Unlike most other mycotoxins found in food, the ochratoxins are primarily produced during food storage. Fungi in the genera Aspergillus and Penicillium are common molds that decompose a variety of foods, from grains to coffee to grapes. In the process, many of those fungi produce ochratoxins, which can damage the kidneys and cause cancer in many animals. Ochratoxins presumably impact humans the same way, but researchers have so far been unable to directly link ochratoxins to any human disease. This is probably because human consumption of ochratoxins is usually very low.
Fungus Fact Friday
Zearalenone is a fascinating mycotoxin produced by Fusarium species. It is the only mycotoxin that mimics the effects of the hormone estrogen. In high doses, it causes sexual organs to develop incorrectly. Pigs are the most susceptible animals and suffer estrogenism and vulvovaginitis when exposed to high levels of zearalenone. The toxin is present in many grain-based foods intended for human consumption, but usually at very low levels. As a result, zearalenone is generally harmless to humans.
Humans have very little to worry about from fumonisins, mycotoxins produced by Fusarium fungi that cause Fusarium ear rot disease of corn (maize). The toxins are linked with esophageal cancer, but scientists cannot prove that they cause cancer. However, fumonisins are a major problem for horses and pigs. In horses, the toxins cause liquefaction of the brain tissue, while in pigs they cause the lungs to fill with water.
In honor of the recent Thanksgiving holiday, I chose to rework this post on the Turkey Tail. I will continue discussing mycotoxins next week. It is easy to see why Trametes versicolor is commonly called the “Turkey Tail”: the upper surface of the fan-shaped polypore sports rings of color that vary from gray to brown to reddish-orange. In fresh specimens, the edge of the mushroom is white, making it look remarkably like the displayed tail of a wild turkey. T. versicolor is a very common decomposer and produces mushrooms that are visible all year, so you can probably find it the next time you walk through the woods.
Deoxynivalenol (DON) is a toxin found in grains infected with the fungus Fusarium graminearum and other Fusarium species. It is often called “vomitoxin” because it primarily causes vomiting in humans and livestock. Its long-term effects are mild, but it is still a very important mycotoxin because it is the most common mycotoxin found in food.
Fungi produce innumerable “mycotoxins” – compounds that are toxic to humans. In mushrooms, these cause symptoms ranging from gastrointestinal upset to death (see FFF#091–100 for more). Although these are of significant concern to mushroom hunters, their impact is relatively small. The most significant mycotoxins in terms of the number of people affected are produced by molds that naturally grow on food. Over the next few weeks, I will discuss some of the most problematic food-borne mycotoxins. Topping that list are the aflatoxins, which cause liver cancer and are especially problematic for people in developing nations.
Fungi appear in the news with surprising frequency. However, many of those stories do not provide any new information. Below is a summary of what we’ve learned about fungi from August through October 2017. Read below to learn about: ballistospory, chromosome evolution, fighting fungal pathogens (in humans, bats, and bananas), psilocybin, oil-eating fungi, and more! Visit the associated links to get the full story.
If the spirit of Halloween were a mushroom, it would be Omphalotus illudens. This agaric is commonly known as the “Jack-O-Lantern mushroom” for a few good reasons. First, it is bright orange, like the pumpkins that decorate doorsteps all over the United States in October. Not only is the cap orange, but so are the gills, the stipe, and the interior. Second, the mushroom’s gills glow in the dark, especially when they are young and fresh. Furthermore, the mushroom often has a sweet smell and is poisonous. Nothing says Halloween like something that is orange, glows in the dark, smells sweet, and has a sinister side.
In late October, it is not unusual to see Halloween decorations featuring bony fingers reaching up out of a grave. The natural world has its own version of this: Xylaria polymorpha, commonly known as Dead Man’s Fingers. This macabre name is an apt description of the mushrooms, which resemble burnt and dried out fingers reaching out of the ground to grab unwitting passers-by and drag them down into the depths of the earth. You can find these morbid ascomycetes on rotting logs at pretty much any time of the year.
One day as you check your mailbox you notice a yellow smear on the entrance to your house (for example a wooden gate). After retrieving your mail, you take a closer look and see that it’s a yellow gelatinous lobed blob – Witch’s Butter! Oh no, you think, I’ve been hexed by a witch! Knowing just what to do, you run back to the house, collect a few straight pins, and stab them through the offending substance to drain its juices and kill the spell. Unfortunately, this method doesn’t work very well for two reasons. First, this blob is actually the jelly fungus Tremella mesenterica. Like all jelly fungi, it is specifically designed to survive repeated dehydration and rehydration. Second, the main body of the fungus is still living inside the wood; unless you replace the wood, the mushroom will probably reappear in the same place!
Welcome back to creepy fungus month! I’m starting off this month with a mushroom that has a creepy name but is always fun to find: The Witch’s Hat. Hygrocybe conica gets its common name from the conic shape of its cap, its orange to red color, and its tendency to bruise strongly black. Actually, this last feature is probably the most important; when the mushrooms turn completely black they really do look like tiny hats for witches! The Witch’s Hat grows on the ground in a variety of habitats and mycologists are not sure what its ecological role is.