Mold (fungi)

Mold (fungi), fuzzy, cobweblike growth produced on organic matter by several types of fungi. Mold and mildew are commonly used interchangeably, although mold is often applied to black, blue, green, and red fungal growths, and mildew to whitish growths.

Black bread mold, Aspergillus niger, one of the most familiar molds, begins as a microscopic, airborne spore that germinates on contact with the moist surface of nonliving organic matter. It spreads rapidly, forming the mycelium (fungal body), which is made up of a fine network of filaments (hyphae). The mycelium produces other clusters of rootlike hyphae, called rhizoids, which penetrate the organic material, secreting enzymes and absorbing water and the digested sugars and starches. Other clusters of hyphae called sporangiophores then reach upward, forming sporangia (knoblike spore cases), which bear the particular color of the mold species. Upon ripening, the sporangia break open and the windborne spores land elsewhere to reproduce asexually.

Some molds also reproduce sexually through conjugation of gamete cells by the joining of two specialized hyphae. The resulting zygote matures into a zygospore that germinates after a dormant period.

Molds thrive on a great many organic substances and, provided with sufficient moisture, they rapidly disintegrate wood, paper, and leather. In fruit the enzymes penetrate well behind the area of the visible growths to damage the fruit. Besides being destructive, however, molds also have many industrial uses, such as in the fermentation of organic acids and cheeses. Camembert and Roquefort cheeses, for example, gain their particular flavors from the enzymes of Penicillium camemberti and P. roqueforti, respectively. Penicillin, a product of the green mold P. notatum, revolutionized antibiotic drugs after its discovery in 1929, and the red bread mold Neurospora is an important tool in genetic experiments.