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None of the fungi are photosynthetic, a key difference
between fungi and the plants with which they were once grouped.
Fungi are widely distributed and are found wherever
moisture is present.
They digest insoluble organic matter by secreting
exoenzymes, then
absorbing the soluble nutrients through their cell wall. Fungi live in their food and digest
the
food that surrounds their "bodies"; animals engulf their food usually
prior to digesting it.
"Fungi are hetertrophs and must obtain preformed organic molecules from
the environment and modify them. Fungi secrete powerful enzymes that enable
the cells to digest organic matter in their environment, breaking down large
molecules into smaller ones. The cells then absorb the nutrient molecules
through their cell membranes. Because the actual digestive process takes
place outside the organism's body, it is called extracellular digestion. A
similar type of food breakdown takes place in an animal's hollow gut." (p.
470, Postlethwait and Hopson, 1995)
All fungi are
chemoheterotrophic. They secrete hydrolytic
enzymes, which break down organic
polymers (polysaccharides and
proteins) into simpler organic compounds (monosaccharides or amino acids)
which they can absorb through their cell walls.
Habitat
Wherever adequate moisture, temperature, and organic
substrates are available, moulds are present. Although we normally think of
moulds as growing in warm, moist areas, many species occur in habitats that
are cold, periodically arid, or otherwise seemingly inhospitable.
Fungi are frequently found among the microbiota of soil and aquatic
ecosystems. A major role of these fungi is decomposition of dead and
decaying organic matter. Some species of fungi have adapted to a parasitic
life style, causing disease in animals and plants.
Reproduction
Moulds reproduce by releasing millions of tiny spores.
Mould spores are like seeds which germinate to produce a new
mould colony when they land on a suitable place. Mould spores
need moisture to grow and are usually found in damp, poorly ventilated areas
of homes, such as bathrooms. You cannot see individual mould spores but you may be able
to see mould colonies: grey, green or black, cottony, fuzzy or powdery growths on damp surfaces.
Studies have shown that mould
spores are a big source of indoor air pollution.
Moulds and fungi produce and
release millions of spores small enough to be air-, water-, or insect-borne.
They can also produce toxic compounds known as mycotoxins. Spores and
mycotoxins can have negative effects on human health including allergic
reactions, asthma and other respiratory problems.
Biologists who specialize in mould estimate that the
total number of different mould species ranges from over 100,000 to as many
as a million mould species.
Because moulds, mould spores, and mould toxins
often have a very adverse effects on humans, it is interesting and important
to note that only about 200 species of mould have been subject to medical
studies to determine a particular mould's health effects on people.
But even if most species have not yet been medically
studied, humans should minimize the amount of any kind of mould growing
inside their living quarters or their work place. The U.S. Environmental
Protection Agency warns that ANY mould in elevated levels in the indoor
environment can cause serious health problems.
Dimorphic fungi
Dimorphic organisms existing or occur in two distinct
forms. Dimorphic fungi grow as filamentous moulds at 25-30° and also as
yeast-like cells at 35-37° (the human body temperature). Commonly considered
dimorphic are:
Thermally dimorphic fungi can be dangerous to culture in
routine microbiology laboratory settings. The first known human case of P. marneffei
infection, in 1959, was the person who identified and christened
the fungus, G. Ségrétain. He accidentally inoculated himself with the fungus
by a needle when transfering the organism to a hamster.
An HIV-positive Congolese physician was also infected with P. marneffei
at
the Pasteur Institute after attending a course in tropical microbiology. The
organism was not handled directly by the patient, but by other students and
laboratory workers in the same building.
Asymptomatic infections can occur in healthy individuals. One study reported
serologic evidence of subclinical infection in two laboratory technicians.
The likely route of infection in most cases is inhalation of P. marneffei
spores.
Some laboratories recommend transferring young mould
colonies from petri dishes to slants as soon as they appear, limiting the
chance of Coccidioides arthrospore formation and laboratory worker exposure
should C. immitis be cultured. References
OSU Mansfield - Fungi |
