Figure 6. A model for trap formation by nematodes and bacteria.

When grazed by nematodes, bacteria increase the production and release of urea by upregulating the expression of arginase. Secreted urea is then taken up by the mycelia of nematode-trapping fungi nearby via a urea transporter, and eventually catabolized to ammonia by urease within the fungi. Ammonia in turn initiates the lifestyle switch to form trap structures. Meanwhile, ascarosides released by nematodes are transported into the mycelia of nematode-trapping fungi by unknown proteins, and induce trap formation directly. The bacteria/urea- and the nematode/ascaroside-mediated signalling pathways exhibit significant synergistic effects on trap formation, resulting in the eventual capture and death of the nematodes.