Mycophilia, p.10
Mycophilia, page 10
There are two types of cheeses that benefit from saprophytic mold. Blue cheeses like Gorgonzola and Roquefort utilize Penicillium roqueforti. The curd is inoculated with the mold, which then grows throughout the cheese, adding flavor and fragrance. Camembert and brie-type cheeses are ripened with P. camemberti. The mold creates the thick white rind and digests the milk proteins—that’s what creates the silky mouthfeel.
But above all, saprophytic fungi degrade the plant fibers cellulose and lignin, and in the process enrich soils. Indeed, fungi are the digestive organs of forests.* In the wild, it is the wood-decaying fungus’s job to break down cellulose and lignin. Cellulose is the primary structural component of the cell walls of green plants, comprising almost half of the dry wood weight, followed by lignin, which adds structural stability to the cell walls, mostly in woody perennials like trees. Lignin sequesters carbon and is very slow to decompose. Some wood-decaying fungi degrade lignin first, and then later will go after the cellulose and other parts of the wood cell, while others degrade just cellulose and don’t even go for the lignin.
Saprophytic fungi can cause all kinds of damage, but if it weren’t for the wood decayers and their ability to break down organic debris, we would be buried under miles of dead plants. The fact that during the Carboniferous period massive amounts of dead plants did accrue (and turned into the fossil fuels) suggests there may have been a lack of lignin-eating fungi at that time. “We speculate that fungi that degrade cellulose evolved first because cellulose is a simpler compound to degrade,” said Tom Volk. “A period—a long period—passed before fungi evolved to degrade lignin, too, and all the while plants were protecting their cellulose with lignin. So, during the time after the introduction of fungi that decay cellulose, but before the introduction of fungi that can decay cellulose and lignin, only parts of plants rotted. The parts that did not rot became compressed into fuels. That’s not going to happen again.”
Oyster mushrooms fruiting along the baseboard of a home
The dark side of all this wood eating is the destruction of wood products that we would rather fungi stay away from. Dry rot, which probably got its name for the crumbly texture of wood in an advanced state of decomposition, was a huge nuisance for the navy prior to the development of ironclad ships in the late 19th century. “But don’t blame the fungi,” said Volk. “They don’t know it’s not a tree.” There are regular reports in regional newspapers about oyster mushrooms fruiting along the baseboard of homes, dock pilings decomposing, library books turning moldy. If you kept them around long enough, your dollars would decay (they are covered in mold spore). You’ve likely seen the paper sheath of Sheetrock walls stained with blotches of mold. Anything made from wood and exposed to water is an all-you-can-eat buffet for saprophytic fungi.
Two notable molds famous for the trouble they cause to property and food products while in storage are Stachybotrys and Aspergillus. Stachybotrys, known as “black mold,” is the mold you see in pictures of postflood homes where big black blooms of the stuff cover interior walls like ominous polka dots. It can produce trichothecenes, a family of mycotoxins that can be harmful to humans and animals. Aspergillus is a genus composed of several hundred mold species, at least one of which produces the carcinogenic toxin, aflatoxin.
Except in rare cases, such as a farmer handling large amounts of contaminated grain in a closed environment like a silo, molds need to be either weaponized or swallowed (or inhaled in some cases) to cause serious health effects in animals or people. Molds do not produce these toxins to harm animals. Instead, mycologists think these toxins are produced to battle rival microbes, like other fungi, bacteria, and soil protozoa, for food. Animals and people just sometimes get in the way.
The third category of fungi are parasites. Parasites depend on living hosts for their survival, and a parasite that is consistently related to disease is called a pathogen. Pathogenic fungi affect humans in many ways. They are a scourge on human health, crops, and trees; they cause billions of dollars in damage worldwide—85 percent of all plant diseases are caused by fungi—and are responsible for countless famines recorded from Biblical times through today. Like an infectious agent, pathogenic fungi often kill their living hosts—animals, plants, and other fungi—or inhibit their ability to reproduce. Most are microfungi that, like other predators, do the job of natural selection, singling out the weakest organisms for destruction. The lobster mushroom (Hypomyces lactifluorum) is an example of fungus-to-fungus pathogenicity. An edible fungus parasitizes another fungus, usually either an edible Russula or an (otherwise) inedible Lactarius, deforming the host’s cap, stem, and gills, and turning the fungus a bright orange. The lobster mushroom is delicious, but it can’t reproduce.
Evidence of pathogenic fungi was everywhere at the NAMA foray in Colorado. The forests around Winter Park, once dark green and glorious, are now dead, devastated by a lethal infestation of fungi and its insect vector. It did not look mushroomy at all. But people were hunting mushrooms nonetheless.
I was, too. I took off with Larry Evans, who was selling his wild mushrooms in the vendors area, up into the crispy mountains. Larry is well known on the mushroom scene. He is tall and lanky and wears his hair in gray braids. When I met him, he was eating a raw porcini mushroom like an apple. He told me he eats mushrooms every day, often raw, so I imagine his digestive system is a bit like a bobsled track. When I got into his red Subaru, I noticed he’d decorated it with white refrigerator magnets so that it looked like an Amanita muscaria, and as Larry sped along, his exhaust pipe scraping the rutted dirt roads, the magnets kept flying off the hood and whizzing by my passenger window. Up, up, up we went, 10,000 feet high to look for hunting grounds with healthy trees. Larry pulled over at a spot that was so steep I had to go up on my knees and down on my bottom. But he was unfazed, and sang as he climbed from his CD, Fungal Boogieman, which features songs like “Breakfast of Champignons” and “Everything’s Got a Fungus.” Unfortunately, even at this altitude, the forests were dead: a dry reddish brown that seemed just a pack of matches away from an inferno.
Old growth chestnut, Great Smoky Mountains, NG (ca. 1910)
Most of the plant pathogens we see every day are those that attack trees. Here in the United States we’ve lost, and continue to lose, vast forests to fungal pathogens. Mountain pine bark beetles in cahoots with fungi killed the forests surrounding the Snow Mountain Ranch, and so far around 3 million acres of Colorado pine forests have been affected. The mountain pine bark beetle is spreading the blue stain fungus, Grosmannia clavigera, among pine trees—mainly ponderosa and lodgepole. The fungus interrupts the tree’s ability to conduct water and stains the wood blue. Some people choose this wood for furniture, calling it “blue pine.” The American chestnut used to be known as the Redwood of the East, with trees reaching a circumference of up to 10 feet and a height of 120 feet—higher than a 12-story building. Chestnut trees ranged over 200 million acres of eastern woodlands from Maine to Florida until the chestnut blight Cryphonectria parasitica wiped out 3 billion trees in the first 50 years of the 1900s by rotting the cambium, the critical layer of living cells just under the bark that generates new wood. The fungus was spread by woodpeckers. Dutch elm disease, caused by a few species of fungi from the Ophiostoma genus, has had a similar devastating effect on the American elm tree (as well as the European elm). So far, 100 million trees have died in the Northern Hemisphere since the epidemic began around 1918. It arrived in the United States via infected elm burl logs that were imported for furniture manufacture. The fungus, transported by various species of bark beetles, attacks the tree’s vascular system and renders it incapable of conducting water.
Those are the big die-offs. But in any given year, newspapers will publish stories about local threats to native species—dogwoods, oaks, beech trees, white pines—where trees stressed by drought or other environmental factors become vulnerable to fungi and their insect vectors.
Pathogenic fungi of crop plants are a major cause of famine worldwide and the single most important cause of plant disease. There are pathogenic fungi that grow hyphae, like the Fusarium genera. Species in this group are responsible for scab, a particularly devastating disease of wheat and barley, and the “H.I.V. of banana plantations” according to an Australian newspaper.* Fusarium also attacks chile seeds. In fact, the chile pepper produces its delicious heat as a strategy to repel the fungus.
Then there are the many smuts and rusts and molds that cause tremendous damage to a wide variety of crops, from grains to grapes, chocolate to corn, rubber (the nonsynthetic kind used to make, among other things, condoms) to rice, and they have been wreaking havoc as long as humans have farmed. The Federal Plant Quarantine Act of 1912, which has been amended many times, most recently in 1994, seeks to control the importation of plant pathogens. Unfortunately, it’s hard to manage a microfungus.
Corn smut causes fungal tumors on the ears of corn that taste delicious.
Smuts—and there are about 1,200 described species—tend to replace the fruits in a plant, interfering with its ability to reproduce, causing the plant to grow galls or tumors, and costing millions of dollars a year in damage, mainly to cereal crops. But one man’s tumors are sometimes another man’s treasure. The corn smut Ustilago maydis, which causes fungal tumors on the ears of corn, is known in Mexico as huitlacoche or cuitlacoche, maize mushrooms, or Mexican truffle. The immature galls have been considered a delicacy since pre-Columbian times. It tastes delightful, of both mushrooms and corn, and is rather exotic, like a vegetarian foie gras. Four hundred to 500 tons of huitlacoche are sold annually in Mexico, and a few US farmers have gotten into the business as well, but while the fungus can be more profitable than the corn it grows on, marketing a product called smut has its challenges.
Rusts are so called because a leaf sprinkled with their reddish spores or small brown pustules looks like rust. They are pathogens of foliage, killing leaves and debilitating the plant. There are about 5,000 species of rusts and, like smuts, they can have a devastating economic impact. Rusts have plagued crops since the dawn of agriculture. The Romans conducted an agricultural festival on April 25, the Robigalia, where red-haired dogs were sacrificed in order to appease the personification of rust disease, Robigus. Of the many famines caused by rust, the most well known may be the Egyptian famine described in Genesis in the Old Testament (the one Joseph alleviated on behalf of the Pharaoh). Currently, a rust named Ug99—for where (Uganda) and when (1999) it was first identified—has already jumped the Red Sea and entered the wheat fields of Iran. It now seems poised to enter India. The worst rust outbreaks have been controlled for many decades through the development of rust-resistant wheat seed,* but 90 percent of the world’s wheat has little or no resistance to this strain. Researchers are currently racing to develop a Ug99-resistant wheat ahead of the pathogen’s migration.
Molds cause enormous crop losses as well. While some species of the Aspergillus genera are saprophytic in lifestyle—they feed on cereals that have already been harvested—others infect living cereals, spices, nuts, and cotton and can also produce dangerous mycotoxins, contaminating foods that can cause poisoning in the people and animals that consume them. For this reason, the USDA monitors peanuts and field corn for “unacceptable levels” of aflatoxin.
One of the most famous crop pathogens is Phytophthora infestans, which decimated Irish potato crops over a 5-year period in the 1840s. The potato was the staple food for one-third of the population; when the crops failed, approximately 1 million people either starved to death in the countryside or moved to cities in search of food, where they died of epidemics like typhoid, cholera, and dysentery. Another million emigrated to England, Australia, and the United States. Potato blight, which turns the tubers into stinky black slime, was long thought to be a mold. In the past 30 years, P. infestans has been reclassified a few times, and though it is still studied by mycologists, currently P. infestans is a member of a weird kingdom called Stramenopila, which some consider the sixth kingdom, home of organisms like giant kelps.
Farmers don’t despise all molds, though: The noble rot, Botrytis cinerea, is a pathogenic mold that attacks fruit and consumes their water. It is bad news for strawberries, but if it infects the wine grape during wet conditions and if the weather then dries up, the resultant raisiny grapes produce some of the best wines in the world, including the Hungarian Tokaji Aszú, French Sauternes, German Eiswein, and Italian Amarone.
Many fungi are parasites of animals, keeping populations in check and ecosystems in balance. All kinds of animals, from nematodes (1⁄32-inch-long soil-dwelling eelworms) to humans, dogs and cats to oysters and sponges, fall prey to pathogenic fungi. Some fungi, given the right conditions, even threaten their host species with extinction. Fusarium solani is suspected of playing a key role in the decline of the loggerhead sea turtle. A virus and a member of the microspordia, a fungal parasite of animals, working together, may be behind the colony collapse disorder currently decimating the honeybee population. A chytrid fungus (belonging to a primitive division of the kingdom fungi) poses one of the biggest threats facing the amphibian species today, having hitched a ride on certain species of African frogs that were exported for use in pregnancy tests. The disease caused by the fungus, chytridiomycosis, is responsible for the decline or extinction of up to 200 species of frogs worldwide, and, according to the biologist Lee Francis Skerratt, “the most spectacular loss of vertebrate biodiversity due to disease in recorded history.”
Bats infected with white-nose syndrome
The bat story is similar. Bats across the eastern United States are dying due to a new fungus infection called white-nose syndrome (WNS). It has spread into at least a dozen states east of the Mississippi and killed more than a million bats to date. Researchers have estimated that North America’s most common bat will be virtually extinct by 2026. The fungus, which is cold tolerant, grows on the bats’ muzzles, wing membranes, and ears while they are hibernating, causing the bats to waste away, then wake up early from hibernation to forage in weather that is too cold for them.
Gordyceps sinensis, a parasite of the larva of the ghost moth
Manipulating host behavior is definitely a survival adaptation for some parasitic fungi. For example, one species of Cordyceps attacks bullet ants. Hyphae infiltrate their bodies and their brains. The fungus infection induces a kind of mind control, because the ant is compelled to climb high into the foliage and then grip a stem with its mandibles, where it dies. If a member of the ant colony finds an ant infected with Cordyceps, it is removed far away from the colony. But if not, a fruiting body (it’s not exactly a mushroom) erupts from the ant’s head, growing like a slender worm as long as the ant itself, its tip packed with spores, which it sprinkles on the ants below.
The name Cordyceps refers to the morphology of the mushroom (from the Latin, cord = club and ceps = head), and they can look like miniature rubbery billy clubs. There are about 400 described species, most of which are exclusive to one or just a few hosts. The most famous is Cordyceps sinensis (from the Latin, sinensis = of China), a parasite of the caterpillar of the ghost moth. The infected caterpillar hibernates underground during the winter, and in early summer the fungus compels the caterpillar to crawl close to the soil surface. The fungus absorbs all of the worm’s nutrients, replacing the insides of the caterpillar with mycelium, and a club-shaped fruiting body grows out of the insect’s head and pushes up through the soil. The mycelium-riddled caterpillar carcass and the mushroom that erupts from its head have an ancient reputation as a cure for a number of ailments in traditional Tibetan and Chinese medicine.
Daniel Winkler is probably the leading expert when it comes to the ethnomycology and economy of the C. sinensis harvest in Tibet. Winkler is a long-haired, excitable German who first came to the USA to follow the Grateful Dead but who now makes a living being an expert on this particular fungus—no small task. According to Winkler’s research, the appearance of C. sinensis, also known as the caterpillar fungus, sets off a regional harvesting rush that occupies up to 60 percent of the population in some counties of Tibet. In one county, Winkler found that a harvester’s typical yield, about 10 specimens a day, is the cash equivalent of a week’s wage in the region. (The sustainability of Tibet’s high-pressure caterpillar fungus harvest is unknown, but the harvest has been going on for centuries.) Winkler has reported that Tibetans collected 50,000 kilos of caterpillar mushrooms in 2004, worth about $133 million. This sum is equal to 40 percent of the rural cash income nationwide, and 70 to 90 percent of incomes in production areas. Incredibly, this tiny parasitic fungus is the primary commodity of Tibet. The country is, as Winkler says, “a globally unique, fungally dominated rural economy.”
In 2008, the fungus—always attached to the worm—was selling for $6,000 to $13,000 a pound in Mainland China, Hong Kong, and San Francisco, depending on the quality. The most valuable specimens are those with large caterpillars and young, presporulated mushrooms, as the healing power of the fungus is believed to be greatest in the mycelium-filled worm. The primary market for the caterpillar fungus are the Chinese, and when I suggested to Winkler only half-jokingly that the Chinese may have had the fungus in mind when they occupied Tibet, he just gave me a significant look.
