From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article is about the fungi known as mold. Slime molds and water molds are not fungi and are discussed in separate articles. For other uses, see Mold (disambiguation).
Mold growing on a clementine
Spinellus fusiger growing on the mushroom Mycena haematopus
Moldy tomatoes
Mold on dried Hibiscus sabdariffa

A mold (US) or mould (UK / NZ / AU / ZA / CA) is a fungus that grows in the form of multicellular filaments called hyphae.[1][2] In contrast, fungi that can adopt a single celled growth habit are called yeasts.

Molds are a large and taxonomically diverse number of fungal species where the growth of hyphae results in discoloration and a fuzzy appearance, especially on food.[3] The network of these tubular branching hyphae, called a mycelium, is considered a single organism. The hyphae are generally transparent, so the mycelium appears like very fine, fluffy white threads over the surface. Cross-walls (septa) may delimit connected compartments along the hyphae, each containing one or multiple, genetically identical nuclei. The dusty texture of many molds is caused by profuse production of asexual spores (conidia) formed by differentiation at the ends of hyphae. The mode of formation and shape of these spores is traditionally used to classify molds.[4] Many of these spores are colored, making the fungus much more obvious to the human eye at this stage in its life-cycle.




There are thousands of known species of molds, which have diverse life-styles including saprotrophs, mesophiles, psychrophiles and thermophiles and a very few opportunistic pathogens of humans.[6] They all require moisture for growth and some live in aquatic environments. Like all fungi, molds derive energy not through photosynthesis but from the organic matter on which they live, utilising heterotrophy. 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 synthesise mycotoxins and siderophores which, together with lytic enzymes, inhibit the growth of competing microorganisms. Molds can also grow on stored food for animals and humans, making the food unpalatable or toxic and are thus a major source of food losses and illness.[7] Many strategies for food preservation (salting, pickling, jams, bottling, freezing, drying) are to prevent or slow mold growth as well as growth of other microbes.

Molds reproduce by producing large numbers of small spores,[6] 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. Some molds produce small, hydrophobic spores that are adapted for wind dispersal and may remain airborne for long periods; in some the cell walls are darkly pigmented, providing resistance to damage by ultraviolet radiation. Other mold spores have slimy sheaths and are more suited to water dispersal. Mold spores are often spherical or ovoid single cells, but can be multicellular and variously shaped. Spores may cling to clothing or fur; some are able to survive extremes of temperature and pressure.


Few molds can begin growing at temperatures of 4 °C (39 °F) or below, so food is typically refrigerated at this temperature. When conditions do not enable growth to take place, molds may remain alive in a dormant state depending on the species, within a large range of temperatures. 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.[8]:22

Xerophilic molds are able to grow in relatively dry, salty, or sugary environments, where water activity (aw) is less than 0.85; other molds need more moisture.[9]

Common molds[edit]

Food production[edit]

The Kōji (?) molds are a group of Aspergillus species, notably Aspergillus oryzae, and secondarily A. sojae, 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. Koji molds break down the starch in rice, barley, sweet potatoes, etc., a process called saccharification, in the production of sake, shōchū and other distilled spirits. Koji molds are also used in the preparation of Katsuobushi.

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.[10] A study has shown that 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.[11]

Some sausages, such as salami, incorporate starter cultures of molds [12] to improve flavour and reduce bacterial spoilage during curing. Penicillium nalgiovense, for example, may appear as a powdery white coating on some varieties of dry-cured sausage.

Other molds that have been used in food production include:

Pharmaceuticals from molds[edit]

Alexander Fleming's accidental discovery of the antibiotic penicillin involved a Penicillium mold called Penicillium notatum (although the species identity is disputed as possibly being Penicillium chrysogenum or Penicillium rubens).[13] Fleming continued to investigate Penicillin, showing that it could inhibit various types of bacteria found in infections and other ailments, but was unable produce the compound in large enough amounts necessary for production of a medicine.[14] His work was expanded by a team at Oxford University; Clutterbuck, Lovell, and Raistrick, who began to work on the problem in 1931. This team was also unable to produce the pure compound in any large amount, and found that the purification process diminished its effectiveness and negated the anti-bacterial properties it had.[14]

Howard Florey, Ernst Chain, Norman Heatley, Edward Abraham, also all at Oxford, continued the work.[14] They enhanced and developed the concentration technique by using organic solutions rather than water, and created the "Oxford Unit" to measure penicillin concentration within a solution. They managed to purify the solution, increasing it's concentration by 45-50 times, but found that a higher concentration was possible. Experiments were conducted and the results published in 1941, though the quantities of Penicillin produced were not always high enough for the treatments required.[14] As this was during the Second World War, Florey sought USA Government involvement. With research teams in the UK and some in the US, industrial-scale production of crystallised penicillin was developed during 1941-1944 by the USDA and by Pfizer.[13][15]

Several statin cholesterol-lowering drugs (such as Lovastatin, from Aspergillus terreus) are derived from molds.[16]


Health effects[edit]

Main article: Mold health issues


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 home exposure, may be particularly harmful. Research on the health impacts of mold has not been conclusive.[17] The term "toxic mold" refers to molds that produce mycotoxins, such as Stachybotrys chartarum, and not to all molds in general.[18]


Molds can also pose a hazard to human and animal health when they are consumed following the growth of certain mold species in stored food. Some species produce toxic secondary metabolites, collectively termed mycotoxins including aflatoxins, ochratoxins, fumonisins, trichothecenes, citrinin, and patulin. These toxic properties may be used for the benefit of humans when the toxicity is directed against other organisms; for example, penicillin adversely affects the growth of Gram-positive bacteria (e.g. Clostridium species), certain spirochetes and certain fungi.[19]

Growth in buildings and homes[edit]

Mold growth in buildings can lead to a variety of health problems. 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.[18] Removal of affected materials after the source of moisture has been reduced and/or eliminated may be necessary for remediation.

See also[edit]


  1. ^ a b Moore D; Robson GD; Trinci APJ (editors). (2011). 21st Century Guidebook to Fungi (1st ed.). Cambridge University Press. ISBN 978-0521186957. 
  3. ^ Morgan, Mike. "Moulds". Microscopy UK. Retrieved 26 June 2012. 
  4. ^ Chiba University, Japan. "Fungus and Actinomycetes Gallery". Chiba University Medical Mycology Research Center. Retrieved 26 June 2012. 
  6. ^ a b Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 633–8. ISBN 0-8385-8529-9. 
  7. ^ Wareing, Peter. "The Fungal Infection of Agricultural Produce and the Production of Mycotoxins". European Mycotoxins Awareness Network. Retrieved 3 August 2013. 
  8. ^ Malloch, D. (1981). Moulds : their isolation, cultivation and identification. Toronto Canada: Univ. of Toronto Press. ISBN 0-8020-2418-1. 
  9. ^ Pitt JI, Hocking AD (2009). Fungi and Food Spoilage. London: Springer. doi:10.1007/978-0-387-92207-2_9. 
  10. ^ "Red yeast rice (Monascus purpureus)". Mayo Clinic. 2009-09-01. Retrieved 2010-02-01. 
  11. ^ "Study: Red Rice Yeast Helps Cut Bad Cholesterol". National Public Radio. 2008-07-01. Retrieved 2010-02-01. 
  12. ^ L. H. Stahnke, L. O. Sunesen; Stahnke, L.H (November 2003). "Mould starter cultures for dry sausages—selection, application and effects". Meat Science 65 (3): 935–948. doi:10.1016/S0309-1740(02)00281-4. PMID 22063673. Retrieved 2008-06-06. 
  13. ^ a b "The Nobel Prize website". Retrieved 27 June 2012. 
  14. ^ a b c d "Award Ceremony Speech". Nobel Prizes and Laureates. Nobel Media. Retrieved 26 May 2014. 
  15. ^ ACS Chemistry for Life. "The discovery of penicillin". Retrieved 27 June 2012. [dead link]
  16. ^ Wikipedia. "Statins". Wikipedia. Retrieved 13 June 2012. 
  17. ^ Money, Nicholas (2004). Carpet Monsters and Killer Spores: A Natural History of Toxic Mold. Oxford, UK: Oxford University Press. p. 178. ISBN 0-19-517227-2. 
  18. ^ a b Indoor Environmental Quality: Dampness and Mold in Buildings. National Institute for Occupational Safety and Health. August 1, 2008.
  19. ^ Saunders Comprehensive Veterinary Dictionary, Blood and Studdert, 1999

External links[edit]