The Egh16-like virulence factor TrsA of the nematode-trapping fungus Arthrobotrys flagrans facilitates intrusion into its host Caenorhabditis elegans.

The first physical barrier pathogenic microbes need to overcome for host colonization is the cuticle, epidermis, or skin of an animal. The nematode-trapping fungus Arthrobotrys flagrans is able to catch and digest nematodes like Caenorhabditis elegans by overcoming this physical barrier of the nematode and colonize the entire body. Here we characterized TrsA (trap-specific protein), a virulence factor of A. flagrans that is produced in the adhesive traps of the fungus and in trophic hyphae. Deletion of trsA increased the time until the fungus entered the nematode. Heterologous expression of trsA in C. elegans shortened its lifespan and led to softening of the animal. The protein structure of TrsA displays some characteristics of lytic polysaccharide monooxygenases (LPMOs), and TrsA indeed showed copper-dependent oxidase activity. LPMOs are enzymes with roles in the degradation of polysaccharides such as chitin and cellulose but also in organismic interactions and can be found in bacteria, fungi, plants, and insects. We hypothesize that TrsA defines a new LPMO family that likely targets oligosaccharides in the cuticle and the extracellular matrix of C. elegans and thereby facilitates entry into C. elegans and spreading of the fungus in the nematode body.