The Wonderful World of Fungi, Part II
Importance of Fungi to Human Affairs
By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
Not only are fungi some of the most fascinating organisms found on earth because of their life cycles, modes of nutrition, growth habits, and habitats, but also because of the number of roles they play in human affairs. This blog is a brief survey of some of the roles that fungi play in the life of humans and some of the benefits and detriments caused by this group of organisms.
Perhaps the benefit of fungi to humans that first comes to mind is their edibility. Many fungi are edible, but if you or someone else collects mushrooms in the wild to eat, you must be extremely careful not to collect poisonous species that may resemble edible ones. Edible mushrooms that are easy to recognize or which are available in stores for purchase include the following: the common button mushroom (Agaricus bisporus), which is perhaps the best known edible species; the shitake (Lentinus edodes); the oyster mushroom (Pleurotus sp.); the ear fungus (Auricularia auricula); and paddy straw mushroom (Volvariella volvacea). These are all important edible species consumed in great quantities around the world. Other, more expensive and thus less frequently consumed edible mushrooms are the truffles (Tuber melanosporum or other species of Tuber). Truffles are considered delicacies by most people and are highly prized by fungal connoisseurs. These mushrooms (they are ascomycetes and not basidiomycetes however) grow underground in association with certain tree roots and must be hunted using dogs or pigs to “sniff-out” the underground fruiting body. One other genus of fungi that is considered a delicacy but which is not readily available in the marketplace is Morchella, the genus of fungi commonly known as morels.
Some fungi are edible because they are part of certain cheeses. These fungi when present in the cheese serves to putrefy the cheese protein and give the cheese a very distinctive taste. Such fungal cheeses include blue, Roquefort, and Camembert cheese.
One other fungus that is edible and is economically the single most important fungus to humans is yeast, Saccharomyces cerevisiae. Without yeast, there would be no baking and brewing industries as we know them. Consider all the products consumed that are dependent upon yeast for their manufacture, and the jobs created because of the consumption of these yeast products.
Fungi also play a role in various manufacturing processes that produce materials humans consume as food or drugs, or use directly or indirectly in other ways. For example, fungi are involved in the production of steroids and hormones. They are also used in the production of various organic acids such as citric acid and gluconic acid. Some fungi are also used in the production of medicinal drugs; the antibiotics penicillin and cephalosporin for example, and the immune system inhibitor cyclosporine, which is used to reduce rejection of transplanted organs. The fungus that causes ergot of rye produces alkaloids which are derivatives of lysergic acid. These compounds can be used to stimulate uterine contractions which help to prevent postpartum hemorrhage, and to constrict blood vessels in the brain to help in relief of migraines.
Fungi play crucial roles in natural ecosystems. In fact, many plants are dependent on fungi for their survival. Some 70% of all plants in nature form symbiotic relationships between the plant’s roots and select fungi. These symbiotic associations are called endomycorrhizae, a term meaning fungal root. The plant roots live in a mutualistic relationship with fungal hyphae that live inside of the plant roots (endo-). All species of grass form these endomycorrhizae as do most herbaceous plants, and some trees. Other plants form ectomycorrhizae, which are also symbiotic associations between plant roots and fungal hyphae, but these fungi grow on the outside of the plant roots. These ectomycorrhizae are mostly confined to a few families of trees in the temperate and boreal regions of the world (pines, spruces, etc., and the oaks, beeches, and birches).
The other crucial role played by fungi in natural ecosystems is that of scavenger and mineral recycler. Fungi are the dominant organisms breaking down cellulose and lignin, the major components of plant cell walls. The fungi convert these large polymers into materials that can be used by other organisms and thus are important in the nutrient and mineral recycling seen in natural ecosystems.
Fungi are also important in human affairs because of their destructive abilities. Fungi are major contributors to the spoilage of stored foods and the destruction of most manufactured materials except plastics and pesticides. If the product is a natural one, you can assume that there will be some fungus that can grow on it. Examples of products attacked by fungi include wood, plant fibers, leather, cloth, etc.
Fungi are the major cause of plant diseases. Diseases such as wilts, blights, rusts, smuts, rots, and mildews are all caused by various fungi. There is a constant battle to develop new plant strains or new fungicides to reduce the destruction caused by fungi to various crop plants. Consider the devastation caused by chestnut blight, Dutch elm disease, corn smut, and wheat rust, just to name a few.
In addition to causing various plant diseases, fungi also are responsible for some human and animal diseases. There are about 150 fungal species known to be pathogenic to humans. Many superficial skin diseases are caused by fungi: thrush, athlete’s foot, jock itch, barber’s itch, etc. In addition, there are also various systemic mycoses that result from fungal spores gaining access to deeper tissues of the body: candidiasis, aspergillosis, histoplasmosis, blastomycosis, etc. Generally, systemic mycoses result from fungi that are described as opportunistic pathogens; that is, these fungi are normally saprobes but if given the opportunity they will grow in humans and cause disease. The links below are of a table and concept map listing common systemic mycoses and their causative agents.
One other way in which fungi can cause harm to humans is through ingestion of poisonous fungi. There are perhaps 30-40 species of fungi that are considered significantly poisonous out of the several thousand species of fungi known. The principal group of fungi responsible for fungal poisonings are the gill fungi; basidiomycetes that produce mushrooms that bear their basidia on structures called gills.
Fungi have been, and continue to be used as experimental tools in research laboratories. Fungi are easily cultured, occupy little space, multiple rapidly, and have short life cycles. All of these features make them ideal experimental organisms to work with. Fungi have been used in the study of metabolic pathways, growth and development, and differentiation. They have also played a role in genetic studies (for example, the “one gene one enzyme hypothesis” proposed by Beadle and Tatum in 1941 was based on their studies using the fungus Neurospora), and in the investigation of mechanisms of cell division and development.
As you can glean from the above paragraphs, fungi are extremely important in human affairs, directly and indirectly. The next time you eat bread, or see mold on it, or you see a mushroom in your lawn, or you have an outbreak of athlete’s foot fungus, then consider the significant role fungi play in your life and in those of all humans.