directed to the surface of trap cells, we hypothesized that TEPs could be crucial for trap function,” they stated in a study recently published in PLoS Biology. “Adding C. elegans… leads to their immediate capture.”
Aggressive Proteins
As the fungus exerts more effort to create a trap and form the worm adhesive, it reduces unrelated activities. Portions of DNA that usually help A. oligospora digest dead material are downregulated, meaning there is less genetic activity on these parts in response to the fungus’s detection of the worm. When the worm approaches A. oligospora, the fungus shows upregulation of genes that produce proteases, or enzymes that break down proteins.
No Way Out
No changes in the activity of other genes were observed until the worm was actually caught. Once C. elegans enters the trap set by A. oligospora with a sticky mesh of hyphal parts, the team noted an increase in the production of proteins that weaken the prey. These proteins can manipulate their host cells to act differently, providing a way for the fungus to infiltrate the cell and take control. The fungus then uses proteases to digest the entangled worms stuck in the hyphal parts of the trap.
Impact on Genes
A. oligospora has more than 400 genes encoding proteins that control its interactions with other organisms. When the introduction of the worm prompts the fungus to turn predatory, over half of these proteins began to behave differently. These proteins weaken C. elegans through a variety of mechanisms. For example, some combat antimicrobial peptides produced by the worm.
The adhesive produced by the fungus, which is now believed to be closely associated with TEP proteins, may not affect humans but is a strong adhesive for worms that binds the hyphal parts to their flesh. They have no way to escape once they are eaten alive.
May
This experience is horrific for the participating worms, but it was a breakthrough for the Lin team. They have now identified a whole new set of genes that make the fungus trap work. Their results can be compared to the gene activity of other pathogenic fungi, including those that destroy crops, so a future generation of antifungal treatments may one day be influenced by this microscopic horror.
References: PLOS Biology, 2023. DOI: 10.1371/journal.pbio.3002400
Source: Elizabeth Rayne – Ars Technica
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