MOLD

'Molds' (or 'moulds', see spelling differences) include all species of microscopic fungi that grow in the form of multicellular filaments, called hyphae. Brock Biology of Microorganisms, Madigan M; Martinko J (editors)., , , Prentice Hall, 2005, ISBN 0131443291 In contrast, microscopic fungi that grow as single cells are called yeasts. A connected network of these tubular branching hyphae has the same DNA and is considered a single organism, referred to as a colony or in more technical terms a mycelium.
Molds do not form a specific taxonomic or phylogenetic grouping, but can be found in the divisions ''Zygomycota'', ''Deuteromycota'' and ''Ascomycota''. Although some molds cause disease or food spoilage, others are useful for their role in biodegradation or in the production of various foods, beverages, antibiotics and enzymes.

Contents

Biology

Uses

Health effects

Growth in buildings

See also

References

Biology

There are thousands of known species of molds, which include opportunistic pathogens, exclusive saprotrophs, aquatic species and thermophiles. Sherris Medical Microbiology, Ryan KJ; Ray CG (editors), , , McGraw Hill, 2004, ISBN 0838585299 Like all fungi, molds derive energy not through photosynthesis but from the organic matter on which they live. Typically, molds secrete hydrolytic enzymes from predominantly the hyphal tips. These enzymes degrade complex biopolymers such as starch, cellulose and lignin into simpler substances which can enter the hyphae. In this way, molds play a major role in causing decomposition of organic material, enabling the recycling of nutrients throughout ecosystems. Many molds also secrete mycotoxins which, together with hydrolytic enzymes, inhibit the growth of competing microorganisms.
Molds reproduce through small spores. Mold spores can be asexual (the products of mitosis) or sexual (the products of meiosis), and many species can produce both types. They may contain a single nucleus or many. Some can remain airborne indefinitely, and many are able to survive extremes of temperature and pressure.
Although molds grow on dead organic matter everywhere in nature, their presence is only visible to the unaided eye when mold colonies grow. A mold colony does not comprise discrete organisms, but an interconnected network of hyphae called a mycelium. Nutrients and in some cases organelles may be transported throughout the mycelium. In artificial environments, humidity and temperature are often stable enough to foster the growth of mold colonies, commonly seen as a downy or furry coating growing on food or surfaces. Thus buildings, being stable environments, enable mold proliferation.
Some mold can begin growing at temperatures as low as 2°C. When conditions do not enable growth, molds can remain alive in a dormant state, within a large range of temperatures before they die. This explains how molds can survive harsh conditions such as containers in refrigerators or inside building structure cavities.
Xerophilic molds use the humidity in the air as their only water source; other molds need more moisture.

Uses

Stilton cheese contains edible mold.

Cultured molds are used in the production of foods including cheese (''Penicillium spp''), tempeh (''Rhizopus oligosporus''), quorn (''Fusarium venenatum''), the black tea pu-erh and some sausages.
The ''koji'' molds are a group of ''Aspergillus'' species, notably ''Aspergillus oryzae'', that have been cultured in eastern Asia for many centuries. They are used to ferment a soybean and wheat mixture to make soybean paste and soy sauce. They are also used to break down the starch in rice (saccharification) in the production of ''sake'' and other distilled spirits.
Other molds are cultivated for their ability to produce useful substances. ''Aspergillus niger'' is used in the production of citric acid, gluconic acid and many other compounds and enzymes. Alexander Fleming's famous discovery of the antibiotic penicillin involved the mold ''Penicillium notatum''.
The molds ''Neurospora crassa'' and ''Aspergillus nidulans'' are commonly used model organisms.

Health effects

Light micrograph of the hyphae and spores of the human pathogen ''Aspergillus fumigatus''

Some mycotoxins produced by molds are harmful to humans. Other mycotoxins cause immune system responses that vary considerably, depending on the individual. The duration of exposure is a key factor in triggering immune system response. Farm animals often die or suffer from mycotoxin poisoning. Mycotoxins resist decomposition from cooking, and remain in the food chain.
Mold spores can be allergenic. When inhaled, mold spores may germinate, attaching to cells along the respiratory tract and causing further problems in those with weak immune systems. One example is ''Stachybotrys chartarum'' which has been associated with sick building syndrome.
Infection by opportunistic pathogen molds such as ''Penicillium marneffei'' and ''Aspergillus fumigatus'' is a common cause of death among immunocompromised people, including AIDS patients.

Growth in buildings

Although this home suffered only minor exterior damage from Hurricane Katrina, small leaks and inadequate air flow permitted this mold infestation.

Both our indoor and outdoor environment have mold spores present. There is no such thing as a mold free environment in the Earth's biosphere.
Spores need three things to grow into mold:

★ Nutrients: Food for spores in an indoor environment is organic matter, often cellulose.

★ Moisture: Moisture is required to begin the decaying process caused by the mold.

★ Time: Mold growth begins between 24 hours and 10 days from the provision of the growing conditions. There is no way to date mold.
Mold colonies can grow inside building structures. The main problem with the presence of mold in buildings is the inhalation of mycotoxins. Molds may produce an identifiable smell. Growth is fostered by moisture. After a flood or major leak, mycotoxin levels are higher in the building even after it has dried out (source: CMHC).
Food sources for molds in buildings include cellulose-based materials, such as wood, cardboard, and the paper facing on both sides of drywall, and all other kinds of organic matter, such as soap, dust and fabrics. Carpet contains dust made of organic matter such as skin cells. If a house has mold, the moisture may be from the basement or crawl space, a leaking roof, or a leak in plumbing pipes behind the walls. Insufficient ventilation can further enable moisture build-up. The more people in a space, the more humidity builds up. This is from normal breathing and perspiring. Visible mold colonies may form where ventilation is poorest, and on perimeter walls, because they are coolest, thus closest to the dew point.
If there are mold problems in a house only during certain times of the year, then it is probably either too air-tight, or too drafty. Mold problems occur in airtight homes more frequently in the warmer months (when humidity reaches high levels inside the house, and moisture is trapped), and occur in drafty homes more frequently in the colder months (when warm air escapes from the living area into unconditioned space, and condenses). If a house is humidified artificially during the winter, this can create conditions favorable to mold. Moving air may prevent mold from growing since it has the same desiccating effect as lowering humidity.
There are many ways to prevent mold growth; see ventilation issues in houses.
In extreme cases of mold growth in buildings, it may be easier to condemn the building rather than clean the mold to safe levels; see Deutsche Bank Building.
Certain contractors are capable of repairing mold damage - usually by removing the affected areas and eliminating the cause of the excess moisture.
There are also cleaning companies that specialize in Fabric Restoration - a process by which mold and mold spores are removed from clothing to eliminate odor and prevent further mold growth and damage to the garments.

See also

★ Indoor air quality

★ Bioaerosol

★ Mildew

★ Mold assessment

★ Mold mite

★ Slime mould

★ Stachybotrys

★ Toxic mold

★ Oomycete

References