Mould

Mould, fuzzy, cobweb-like growth produced on organic matter by several types of fungi. The terms mould and mildew are commonly used interchangeably, although mould is often applied to black, blue, green, and red fungal growths, and mildew to whitish ones.

Black bread mould, Aspergillus niger, one of the most familiar moulds, 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 root-like hyphae, called rhizoids, which penetrate the organic material, secreting enzymes and absorbing water and digested sugars and starches. Other clusters of hyphae called sporangiophores then reach upwards, forming sporangia (knob-like spore cases), which bear the particular colour of the mould species. On ripening, the sporangia break open and the windborne spores land elsewhere to reproduce asexually.

Some moulds 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.

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