Fungi (Encyclopedia of Science)
Fungi (plural of fungus) are one of the five kingdoms of organisms. Kingdoms are the main divisions into which scientists classify all living things on Earth. The other kingdoms are: Monera (single-celled organisms without nuclei), Protista (single-celled organisms with a nucleus), Plantae (plants), and Animalia (animals).
Fungi constitute a large and diverse group of organisms. The kingdom of fungi is divided into four major groups: conjugating fungi, sac fungi, club fungi, and imperfect fungi. Mushrooms, molds, yeasts, and mildew are all fungi. Biologists have estimated that there are more than 200,000 species of fungi in nature, although only about 100,000 have been identified so far. The scientific study of fungi is called mycology.
The different groups of fungi have different levels of cellular organization. Some groups consist of single-celled organisms that have a single nucleus per cell. (A nucleus is a membrane-enclosed structure within a cell that contains the cell's genetic material and controls its growth and reproduction.) Other groups consist of single-celled organisms in which each cell has hundreds or thousands of nuclei. Still others consist of multicellular organisms that have one or two nuclei per cell. The bodies of multicellular fungi usually consist of slender, cottony filaments called hyphae. A...
(The entire section is 1241 words.)
Show us the love and view this for free! Use the facebook like button, or any other share button on this page, and get this content free!free!
Want to Read More?
Subscribe now to read the rest of this article. Plus get complete access to 30,000+ study guides!
Fungi (Science Experiments)
Decomposers: Food source for a common fungi
Design Your Own Experiment
As a way of organizing living things, scientists have created five main classifications called (some scientists use more than five). Each kingdom breaks down into smaller and smaller classifications. Plants and animals, for example, are two of these kingdoms. FungiKingdom of various single-celled or multicellular organisms, including mushrooms, molds, yeasts, and mildews, that do not manufacture their own food. form another kingdom.
There are thousands of types of fungi. They are both single-celled and multicelled; living on land and in water. They include the microscopic, such as yeasts, and the relatively mammoth, such as mushrooms. Scoop up a single teaspoon of topsoil and you will find about 120,000 fungi. As of 2003, the largest living organism on Earth is a fungus, dubbed the humongous fungus, which extends about 3.5 miles (5.6 kilometers).
Fungi play a vital role in Earth's cycle of life. They decompose or break down dead bugs and plant material, such as leaves, converting their components into elements that living organisms can reuse. They are an essential...
(The entire section is 4513 words.)
Show us the love and view this for free! Use the facebook like button, or any other share button on this page, and get this content free!free!
Fungi (Encyclopedia of Nursing & Allied Health)
Fungi are eukaryotic organisms (each containing a membrane-bound nucleus) that develop from reproductive bodies called spores. Fungi may be the cause of any number of diseases in humans, animals, and plants; fungal infections are called mycoses (singular, mycosis).
Mycology is the branch of science that studies organisms of the kingdom Fungi. Scientists estimate that over 200,000 species of fungus exist in nature. These species include yeasts, moulds, mildews, mushrooms, lichens, and smuts.
There are a number of characteristics that fungi share: they are eukaryotic (containing a nucleus that is bound by a nuclear membrane); they develop from reproductive bodies called spores; their cell walls are composed mostly of chitin, a nitrogen-containing carbohydrate; and they are heterotrophic (they cannot synthesize their own food and therefore absorb food from an external source through their cell walls).
Most fungi obtain their nutrients from dead organic matter and are called saphrophytes. Saphrophytes play an important ecological role in the decomposition of dead plants, animals, and other organic matter: they release large amounts of carbon dioxide into the atmosphere and recycle nitrogen and other important nutrients for use by plants and other organisms. Other fungi are parasites (obtaining their nutrients from a living host organism in a relationship that usually harms the host) or mutualists (involved in a mutually beneficial relationship with another organism).
Another important characteristic of fungi is that they do not contain chlorophyll. Chlorophyll is a green pigment that enables plants and such other photosynthetic organisms as algae and cyanobacteria to absorb energy from sunlight and use it to synthesize carbohydrates (photosynthesis). Because fungi are not reliant on sunlight as an energy source, they can grow in dark or low-light environments and in directions not normally observed in plants.
Most fungi may be classified according to two major growth forms: yeasts or molds. Yeasts are round, unicellular (single-celled) organisms that form a vegetative body called a thallus. The thallus may consist of cells in groups or in branched chains called pseudo-hyphae. Examples of yeasts include Saccharomyces cerevisiae, used in making bread and alcoholic beverages; and Candida albicans, the causative agent of yeast infections.
Molds, on the other hand, are composed of long filaments called hyphae (singular, hypha). Hyphae may be further classified as septate (containing cross walls) or aseptate. A mass of hyphae is called a mycelium.
Whereas yeast cells each contain a single nucleus, cells in septate hyphae may be uninucleate (containing one nucleus), binucleate (containing two nuclei), or multinucleate (containing many nuclei). An example of a mold is Penicillium roqueforti, used to make blue cheese.
Some fungi are dimorphic: they may exist in either yeast or mold form. What form a fungus assumes depends on such environmental factors as the temperature or nutrients present. Some examples of dimorphic fungi include Histoplasma capsulatum and Coccidioides immitis.
All fungi can reproduce asexually by the production of single-celled structures called spores. The number of chromosomes (structures in the nucleus containing genetic material) remains unchanged when cells duplicate their genetic material and then divide. This is not the ideal state for a fungus and is thus called the imperfect state. (It is often observed in the laboratory when fungi that are normally pathogenic to humans are allowed to reproduce.)
Sexual reproduction can also occur in most fungi and is called the perfect state. In this process, one cell divides to become two haploid cells (each containing a single set of unpaired chromosomes). Two cells can then fuse together to become a diploid cell (containing a full set of chromosomes); that cell can then divide.
Role in human health
Some fungi have been found to be directly or indirectly beneficial to humans, while others are pathogenic (disease-causing). Still others are pathogenic to plants and animals important in the food chain.
Different yeasts in the genus Saccharomyces are employed by bakers, brewers, and vintners to make their bread, beer, or wine. For instance, S. cerevisiae is commonly used as baker's yeast and in the production of ales. Candida milleri is a yeast used in conjunction with an acid-producing bacteria to yield sourdough bread.
Various species of mushrooms are cultivated specifically for human consumption. These include Agaricus bisporus (accounting for 38% of the world's cultivated mushroom supply), Lentinus edodes (shiitake mushrooms), Volvariella volvacae (the paddy straw mushroom), and the Pleurotus family (oyster mushrooms). Other edible fungi include truffles (fungi of the family Tuber that grow in a special subterranean (mycorrhizal) association with certain trees), morels (of the Morchella family), and the blue-green mold of the Penicillium family that is essential in the production of certain cheeses.
Medicinal and recreational drugs
Discovered in 1929, a metabolite of the fungus Penicillium notatum (later to be called penicillin) became the first antibiotic (a substance produced by a microorganism that can selectively treat an infectious disease). Other fungi that are the source of clinically important antibiotics include those in the family Streptomyces: S. nodosus (amphotericin B), S. erythreus (erythromycin), S. fradiae (neomycin), S. griseus (streptomycin), S. orientalis (vancomycin), and S. rimosus (tetracycline).
Some species of fungi are known as hallucinogens (substances inducing false sensations in the absence of true stimuli) and have been used by many cultures during religious ceremonies (for example, Amanita muscaria). Claviceps purpurea (the ergot fungus) and fungi of the Psilocybe family are also known for their hallucinogenic effects.
Phycomyces blakesleeanus is a fungus that grows on animal feces in nature. The sporangiophores (the stalks on which spores are produced) of Phycomyces have been shown to respond to a variety of stimuli, including light, gravity, wind, and nearby objects. One important finding was that the light sensitivity of the sporangiophore is about the same as the eyes of humans. Furthermore, like humans, the sporangiophore can adapt to a one-billion-fold change in ambient light intensity.
Biologists have recently shown that Neurospora crassa, also known as red bread mold, can produce spores at approximately 24-hour intervals (known as a circadian rhythm) when in a constant environment. The fungus is therefore being used as a model organism for investigating circadian rhythms, which occur in many different organisms including humans.
Common disease and disorders
Human mycoses can be classified as superficial, cutaneous, subcutaneous, systemic, or opportunistic.
Superficial and cutaneous mycoses
These fungal infections do not invade underlying muscle or bone and are mostly restricted to the outer layers of the skin, nails, and/or hair. Superficial mycoses involve only the outermost layers of skin and result in a change in hair or skin pigment. For example, tinea nigra, caused by Exophiala werneckii, results in black lesions on the skin. Piedraia hortai, the causative agent of black piedra, creates hard dark-colored nodules on scalp hair, eyebrows, and/or eyelashes.
Cutaneous mycoses are generally caused by infection with a dermatophyte (a skin-infecting fungus). Common families of dermatophytes are Epidermophyton, Microsporum, and Trichophyton. Some of the more commonly seen cutaneous infections include:
- tinea corporis (body, "ringworm")
- tinea capitis (scalp, eyebrows, eyelashes)
- tinea barbae (beard, "barber's itch")
- tinea cruris (groin, "jock itch")
- tinea inguium (nails)
- tinea pedis (feet, "athlete's foot")
In the case of subcutaneous fungal infection, muscle, bone, connective tissue, and/or overlying skin may be involved. Subcutaneous mycoses may begin at the site of a laceration or even a seemingly innocuous scratch or puncture wound; fungi are introduced from soil or plant material. These mycoses, however, typically remain localized rather than spread from the site of infection. Sporotrichosis (caused by Sporothrix schenckii) and mycetoma (caused by Madurella grisea, among others) are two noted exceptions; sporotrichosis may spread along the lymphatic system, and mycetoma to deeper muscle and bone.
Cyanobacteriahotosynthetic bacteria, commonly known as blue-green algae.
Dermatophyte fungus that can cause a skin infection.
Hyphaellular unit of the fungi; typically a branched and tubular filament.
Lichen fungus that grows a symbiotic relationship with algae.
Meningitisnflammation of the meninges, the membranes surrounding the brain and spinal cord.
Metabolite substance produced by way of a metabolic process.
Morphologyhe study of the shape and structure of an organism.
Mutualismlose relationship of two or more organisms, which typically involves exchange of food or other resources.
Mycorrhizaubterranean symbiotic relationship between a fungus and a plant root.
Septumall that separates the cells of a fungal hypha into segments.
Systemic fungal infections usually involve more than one type of body tissue. The lungs are often a site of primary infection when airborne spores are inhaled. Often the primary infection is asymptomatic (shows no signs of infection) or resolves quickly. If the fungus spreads to the bloodstream, however, it may disseminate to other organs or systems. The following are the most commonly seen systemic mycoses:
- Blastomycosis, caused by Blastomyces dermatitidis; begins as a pulmonary infection but may disseminate to bone and/or skin.
- Coccidioidomycosis, caused by Coccidioides immitis; begins as a pulmonary infection (although 60% of infections are asymptomatic) but may disseminate to the central nervous system, bone, and/or skin.
- Cryptococcosis, caused by Cryptococcus neoformans; begins as a pulmonary infection but may disseminate to the central nervous system to cause meningitis.
- Histoplasmosis, caused by Histoplasma capsulatum; begins as a pulmonary infection but may disseminate to the lymph nodes, spleen, and/or liver.
- Paracoccidioidomycosis, caused by Paracoccidioides immitis; begins as a pulmonary infection but may disseminate to the mucous membranes, lymph nodes, and/or skin.
Opportunistic fungi do not normally cause disease in healthy humans, but can cause infection in individuals who are immunocompromised, such as those with acquired immune deficiency syndrome [AIDS] or those who have undergone organ transplantation. Some important opportunistic mycoses include:
- Aspergillosis, a mycosis caused by members of the Aspergillus family. Common mechanisms of infection include hypersensitivity (an allergic reaction); local pulmonary infection; opportunistic infection (leading to pneumonia and the development of a characteristic "fungal ball"); and systemic infection (leading to abscesses in the brain, liver, kidneys, skin, or bone.
- Candidiasis. Candida albicans is a yeast that causes oropharyngeal candidiasis, also known as thrush. Thrush is an often-seen opportunistic infection in patients with acquired immune deficiency syndrome (AIDS). Candida albicans is also the cause of the majority of cases of vulvovaginitis (yeast infection).
Fisher, Frances W. Fundamentals of Diagnostic Mycology. Philadelphia: W. B. Saunders Company, 1998.
Spicer, W. John. Clinical Bacteriology, Mycology, and Parasitology. London, UK: Churchill Livingstone, 2000.
"Mycology." Microbiology and Immunology On-line Textbook. University of South Carolina. 3 April 2001. 2 August 2001. <<a href="http://www.med.sc.edu:85/book/mycolsta.htm">http://www.med.sc.edu:85/book/mycolsta.htm>.
"Mycoses."Doctor Fungus Website. 12 April 2001. 2 August 2001. <<a href="http://www.doctorfungus.org/Mycoses/index.htm">http://www.doctorfungus.org/Mycoses/index.htm>.
"Penicillin and Other Antibiotics." The Microbial World
Website. University of Edinburgh. 2 August 2001. <<a href="http://helios.bto.ed.ac.uk/bto/microbes/penicill.htm">http://helios.bto.ed.ac.uk/bto/microbes/penicill.htm>. "
What are yeasts?" Yeast WWW Virtual Library. Stanford University. 2 August 2001. <<a href="http://genome-www.stanford.edu/Saccharomyces/VL-what_are_yeast.html">http://genome-www.stanford.edu/Saccharomyces/VL-what_are_ye... >.
Stéphanie Islane Dionne
Fungi (Encyclopedia of Food & Culture)
FUNGI. Fungiing. fungus; from the Greek sphongis (sponge)re nonphotosynthetic and thus must absorb nutrients from organic matter formed by other organisms. The great majority of fungi obtain their food from dead organic matter and hence are known as saprophytes; a relatively small percentage derive their food from other living organisms and are known as parasites. Fungi may be unicellular (yeasts) or multicellular (mushrooms) and their cell walls usually contain chitin or cellulose and bglucan. They may produce sexually or asexually by means of spores that are roughly comparable with the seeds of higher plants.
The fungal kingdom offers enormous biodiversity with over seventy thousand known species and an estimated 1.5 million species. According to molecular evidence (16S-like ribosome RNA sequences), the fungi may have originated from protozoan ancestors before the kingdoms Animalia and Plantae split; there is strong evidence that Fungi are closer to Animalia than Plantae (Hawksworth et al.). Fungi are associated with some of the earliest remains of land plants. Some scientists believe that lichens (a stable self-supporting association of a fungus and an alga) might be transmigrants, the earliest colonizers of land.
Fungi have contributed to the shaping of humankind's welfare since the beginning of civilization. Fungi are recognized as both beneficial and harmful in their relationship to humans although this role is predominantly beneficial. They are responsible for a major portion of food deterioration in developing countries; however, the preservative effects of fermentation of foods and beverages with fungi are well-known benefits, including organic acids, alcohol, antibiotics, pigments, vitamins, growth regulators, immunomodulating agents, and enzymes. Finally, various types of edible mushrooms are consumed as an important part of human diets in many countries.
Fungi and Food Processing
Fungi used in food processing have been an integral part of the human diet since the beginning of civilization. In such foods, fungi are the agents responsible for imparting special flavors, textures, odors, or consistencies to food products. Fungi such as Aspergillus spp., Rhizopus spp., Penicillium spp., Neurospora spp., Cladosporium spp., and Mucor spp., as well as yeasts and many others have long been used to process a number of food products from soybeans to peanuts, rice, gram, maize, cassava, taro, and cacao beans.
Fungal enzymes. Food formulation using enzymes derived from fungi has undergone a rebirth in recent years. Enzyme suppliers have improved their ability to supply single-activity enzymes that do not have undesirable side activities (see Table 1 for a list of commercial fungal enzymes and their uses). Enzyme products have found increasing application for improving product clarity and yield and in replacing costly physical processes such as heating.
Cheese manufacture. Two general types of cheese are made with fungi as the ripening agents. Roquefort cheese is an example of cheese that is ripened primarily by growth of fungi (Penicillium roquefortii) throughout the cheese mass. Brie cheese is an example of one type of soft cheese that is ripened by the growth of fungi (Penicillium camemberti) on the outside of the cheese mass. In both types of cheeses, the fungi grow and release protein and fat-degrading enzymes that soften and ripen the cheese. Roquefort cheese requires about two months to ripen while Brie cheese requires only about one month to ripen.
Baker's yeast. Leavening, a process whereby batter or dough is caused to rise via the production of gas, especially carbon dioxide, was first discovered in Egypt. Today, most of the bread, cakes, cookies, and the like consumed by the public are prepared from leavened batter
|List, source, and uses of enzymes derived from fungi for food manufacture|
|α -Amylase, amyloglucosidase||
|Hydrolysis of starch in production of beer, bread; manufacture of high-fructose syrups|
|α-Galactosidase||Mortierella vinacea||Hydrolysis of raffinose to sucrose and galactose during sugar refining|
|Remove excess hydrogen peroxide formed during cake baking or that may be added during pasteurization of milk and cheese|
|Improve palatability of low-quality vegetables, accelerate drying of vegetables, alter texture of foods, increase flavor of commercial mushrooms|
|Manufacture of instant coffee|
|Increases sweetness in confections; yields soft center in chocolate-covered candies|
|Hydrolysis of lactose in milk products, enabling their use by lactose-intolerant individuals; production of syrups for use as sweetening agents|
|Used for flavor development in cheese, chocolate crumb, apple wine, and cooking fats; improved whipping properties of egg whites; fish processing|
|Naringinase||Aspergillus niger||Reduce bitter flavonone glycoside derivative found in some citrus products|
|Nuclease||Penicillium spp.||Flavor enhancers|
|Remove turbidity from fresh fruit juices; removal of pectins before concentrating juice; clarifying agent in wine|
|Protease||Aspergillus spp. Mucor pusillus||Meat tenderizer; remove bitter flavors, replace rennin in cheese manufacture, chill-proofing of beer; reduce elasticity of glutin proteins in bread|
|Rennet||Mucor spp.||Milk coagulation in cheese manufacture|
|Tannase||Aspergillus niger||Treat insoluable material that forms during manufacture of instant tea|
|SOURCE: Adapted from: Beuchat (1987) and Moore-Landecker (1995)|
or dough. Most cakes and cookies are leavened chemically (by using baking powder) while most bread is leavened by yeasts (such as Saccharomyces cerevisiae). Yeasts develop and reproduce by producing buds on mother cells that subsequently enlarge and produce more buds. During growth, carbohydrates in the dough are metabolized to carbon dioxide that is trapped in the dough in the form of bubbles. During the leavening process, alcohol may accumulate in the dough to as high as 0.5 percent. The alcohol is driven off during baking and helps give the bread a pleasant aroma.
Mushrooms have a long history of human consumption. Traces of puffball fungi have been found in Stone Age settlements. Over 4,500 years ago in ancient Egypt only pharaohs were permitted to eat mushrooms, which they believed were "sons of the gods" sent down to earth on lightning bolts announced by claps of thunder. The legend that mushrooms may have originated from thunder and lightning also existed among people of other ethnic groups. In Roman folklore, some fungi were believed to spring from the ground in places struck by a thunderbolt. In the Hindu tradition, there was a god named Soma that manifested himself to the priests in the form of hallucinogenic fluids. Some scientists believe that Soma was the fly mushroom, Amanita muscaria. A similar legend may have existed among the inhabitants of the highlands of Guatemala and Mexico, where even today the people refer to A. muscaria by a common name meaning thunderbolt (Lowy).
Cultivated species. The cultivation of edible mushrooms worldwide reached 6.16 million metric tons in 1997, up from 1.26 million tons in 1981 (Table 2; Chang). This represents a 12 percent annual increase. Six mushroom genera accounted for 87 percent of the total mushroom supply (Table 2). These were Agaricus (31.8%), Lentinula (25.4%), Pleurotus (14.2%), Auricularia (7.9%), Flammulina (4.6%), and Volvariella (3%). China produced 3.92 million tons of mushrooms in 1997, or 63.6 percent of the total world output. The major mushroom of commerce in China is L. edodes, which accounts for 35 percent of the total output for that country. China currently produces 88 percent of the total world production of L. edodes.
Agaricus bisporus (button mushroom). The cultivation of the button mushroom originated in the Paris region in France. Melon growers in this region discovered how mushrooms could be grown and started cultivating them in 1650. By the mid 1700s it was discovered that A. bisporus could grow without light, and that very favorable conditions for growing mushrooms prevailed in subterranean tunnels and caves. As a result of this discovery,
|World production of cultivated edible mushrooms in 1981, 1990, and 1997|
|Species||Fresh Wt (x 1,000 t)||%||Fresh Wt (x 1,000 t)||%||Fresh Wt (x 1,000 t)||%|
|SOURCE: Chang, 1999|
successful culture was undertaken inside the numerous caves that were excavated for building stones and for gypsum. The caves presented, from a climatic point of view, several advantages over the previous growing conditions in open air. Factors such as temperature and relative humidity were much more constant in caves compared with aboveground conditions.
From France, mushroom cultivation spread to other parts of the world. The business grew and soon spread to England and other countries. By 1825, the first mushroom crops were being produced in caves in Holland. In 1865, mushroom culture entered the United States via England and the first mushrooms were grown on a small scale on Long Island, New York; by 1870 the industry had begun to develop.
The button mushroom is produced commercially on a selective substrate prepared by composting mixtures of wheat straw, hay, corncobs, horse manure, or combinations thereof. The finished compost should have a nitrogen (N) content of 2.5 percent, and to reach such a level, nitrogen-rich supplements must be added. Inorganic nitrogen supplements can be added but only to provide part of the necessary amount. Organic sources of nitrogren include oilseed meal, brewers' grain, malt sprouts, and poultry manure.
Once the compost has been prepared, it is seeded with mushroom spawn that is prepared from a mother culture maintained by a spawn laboratory. Spawn is prepared by inoculating a pure culture of the mushroom onto steam-sterilized grain, usually rye or millet. Approximately one liter (500 g) of spawn is used to seed 0.5 m2 of production surface that is contained in trays or beds inside environment-controlled production houses. Spawn run (vegetative growth of the mycelium) lasts ten to fourteen days, then a layer of neutralized peat moss (casing) is placed on top of the colonized compost to stimulate production of mushrooms. Approximately ten to fourteen days after casing, mushrooms are ready for harvest.
Lentinula edodes (shiitake). Production of shiitake worldwide increased more than sevenfold in the fourteen-year period from 1983 (207,000 t) to 1997 (1,573,000 t; Chang). Most of this increase occurred in China, where more than ten million part-and full-time farmers cultivate shiitake. Shiitake is widely consumed in China, yet one-third of production is exported. In 1997, China produced approximately 88 percent of the total world output (Chang). In the United States, production of shiitake is a relatively new enterprise, having begun only in the late 1970s. In 1990, the United States produced 1,123 tons of shiitake and by 1999 production reached 3,941 tons, a 3.5-fold increase (USDA). This increase in production was due, in part, to increased production efficiency and to increasing consumer demand. Farmers have learned to provide the specialized management this crop requires, thereby reducing production costs. The amount of controlled-environment production surface devoted to growing shiitake on synthetic logs has increased 2.9 fold from 1990 to 1999 (74,200 m2 to 212,400 m2, respectively).
Sawdust is the most popular basal ingredient used in synthetic formulations of substrate for producing shiitake in the United States, but other basal ingredients may include straw, corncobs, or both. Starch-based supplements (200 percent dry weight) such as wheat bran, rice bran, millet, rye, and maize may be added to the mix. These supplements serve as nutrients to provide a more optimal growth medium (Royse).
Pleurotus spp. (oyster mushroom). Oyster mushroom production increased at a rapid rate worldwide during the 1980s and then decreased slightly during the 1990s (Table 2). From 1986 to 1997, oyster mushroom production increased from 169,000 tons to 917,000 tons (a 5.4-fold increase). China was responsible for most of the production increase. In the United States, production of oyster mushrooms was 1,647 tons in 2001, up 2 percent from the previous year (USDA).
In the United States, the primary ingredients used for Pleurotus spp. production are chopped wheat straw or cottonseed hulls or mixtures thereof. After completion of pasteurization (140°F [60°C] for one to two hours) the substrate is cooled and spawned with the desired strain. There are several species of oyster mushrooms cultivated, with various colors of fruiting body. In Japan, bottle production of oyster mushrooms is most common. Substrate is filled into bottles, sterilized, and inoculated with Pleurotus spawn. Upon completion of the spawn run, bottle lids are removed and mushrooms emerge from the surface of the substrate. After the mushrooms are harvested they are weighed and packaged for shipment to market.
Auricularia spp. (wood ear mushroom). Total production of Auricularia spp. in 1997 exceeded 485,000 metric tons (fresh weight; Table 2). This value is an increase of 366,000 tons or fourfold over 1986 levels (Chang). Auricularia spp. production now represents about 8 percent of the total cultivated mushroom supply worldwide.
Auricularia auricula and A. polytricha commonly are produced on a synthetic medium consisting of sawdust, cottonseed hulls, bran, and other cereal grains or on natural logs of broadleaf trees. For synthetic medium production of Auricularias, the substrate may be composted for up to five days or used directly after mixing. The medium is filled into heat-resistant polypropylene bags and sterilized (substrate temperature 240°F [121°C]) for sixty minutes. After the substrate has cooled, it is inoculated
Flammulina velutipes (enokitake). Worldwide production of F. velutipes has increased from about 100,000 metric tons in 1986 to about 285,000 tons in 1997. Japan is the main producer of enokitake. In the United States, enokitake production has increased at an estimated rate of 25 percent or more per year for the last four years. However, only about 60 tons of enokitake were produced in the United States in 2001.
Production of most enokitake in Japan is based on synthetic substrate contained in polypropylene bottles. Substrates (primarily sawdust and rice bran; 4:1 ratio) are mechanically mixed and filled into heat-resistant bottles with a capacity of 800 to 1,000 ml. Sawdust primarily from Cryptomeria japonica, Chamaecyparis obtusa, or aged (nine to twelve months) Pinus spp. appears to offer the best yields. In the United States, a sterilized, bran-supplemented medium, consisting primarily of corncobs, serves as the primary medium. When the substrate is fully colonized, the original inoculum is removed mechanically from the surface of the substrate and the bottles may be placed upside down for a few days.
To further improve quality during fruiting, temperatures are lowered to 37° to 46°F (3 to 8°C) until harvest. As the mushrooms begin to elongate above the lip of the bottle, a plastic collar is placed around the neck and secured with a Velcro® strip. This collar serves to hold the mushrooms in place so that they are long and straight. When the mushrooms are thirteen to fourteen cm long, the collars are removed and the mushrooms are pulled as a bunch from the substrate. The mushrooms then are vacuum packed and placed into boxes for shipment to market.
Grifola frondosa (maitake). Japan is the major producer and consumer of maitake. Commercial production of maitake in Japan began in 1981 (325 t) and by 1997 reached 32,000 tons (a 98-fold increase). Maitake is produced primarily in the Japanese provinces of Niigata, Nagano, Gunnma, and Shizuoka. Other countries, such as the United States, began maitake production in the early 1990s. Maitake production in the United States in 2001 was estimated at about 84 tons.
Most maitake is marketed as food. However, maitake has been shown to have both antitumor and antiviral properties. Powdered fruit bodies are used in the production of many health foods such as maitake tea, whole powder, granules, drinks, and tablets. Maitake also is believed to lower blood pressure, reduce cholesterol, and reduce the symptoms of chronic fatigue syndrome.
Commercial production of most G. frondosa is on synthetic substrate contained in polypropylene bottles or bags. A common substrate used for production is hardwood sawdust supplemented with rice bran or wheat bran in a 5:1 ratio, respectively. Other formulas include hardwood sawdust (70 percent based on oven dry weight basis) supplemented with white millet (20 percent) and wheat bran (10 percent). Some growers may add soil to the mix to stimulate fruit body formation. For production in bags, the moistened substrate is filled into micro-filtered polypropylene bags and sterilized to kill unwanted competitive microorganisms. After cooling (sixteen to twenty hours), the substrate is inoculated and the bags are heat-sealed and shaken to uniformly distribute the spawn throughout the substrate. Spawn run lasts about thirty to fifty days depending on strain and substrate formulation.
Volvariella volvacea (straw mushroom). Cultivation of V. volvaceae is believed to have begun in China as early as 1822. In the 1930s, straw mushroom cultivation began in the Philippines, Malaysia, and other Southeast Asian countries. Production of the straw mushroom increased from 54,000 tons in 1981 to about 181,000 tons in 1997 (about 3 percent of the total mushroom supply).
Many agricultural by-products and waste materials have been used to produce the straw mushroom. These include paddy straw, water hyacinth, oil palm bunch, oil palm pericarp waste, banana leaves and sawdust, cotton waste, and sugarcane waste. Volvariella is well suited for cultivation in the tropics because of its requirement for higher production temperatures. In addition, the mushroom can be grown on nonpasteurized substrate, which is more desirable for low-input agricultural practices.
In recent years, cotton wastes (discarded after sorting in textile mills) have become popular as substrates for straw mushroom production. Cotton waste gives higher and more stable biological efficiencies (30 to 45 percent), earlier fructification (four days after spawning) and harvesting (first nine days after spawning) than that obtained using straw as a substratum. Semi-industrialization of paddy straw cultivation on cotton wastes has occurred in Hong Kong, Taiwan, and Indonesia as a result of the introduction of this method.
Wild mushrooms. In many developing countries, the collection and sale of wild edible mushrooms has become an important source of income for many people in remote forested regions. Despite a relatively short growing season, wild mushrooms provide many families with 50 to 100 percent of their income. World trade in wild, edible mushrooms is estimated at more than $7 billion annually (Arora). The global trade in matsutake (Tricholoma matsutake), the most expensive wild mushrooms after truffles, is estimated at $3 to $5 billion. Matsutake may sell for as much as $200 apiece in Tokyo markets. The King Bolete (Boletus edulis; also known as porcini, cepe, borovik, etc.) is the most popular wild mushroom of Europe. These may be served fresh in some upscale restaurants. Dried boletes are famous for their concentrated flavor and choice aroma and are available year round from almost anywhere in the world. Other wild mushrooms available on world markets include chanterelles (Cantharellus cibarius), morels (Morchella spp.), hedgehog mushrooms (Hydnum repandum), lobster mushrooms (Hypomyces lactifluorum), candy caps (Lactarius fragilis), and cauliflower mushrooms (Sparassis crispa).
WARNING: Collecting and ingesting wild mushrooms without the presence of an expert to correctly identify specimens can be very dangerous and should be discouraged since there are several deadly mushrooms that look like edible wild ones.
Mycotoxins are chemical compounds produced by fungi growing on organic substances such as corn, cottonseed, or peanuts that, when ingested, have some undesirable effect on humans or on an animal consuming them. Adverse effects can range from vomiting to weight loss, various types of tumors, and in some cases, death. Over one hundred toxic compounds produced by fungi have been identified, and about forty-five of these occur in grain crops. Some mycotoxins are rare in occurrence while others such as aflatoxin are common in some years. The seriousness of the mycotoxin problem varies with the year, the crop being grown, and the intended use of the crop product. Most mycotoxins affect the blood, kidneys, skin, or central nervous system, and some may cause cancer.
The genera of fungi of greatest importance to humans with respect to natural poisoning outbreaks are Aspergillus, Penicillium, and Fusarium. The Aspergillus flavus group produces aflatoxins (at least eighteen types known) that are considered the most important from the viewpoint of a direct hazard to human health. Aspergillus flavus is a common fungus that is found in soil, air, and decaying plant residues. Infection by A. flavus and subsequent aflatoxin production can occur in the field, in transit, or in storage. Most reports indicate that infection occurs in the field, while aflatoxin production can occur whenever the product is exposed to favorable conditions, either in the field or in storage.
Control of aflatoxin includes prevention of fungal growth, removal of toxins, and inactivation of toxin. Most control efforts have been directed toward control of aflatoxins in peanuts and corn. Hand picking, electronic sorting, and air classification accomplish control of aflatoxin in processed peanut products. Removal of shriveled, rancid, or discolored kernels has proven the most practical way of limiting aflatoxin contamination in peanuts.
Arora, D. "The Global Mushroom Trade." California Wild 52, no. 4 (fall 1999):167.
Beuchat, Larry R. Food and Beverage Mycology. 2d ed. New York: Van Nostrand Reinhold, 1987.
Chang, S. T. "World Production of Cultivated Edible and Medicinal Mushrooms in 1997 with Emphasis on Lentinus edodes (Berk.) Sing. in China." International Journal of Medicinal Mushrooms 1 (1999):27382.
Findlay, W. P. K. Fungi: Folklore, Fiction, and Fact. Eureka, Calif.: Mad River Press, 1982.
Fine, Gary Alan. Morel Tales: The Culture of Mushrooming. Cambridge: Harvard University Press, 1998.
Friedman, Sara Ann. Celebrating the Wild Mushroom. New York: Dodd, Mead, 1986.
Hawksworth, D. L., P. M. Kirk, B. C. Sutton, and D. N. Pegler. Ainsworth and Bisby's Dictionary of the Fungi. Wallingford, U.K.: CAB International, 1995.
Lowy, B. "Amanita muscaria and the Thunderbolt Legend in Guatemala and Mexico." Mycologia 66 (1974): 18890.
Moore-Landecker, Elizabeth M. Fundamentals of the Fungi. 4th ed. Upper Saddle River, N.J.: Simon & Schuster, 1996.
Royse, Daniel J. "Specialty Mushrooms and Their Cultivation." Horticultural Reviews 19 (1997): 597.
United States Department of Agriculture. Mushrooms. Washington, D.C.: National Agricultural Statistics Service, Agricultural Statistics Board, 2001.
Wasson, R. Gordon. Soma: Divine Mushroom of Immortality. New York: Harcourt Brace Jovanovich, 1968.
Daniel J. Royse
Fungi (World of Microbiology and Immunology)
Fungi play an essential role in breaking down organic matter and thereby allowing nutrients to be recycled in nature. As such, they are important decomposers and without them living communities would become buried in their own waste. Some fungi, the saprobes, get their nutrients from nonliving organic matter, such as dead plants and animal wastes, clothing, paper, leather, and other materials. Others, the parasites, get nutrients from the tissues of living organisms. Both types of fungi obtain nutrients by secreting enzymes from their cells that break down large organic molecules into smaller components. The fungi cells can then absorb the nutrients.
Although the term fungus invokes unpleasant images for some people, fungi are a source of antibiotics, vitamins, and industrial chemicals. Yeast, a kind of fungi, is used to ferment bread and alcoholic beverages. Nevertheless, fungi also cause athlete's foot, yeast infections, food spoilage, wheat and corn diseases, and, perhaps most well known, the Irish potato famine of 1843847 (caused by the fungus Phytophthora infestans), which contributed to the deaths of 250,000 people in Ireland.
Fungi are not plants, and are unique and separate forms of life that are classified in their own kingdom. Approximately 75,000 species of fungi have been described, and scientists estimate that more than 90% of all fungi species on the planet have yet to be discovered. The fungi body, called mycelium, is composed of threadlike filaments called hyphae. All fungi can reproduce asexually by cell division, budding, fragmentation, or spores, although some reproduce sexually.
The main groups of fungi are chytrids, water molds, zygosporangium-forming fungi, sac fungi, and club fungi. Chyrids live in muddy or aquatic habitats and feed on decaying plants, though some live as parasites on living plants, animals, and other fungi. Water molds, distantly related to other fungi, play an important role as decomposers in aquatic habitats. Some, however, live as parasites on aquatic animals and terrestrial plants, including potato plants that can be destroyed by certain types of water molds. Zygosporangium-forming fungi also can be either saprobes, such as the well-known black bread mold, or parasites on insects, such as houseflies. Sac fungi, of which more than 30,000 species are known, include the yeast used to leaven bread and alcoholic beverages. However, many of these fungi also cause diseases in plants. Club fungi, numbering more than 25,000 species, include mushrooms, stinkhorns, and puffballs. While some fingi are edible, others produce deadly poisons.
See also Candidiasis; Chitin; Fermentation; Fungal genetics; History of the development of antibiotics; Lichens; Winemaking