Fungi are one of the five types of microbes1.
Fungi are plant-like organisms, but unlike plants they do not have chlorophyll. Because of this they cannot
make their own food. Instead, fungi absorb food from dead organic matter. The function of fungus in the
ecosystem is to break down complex organic substances and recycle carbon and other elements.
Some fungi are biotrophic, meaning they feeding from living cells; others are necrotrophic, meaning they
kill cells and then feed on them. Most fungi feed on plant material rather than animal material.
The main types of fungus are:
- Moulds (also spelled mold), which have filaments; and
- Yeasts, which are usually single cells.
Some common fungal Diseases that affect humans are listed below.
The approximately 100,000 species of the Fungus kingdom are divided into four phyla,
based on sexual characteristics.
- Sac or Cup Fungi (Ascomycota) - 50,000 species including Hemiascomycetae (Brewer's yeast, bakers yeast, and nutritional yeast) and Truffle mushrooms;
- Club Fungi (Basidiomycota) - most other mushrooms (a.k.a. basidiocarp);
- Conjugation Fungi (Zygomycota) - including common bread mould;
- Imperfect Fungi (Deuteromycota) - fungi that are not easily classified, including most of the ones cited below under Diseases.
The lichens (Mycophycophyta) were formerly considered to be a fifth fungus pyhla, but this is no longer true.
Structure and form
The visible part of a fungus is usually a "fruiting body" such as a mushroom. This is usually a small portion
of the overall organism. The main body of most fungi is a web called the mycelium. The mycelium is made of very
fine threads called hyphae. The hyphae branch and intertwine throughout the fungus' food source (such as
soil or wood). A fungal mycelium is generally too fine to be seen by the naked eye, unless the hyphae are
packed densely together.
The cell wall of a fungus is made of chitin, which is also found in insects. This is something that distinguishes fungi from plants - the cell walls of plants are made of cellulose.
Fungi are capable of two types of reproduction:
The types of diseases caused by fungi can be divided into 3 major categories:
- Allergic reactions (sensitivity to fungal proteins);
- Toxicity reactions (consumption of fungal toxins); and
- Fungal infections (invasion of living tissue by a fungus)
The most well-known example of an allergic reaction to fungus is "toxic mould" and
"sick building syndrome" in buildings.
(This was in the news in April 2002. Celebrity Ed McMahon sued his insurance company over a botched repair that caused fungus to spread throughout his home, making his family ill and allegedly killing his dog, Muffin. On doctor's orders, the McMahons moved out of their six-bedroom home in September 2001. The suit was settled in May 2003 for $7.2 million US.) The resulting condition is Allergic fungal sinusitis which causes a variety of symptoms, and in extreme cases can result in anaphylactic shock. Note that while moulds are very common in buildings, and will grow anywhere that there is moisture, 'toxic' moulds such as Stachybotrys chartarum are very rare. More common indoor moulds include Penicillium (the basis for the drug Penicillin).
The most well-known examples of fungal toxins are toadstool poisoning.
Toadstools such as the Death cap (Amanita phalloides) and Destroying angel
(Amanita virosa, A. verna, A. bisporigera, A. ocreata) ultimately cause death due to
kidney and liver failure. Another famous example is the Liberty Cap or Magic Mushroom ( Psilocybe
semilanceata) which affects the central nervous system inducing a hallucinogenic response.
Another example is ergotism, a syndrome which can cause gangrene, hallucinations, and death.
It is caused by consumption of rye products contaminated with toxins produced by the mould Claviceps purpurea. This fungus' toxins may have caused illness and delirium in Salem, Mass. leading to the Salem witch trials!
Some fungal infections, called primary pathogens, can cause disease regardless of the
previous health of the victim. Others, referred to as opportunistic, affect people with immune systems
that are already weakened by other factors. Diseases caused by fungal infection include:
- Tinea including Ringworm (an infection of the hair, skin, or nails);
jock itch (tinea cruris); and athlete's foot (tinea pedis) -- caused by mould fungi called dermatophytes
- Oral thrush, yeast infection, diaper rash -- Technical name candidiasis -- caused by Candida albicans
- Histoplasmosis -- Begins in the lungs, spreads through the body -- caused by Histoplasma capsulatum
- Pneumocystis pneumonia -- Lung infection2 in people who are HIV-positive, especially children. -- caused by Pneumocystis carinii
Fungi are the major cause of disease in plants, accounting for over 70% of major crop diseases.
The Irish Potato Famine was caused by
an oomycete*, Phytophthora infestans. (The distinction between fungus and oomycete is fairly recent.)
Although P. infestans did not infect humans, humans were certainly affected by it!
* oomycete correction by cordyceps.
- The others are bacteria, viruses, protozoans, and helminths (worms).
- Most pneumonia is bacterial or mycoplasmic, this is the only fungal pneumonia.
- Other writeups in this node. This writeup began life as high school biology lecture outline. Some redundancies exist with other writeups in this node, both for completeness and because they were used as a source for this work. Care has been taken to minimize the redundancies.
- The remarkable Tom Volk's Fungi pages http://botit.botany.wisc.edu/toms_fungi/
- Salem: http://botit.botany.wisc.edu/toms_fungi/oct99.html
- Destroying angel: http://www.bluewillowpages.com/mushroomexpert/amanita_bisporigera.html