video: Utilizing the OEDhgh1::mCherry transformant with fluorescently labeled virulensomes to investigate the infection process of Dactylellina haptotyla on nematodes, live-cell imaging captured adhesive knobs adhering to the nematode head and forming infection bulb. Subsequent time-lapse imaging revealed that the labeled virulensomes gradually entered the nematode body over time. HIS-SIM captured images at 5-second intervals over a total duration of 90 minutes.
Credit: ©Science China Press
Unlike mobile animals, fungi are generally unable to actively escape from or pursue their opponents. For nematode-trapping fungi that encounter mobile nematodes in their environment, survival depends on developing effective strategies to detect, capture, and overcome these mobile hosts. Over the course of evolution, these fungi have developed a variety mechanisms, including specialized trapping structures and potent virulence factors, to efficiently attack and utilize nematodes as a nutrient source.
In this study, researchers discovered a novel infection-associated organelle, named the “virulensome,” in the nematode-trapping fungus Dactylellina haptotyla. The virulensome is a membrane-bound structure approximately 100–250 nm in size and forms rapidly when the fungus detects nearby nematodes. These specialized organelles act as cellular “attack platforms” that concentrate a large number of virulence-related proteins, including enzymes capable of degrading nematode tissues.
During the infection process, virulensomes are transported to the contact site between the fungus and the nematode, where they release their cargo to facilitate host tissue breakdown and promote fungal invasion. Purified virulensomes alone were sufficient to cause severe damage to nematodes, demonstrating their direct role in fungal predation. These findings suggest that, rather than relying on individual virulence factors acting independently, fungi can pre-organise a coordinated intracellular infection system.
The discovery of virulensomes provides a new perspective on how pathogens organize and deploy their infection machinery at the subcellular level. Although they were first identified in D. haptotyla, similar vesicle structures have since been observed in other fungal infection systems. This suggests that the compartmentalized delivery of virulence factors may be a more widespread strategy employed by microbes during host invasion.
Journal
Science China Life Sciences
Method of Research
Experimental study