Download fungi - Dr Magrann

FUNGI
Fungi can be found anywhere from athlete’s foot to spoiled food, and even on our dinner
plate. There are more than one million species of fungi, many of which are just
mushrooms. Fungi are more closely related to animals than to plants. The few fungi
that are single celled are called yeasts; most fungi are multicellular and are called
molds. They have cell walls made of chitin. Their threadlike fungal filaments are
called hyphae. Although a few species of fungi can cause disease, most fungi are
essential to our ecosystem. They break down organic material and recycle nutrients,
allowing other organisms to obtain nutrients that they need. Humans also benefit from
fungi in various industries such as agriculture, forestry, and products ranging from bread
to antibiotics.
Plants are autotrophs (they make their own food out of sunlight), but fungi are
heterotrophs like animals because they cannot make their own food. They cannot
run or fly in search of food as most animals can. But unlike animals, fungi do not
ingest (eat) their food. Instead, fungi are similar to bacteria because fungi use
extracellular digestion to obtain their nutrients. They digest their food while it is still
in the environment by secreting powerful enzymes into their surroundings. These
enzymes break down large molecules into smaller ones that the fungi can absorb and use.
Some fungi are decomposers which live off of dead animals, feces, and vegetation
(saprobes), some are parasites (live on a host, causing damage to the host; about 80% of
plant diseases are caused by fungi), and some are symbiotic (live with a host in a
relationship that is beneficial to the fungi as well as the host).
Fungi have a powerful impact on ecosystems and human welfare.
DECOMPOSERS
They are important decomposers in most ecosystems; they help to recycle organic
matter. They decompose organic material, including the tough cellulose of plant cell
walls. Some Fungi can even consume jet fuel and wall paint. Fungi and bacteria are
primarily responsible for keeping ecosystems stocked with the inorganic nutrients
essential for plant growth. Without fungi, carbon, nitrogen, and other elements would
become bound up in the soil and unavailable for use.
SYMBIOTIC RELATIONSHIPS WITH PLANTS AND ANIMALS
Most known species of fungi are not parasitic. Fungi have symbiotic relationships with
plants, algae, bacteria, and animals. All of these relationships have profound ecological
effects. Almost all vascular plants rely on fungi for essential nutrients.
Some fungi share their digestive abilities with animals, helping to break down plant
material in the intestines of cattle and other grazing mammals. Many species of ants and
termites take advantage of the digestive power of fungi by raising them in on “fungi
farms”. These insects even scour tropical forests in search of leaves, which they carried
back to their nests and feed to the fungi. The fungi break down the leaves into a
substance that the insects can digest. The fungi from these and farms have become so
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dependent on their caretakers that in many cases they no longer can survive without the
insects.
Fungi are found associated with the earliest plant fossils. They helped plants become
terrestrial by forming mycorrhizal (fungi roots) associations with plants and helping
early plants to extract mineral nutrients from hostile soils
LICHENS
A lichen is an association between a fungus and cyanobacteria or green algae.
Lichens are a mass of photosynthetic microorganisms (algae and bacteria) that are held in
place by fungi filaments. They form a green carpet that hugs the surface of rocks, logs,
trees, etc. The merger of fungus, algae, and bacteria is so complete that lichens are
actually given scientific names as though they were single organisms. There are more
than 13,000 species of lichens, making up 1/5 of all known fungi.
Each partner organism within lichens provides something that the others could not obtain
on their own. The algae provide carbon compounds, the bacteria provide nitrogen, and
the fungi provide a suitable environment for growth. The physical arrangement of the
fungi filaments allow for gas exchange, protects the other partners, and retains water and
minerals. Some fungi produce a toxin that prevents the lichens from being eaten by
animals. The free-living fungus called Penicillium (provides the antibiotic penicillin) is
believed to be a descendent of a lichen fungus.
Lichens are important pioneers on new land, rocks, and logs from burned forests.
They break down the surface by physically penetrating with their roots and chemically
breaking down the rock, and binding together particles of soil that blow in. In this way,
solid rocks and dead vegetation gradually break down into fertile soil. This makes it
possible for new plants to grow.
Some lichens are thousands of years old. Lichens can withstand severe drought and
can tolerate severe cold but as lichens are they are sensitive to air pollution.
They are particularly sensitive to sulfur dioxide and other poisons that can accumulate in
the air. The death of sensitive lichens is an early warning sign that air quality is
deteriorating.
PATHOGENS
About 30% of fungi make their living as parasites, mostly on plants. For example, Dutch
Elm disease has drastically changed the landscape in the northeastern United States when
it was accidentally introduced to the US on the logs that were sent from Europe to help
pay World War I debts. It was carried from tree to tree by bark beetles.
Fungi are also serious agricultural pests. Between 10% and 50% of the world's fruit
harvest is lost each year fungal attacks, such as black stem rust on wheat. Some of the
fungi that attack food crops are also toxic to humans. For example, a certain species of
mold called Aspergillus may contaminate improperly stored bread, peanuts, and jelly,
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where it secretes a carcinogenic (cancer-causing) liver toxin called an aflatoxin.
Therefore, a peanut butter and jelly sandwich is a triple whammy for aflatoxin. It
dissolves in the jelly, so scooping it off the top surface of the jar will not do any good. To
prevent aflatoxin, only buy peanut butter and jelly in the size jars you use up in a week,
keep them refrigerated (the bread, too), and use a clean knife each time. Don’t leave the
lid off for long, because that’s when it gets in.
Another example of a toxic fungus one that forms purple structures called ergots on rye
grains. If diseased rye is accidentally mixed into flour and eaten, poisons from the ergots
can cause ergotism, a condition characterized by gangrene, nervous spasms, burning
sensations, hallucinations, and temporary insanity. An epidemic of ergot system in 944
AD killed more than 40,000 people in France. One of the compounds from ergots is a
hallucinogen found in LSD.
Animals are much less susceptible to parasitic fungi than plants. Only about 50
species of fungi are known to parasitize humans and other animals, but these relatively
few species do considerable damage. The general term for a fungal infection is mycosis.
Mycosis of this skin includes the disease called ringworm, named because it appears as
circular red areas on this skin. Ringworm (not a worm, but a fungus) can appear on
almost any skin surface, including the hair of the head, beard, pubic hair, and bare skin.
It forms tiny watery blisters which are extremely itchy; when the blisters are scratched
open, the fungus is released and spreads to a new area. Fungal infections of the feet are
called athletes foot. You get it by just walking barefoot, exposing the skin to the air
where spores are. Although healthy skin is resistant to these spores, if there is a slight
scratch in the skin, the fungi can get in. Fungus can also infect the nails, causing them to
become thick, crumbly, and yellow. Fungal infections of the skin are relatively easy to
treat with anti-fungal creams, but nail fungus is extremely difficult to cure, and may
require harsh oral medicines that can be toxic to the liver.
Mycosis within the body (systemic mycosis) spreads throughout the body and is extremely
serious. They are typically caused by fungal spores that are inhaled. Histoplasmosis is a
disease from a fungus that is found in soil that is rich in nitrogen, especially caves with bat
droppings (guano). Such caves are moist, rich in nitrogen, and have dead organic material
there, which are ideal conditions for molds. Spelunkers are people who explore caves,
usually on their hands and knees. Their nose is close to the floor, so they inhale the spores.
Hunting dogs get it the same way. When you hear the word “cave”, think of Histoplasma.
San Joaquin Valley fever is a systemic mycosis which is a respiratory disease with
symptoms similar to tuberculosis. This organism differs from histoplasmosis in that it
requires long periods of dry (arid) weather, and then a heavy rain. That makes it endemic to
west Texas, Mexico, Baha, South America, southern California, Arizona, and New Mexico.
The blood of everyone who lives in the San Joaquin Valley tests positive for the organism,
but they don’t usually get the disease. That’s because you need to be exposed to a large
amount to get sick; therefore farmers are at risk. Caesar Chavez fought for the rights of
immigrant farm workers, who were given short tools to weed the farms, so their noses were
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close to the ground to inhale the spores. They also were not paid well and had poor nutrition,
so they would get the disease. Once the spores get into the lungs, the person has flu-like
symptoms, and then it can disseminate into the bones, skin, and brain. It is a recurring disease
with treatment but no cure. In large amounts, it is so deadly that it is now considered a
potential biological weapon.
Opportunistic mycosis is a fungus that only causes disease in people with a weakened
immune system. An example is a type of fungus that can cause pneumonia; it lives in
soil rich in nitrogen, especially bird droppings. It is common in urban areas (cities)
because of the pigeons. Not as common in rural (country) areas.
Another opportunistic mycosis is a species of yeast called Candida. It is a type of fungus
that is normally found in the moist areas of the skin such as the mouth and vagina. It
does not cause disease unless it invades through a break in the skin or excess nutrients
become available (such as after taking antibiotics), allowing it to grow in greater numbers
than normal. This is called a yeast infection. Antibacterial and antibiotic medicines do
not kill fungi; an antifungal agent is needed. If a female takes oral antibiotics for a
bacterial infection elsewhere in the body, the normal bacteria in the vagina can be killed
off as well, although antibiotics usually do not kill yeasts or other fungi. With the
elimination of bacteria that compete for nutrients, the yeasts to have extra food and grow
to excess, causing itchiness and a vaginal discharge.
Newborn infants do not have a strong immune system; as they pass through the vaginal
canal during birth, their mouth can pick up an excess number of Candida organisms
which causes an overgrowth in the mouth, a disease called candidiasis or “thrush”. AIDS
patients also have a weakened immune system, and are susceptible to candidiasis; so are
the elderly and people with diabetes. Candidiasis can also occur in wet areas of the skin
and is common among dishwashers. Candidiasis can be mistaken for “jock itch” or diaper
rash, which is a bacterial infection and requires a different type of medicine. Vaginal
yeast infections are the result of an overgrowth of a fungus.
One particular species of fungus called “black mold” has been the subject of many news
reports. Black mold thrives in damp buildings and has been implicated as the cause of a
wide variety of human diseases.
PRACTICAL USES OF FUNGI
The dangers posed by fungi should not overshadow the immense benefits we derive from
this remarkable species. We depend on their ecological services as decomposers and
recyclers of organic matter.
Mushrooms are a popular food, but they are not the only fungi we eat. The distinctive
flavors of certain kinds of cheeses, including Roquefort and blue cheese come from the
fungi used to ripen them. The soft drink industry uses a species of fungus to produce citric
acid for colas and soy sauce. Morels and truffles are expensive mushrooms which are highly
prized for their complex flavors. They can cost several hundred dollars per pound. Truffles
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are rare and delicious and sell for about $5 each! In the past, hunting dogs and pigs were used
to sniff out where truffles were growing in the woods.
Humans have used yeast to produce alcoholic beverages and raise bread for thousands of
years. The yeasts ferment sugars to alcohol and carbon dioxide, and so can be used to
make alcohol from grapes or used in bread to make it rise. It is also used to make beer.
Many fungi have great medical value as well. For example, a compound extracted from
ergots is used to reduce high blood pressure and to stop excess bleeding after childbirth.
Some fungi produce antibiotics that are essential in treating bacterial infections. In fact,
the first antibiotic discovered was from a fungus that made penicillin, when a mold
was found growing on a Petri dish as an accidental contaminant.
The same yeast used to make beer is also a studied in biotechnology. Scientists are
gaining insight into the genes involved in human diseases such as Parkinson's disease and
Huntington's disease by examining the genes in this yeast because its cells are easy to
culture and its genes are easy to manipulate.
Genetically modified fungi are being used in medicine and in industry. One of the
medical benefits of GM fungi is that they are used to produce certain medicines such as
insulin. One of the benefits in industry is to harness fungal metabolism to produce paper
pulp from rotted wood.
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