Mold

This article is about the fungi known as molds. Slime molds and water molds are not fungi and are discussed in separate articles. For other uses, see Mold (disambiguation).

Molds (or moulds; see spelling differences) are fungi that grow in the form of multicellular filaments called hyphae. In contrast, microscopic fungi that grow as single cells are called yeasts. A connected network of these tubular branching hyphae has multiple, genetically identical nuclei and is considered a single organism, referred to as a colony.

Molds do not form a specific taxonomic or phylogenetic grouping, but can be found in the divisions Zygomycota, Deuteromycota and Ascomycota. Some molds cause disease or food spoilage, others play an important role in biodegradation or in the production of various foods, beverages, antibiotics and enzymes.

Biology

There are thousands of known species of molds which include opportunistic pathogens, saprotrophs, aquatic species, and thermophiles. Like all fungi, molds derive energy not through photosynthesis but from the organic matter in which they live. Typically, molds secrete hydrolytic enzymes, mainly from the hyphal tips. These enzymes degrade complex biopolymers such as starch, cellulose and lignin into simpler substances which can be absorbed by 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, which may contain a single nucleus or be multinucleate. Mold spores can be asexual (the products of mitosis) or sexual (the products of meiosis); many species can produce both types. Mold spores may remain airborne indefinitely, may cling to clothing or fur, or may be able to survive extremes of temperature and pressure. I LIKE CHICKEN 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 like buildings, 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 other surfaces.

Many molds can begin growing at 4 °C (39 °F), the temperature within a typical refrigerator, or less. When conditions do not enable growth, molds may remain alive in a dormant state depending on the species, within a large range of temperatures before they die. The many different mold species vary enormously in their tolerance to temperature and humidity extremes. Certain molds can survive harsh conditions such as the snow-covered soils of Antarctica, refrigeration, highly acidic solvents, anti-bacterial soap and even petroleum products such as jet fuel.

Xerophilic molds use the humidity in the air as their only water source; other molds need more moisture. Mold has a musty odor.

Common molds

• Acremonium
• Aspergillus
• Cladosporium
• Fusarium
• Mucor
• Penicillium
• Rhizopus
• Stachybotrys
• Trichoderma

Food production

Cultured molds are used in the production of foods, including:

• cheese (Penicillium spp.)
• tempeh (Rhizopus oligosporus)
• oncom (Neurospora sitophila)
• Quorn (Fusarium venenatum)
• some sausages
• soy sauce

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.

Red rice yeast is a product of the mold Monascus purpureus grown on rice, and is common in Asian diets. The yeast contains several compounds collectively known as monacolins, which are known to inhibit cholesterol synthesis. According to a study published in the journal Mayo Clinic Proceedings by Dr. David Becker, red rice yeast used as a dietary supplement, combined with fish oil and healthy lifestyle changes, may help reduce "bad" cholesterol as effectively as certain commercial statin drugs.

Drug creation

Alexander Fleming's famous discovery of the antibiotic penicillin involved the mold Penicillium chrysogenum.

Several cholesterol-lowering drugs (such as Lovastatin, from Aspergillus terreus) are derived from molds.

The immunosuppressant drug cyclosporine, used to suppress the rejection of transplanted organs, is derived from the mold Tolypocladium inflatum.

Health effects

Main article: Mold health issues

Molds are ubiquitous in nature, and mold spores are a common component of household and workplace dust. However, when mold spores are present in large quantities, they can present a health hazard to humans, potentially causing allergic reactions and respiratory problems.

Some molds also produce mycotoxins that can pose serious health risks to humans and animals. Some studies claim that exposure to high levels of mycotoxins can lead to neurological problems and in some cases death. Prolonged exposure, e.g. daily workplace exposure, may be particularly harmful. Research on the health effects of mold has not been conclusive. The term "toxic mold" refers to molds that produce mycotoxins, such as Stachybotrys chartarum, and not to all molds in general.

Mold in the home can usually be found in damp, dark or steam filled areas e.g. bathroom or kitchen, cluttered storage areas, recently flooded areas, basement areas, plumbing spaces, areas with poor ventilation and outdoors in humid environments. Symptoms caused by mold allergy are watery, itchy eyes, a chronic cough, headaches or migraines, difficulty breathing, rashes, tiredness, sinus problems, nasal blockage and frequent sneezing.

Growth in buildings and homes

Main articles: Mold growth, assessment, and remediation and Indoor air quality

Mold growth in buildings can lead to a variety of health issues. Various practices can be followed to mitigate mold issues in buildings, the most important of which is to reduce moisture levels that can facilitate mold growth. Removal of affected materials after the source of moisture has been reduced and/or eliminated may be necessary for remediation.

Gallery

• 
  Bread mold is one of the most common types of mold, and can cover a loaf of bread in less than three days.
• 
  Mold covering a decaying peach over a period of six days. The frames were taken approximately 12 hours apart. There are 12 frames of changes.
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  Moldy nectarines that were in a refrigerator. The nectarine with black mold is also affecting the nectarine underneath.
• 
  A bowl of moldy strawberries after being left in a room for several days.
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  Mold cultured from dust shaken from an automotive cabin air filter. 10× objective, 15× eyepiece; each numbered tick is 122 µM.
• 
  Mold grown from a nasal mucus sample.  10× objective, 15× eyepiece; each numbered tick is 122 µM.
• 
  Mildew from a wooden soap holder.  Numbered ticks are 11 µM apart.
• 
  Mildew growing on a plastic shower curtain.  10× objective, 15× eyepiece; each numbered tick is 122 µM.
• 
  Mycelium of unidentified mold. This image covers a one-millimeter square.
• 
  Another mycelium, of another mold.  Numbered ticks are 230 µM apart.
• 
  Stilton cheese contains edible mold.
• A moldy tomato
  A moldy tomato
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  Moldy bread
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  Detailed picture of mold on tomato
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  Moldy peach
• 
  Moldy coffee
• 
  Mold on rice

See also

• Bioaerosol
• Decay
• Medicinal mushrooms
• Mildew
• Mold mite
• Mycorrhiza
• Oomycete

External links

• The EPA's guide to mold