Scientists at VIB and Vrije Universiteit Brussel in Brussels have discovered why a widely used natural pesticide works so well—and the answer is invisibly small: protein fibers just eight nanometers wide that form a molecular net called "sporesilk."
The finding matters because agriculture worldwide is searching for alternatives to chemical pesticides, and Bacillus thuringiensis (Bt) is already trusted and widely deployed. It's a bacterium that targets only certain insect larvae, leaving humans, other wildlife, and beneficial insects like bees unharmed. But until now, researchers didn't fully understand how Bt's lethal two-part system actually stayed together long enough in the environment to infect insects effectively. The bacterium releases toxins that breach an insect's digestive system, then sends in spores to germinate and multiply inside the larva. When the food source is depleted, new spores and toxins are released, ready to infect another host. The puzzle was: what kept these spores and toxins together?
The answer emerged from advanced imaging techniques used by Prof. Han Remaut's team at the VIB-VUB Center for Structural Biology. They discovered that Bt spores and toxin crystals are embedded in a dense mesh of ultra-strong protein fibers that assemble themselves into a double-helical structure and are chemically crosslinked into an exceptionally stable material. "This is one of the most robust protein materials we've seen in nature," Remaut explains. These fibers remain intact under extreme conditions—heat, drought, harsh chemicals, and mechanical stress—forming what the team calls sporesilk.
Dr. Mike Sleutel, also from VIB-VUB, describes the mechanism: "The sporesilk acts as a molecular net that clusters the spores and toxin crystals into compact 'infection units,' so when insect larvae ingest the bacteria, they receive both the infectious spores and the toxic payload at the same time." The researchers proved this by removing the gene responsible for producing these fibers. The clusters fell apart, and the bacteria became significantly less effective, with delayed mortality observed in experimental models. When they added the fibers back—either through genetic engineering or by mixing in purified fibers—spore–toxin clustering was restored and insect-killing efficiency increased substantially.
The implications are immediate and practical. "This could offer a way to develop more potent and reliable biopesticides while maintaining regulatory and environmental safety standards," Remaut says. The discovery, published in Nature Communications, opens a door to engineering stronger, more stable formulations without compromising the safety profile that has made Bt a trusted tool in organic and conventional agriculture alike.
Beyond biopesticides, the extreme durability and self-assembling properties of sporesilk hint at broader applications. These protein fibers could inspire new biomaterials for biotechnology and engineering. As the world reckons with the environmental costs of chemical pesticides, understanding and harnessing natural systems already perfected by evolution could prove essential—not just for protecting crops, but for building a more sustainable agriculture.