Chemical Carnivory in Pleurotus: Induced Toxin Droplets Contain 3-Octanone and Candidate Nematicides

Predatory oyster mushrooms (Pleurotus spp.) immobilize nematode prey using toxin droplets. The chemical composition and regulation of toxin droplet production have remained incompletely characterized since their initial observation over 40 years ago, though 3-octanone has been identified as a possible contributor. We quantified toxin droplet abundance in twenty Pleurotus strains spanning six species and compared their chemical profiles using GC-MS headspace and liquid sampling. Droplet abundance varied among strains and, in most, increased following the addition of washed nematodes. Strains that produced many toxin droplets had distinct volatile and liquid metabolite profiles compared with low-droplet-producing strains and control groups. Our targeted analysis identified 3-octanone in seven Pleurotus strains, including its first reported detection in P. eryngii and P. populinus. Our untargeted analysis putatively identified several additional candidate nematicidal molecules that were significantly enriched in high-droplet producing strains. Here, we provide evidence consistent with the hypothesis that Pleurotus may use a cocktail of secondary metabolites, rather than 3-octanone alone, to paralyze nematode prey, supporting an alternative to the one-molecule mechanism of paralysis.