The colloquial term “mold” is applied to a large and taxonomically diverse number of fungal species where their growth results in a “moldy” appearance of objects, especially food. The objects become discolored by a layer of fungal growth. Molds are fungi that grow in the form of multicellular filaments called hyphae. A connected network of these tubular branching hyphae, called a mycelium, is considered a single organism. Cross-walls (septa) may delimit connected compartments along the hyphae, each containing one or multiple, genetically identical nuclei. In contrast, fungi that can adopt a single celled growth habit are called yeasts.
Molds are considered to be microbes and 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.
Molds reproduce through small spores. Mold spores may remain airborne indefinitely, may cling to clothing or fur or may be able to survive extremes of temperature and pressure.
Where are molds found?
Although molds grow on dead organic matter everywhere in nature, their presence is visible to the unaided eye only when mold colonies grow. A mold colony does not consist of discrete organisms but of an interconnected network of hyphae called a mycelium. Nutrients and in some cases organelles may be transported throughout the mycelium. In artificial environments such as 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.
Few molds can begin growing at 4 °C (39 °F), the temperature within a typical refrigerator, or less. 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 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.
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