Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Thorn, Greg R.

Abstract

Pleurotus—known as oyster mushrooms—are nematophagous fungi that utilize secondary metabolites to paralyze nematode prey. When grown in nutrient poor environments, members of Pleurotus produce liquid, nematotoxic secondary metabolite containing microdroplets from spathulate secretory cells. Although toxin droplet-nematode interactions have been well documented in the literature, little is known of the regulation of toxin droplet production in response to external stimuli. Moreover, the identity of the bioactive secondary metabolites contained within the droplets of Pleurotus remain unconfirmed. This study is the first to confirm that the presence of nematodes influences the abundance of toxin droplets produced by Pleurotus and characterizes the total metabolic profile of Pleurotus toxin droplets. The data presented in this study also identifies several metabolites with nematicidal potential that may be considered as candidate nematicides for the control of nematode pests.

Summary for Lay Audience

Pleurotus, commonly called the oyster mushroom, is a type of fungus that produces edible fruiting bodies. It is the third most cultivated mushroom worldwide. Although considered a popular edible mushroom enjoyed in global cuisines, the oyster mushroom is also valued for its medicinal properties as it is the source of bioactive molecules that benefit human health.

In nature, Pleurotus usually grows as a network of tiny threads called hyphae. These hyphae grow through soil and rotting wood. As these environments are often low in nutrients, Pleurotus uses a strategy to supplement its diet by consuming microscopic worms from the phylum Nematoda, called nematodes. The fungus produces tiny droplets along its hyphae that contain chemicals that are toxic to nematodes. When a nematode touches a droplet, the droplet bursts, releasing toxins that paralyze the worm. This gives the hyphae time to grow toward the nematode, invade its body, and consume it.

Many studies have found toxin droplets in different Pleurotus species. However, little is known about the the factors that may influence their abundance. In this study, I looked at how many droplets appear when nematodes are present versus when they are absent. I found that more droplets are produced when nematodes are present.

Researchers have tried to identify which molecules in the droplets cause paralysis. Some studies could not isolate the active molecules, while others only looked at parts of the droplets. In my research, I studied both the liquid and gas components of the droplets. I identified several molecules that are confirmed to paralyze nematodes and several other molecules that are suspected to paralyze nematodes. However, additional studies need to be conducted to confirm if these untested molecules cause nematode paralysis.

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