Carnivorous Mushrooms?

Many different fungi are known to have antibacterial properties. Recent research has shown that some fungi also hunt and kill larger organisms, including nematodes. These worm-like creatures are amazingly abundant in the soil, in plants, and even other animals. Some have speculated that if all other (non-nematode) matter were to disappear, a ghostly outline of the world would remain, made of writhing nematodes. Some fungi have evolved structures to trap these creatures, including chemically-"sticky" knobs, snare-like loops, and predatory hyphae (fungal threads). It's thought that the nematophagous (nematode-eating) fungi attack their prey as a source of nitrogen, a precious, limiting nutrient in their environment. This video (by T. Loynachan of Iowa State University) shows some of these traps in action in unidentified soil fungi.

Oyster mushrooms (Pleurotus ostreatus) offer a dramatic example of nematophagous behavior, even though they are technically saprobes (dining primarily on dead or dying wood cellulose). The image below shows a nematode that has been paralyzed by the nematotoxin ostreatin, which is produced special structures on the hyphae of oyster mushrooms. Utilizing chemical signals, the hyphae of the fungus have located the mouth of the nematode, and have grown into its body to digest it.
The same kind of predatory hyphae seek out bacterial colonies, drawn by their chemical signatures. The fungal threads will penetrate a bacterial cluster at several points simultaneously, as seen in the image below. The fungus then dissolves and digests the bacteria. This type of behavior may have originally evolved for self-protection, but it clearly benefits the fungus nutritionally to consume its little guests. So, when you eat oyster mushrooms, you are eating higher on the food chain than you thought!