The fuzz spoiling your bread also gave us penicillin, soy sauce and Brie
Mould is not a single kind of organism but a growth habit shared by thousands of fungal species. The same threads that rot fruit also ferment soy sauce, ripen blue cheese, protect salami and yield drugs from penicillin to cyclosporine, the medicine that stops bodies rejecting transplanted organs.
What looks like fluff is a mycelium: a mesh of branching, tube-shaped filaments called hyphae, normally transparent, that together count as one organism. Growth happens only at the tips, where the fungus absorbs food and pushes forward through it. The dusty colours come from spores, the tiny units molds release in huge numbers to spread. Some spores are light and water-repellent enough to drift on the wind for long periods, and darkly pigmented walls help them survive ultraviolet light.
Molds are scattered across fungal groups such as Ascomycota and Zygomycota rather than forming one family. Unlike plants they cannot photosynthesise; they digest the material they sit on, and all of them need moisture, though xerophilic species cope with salty or sugary food where water activity falls below 0.85. Few can start growing at 4 °C or colder, which is why fridges are set around that mark.
Kitchens have harnessed them for centuries. In eastern Asia, koji molds such as Aspergillus oryzae ferment soybeans and wheat into soy sauce and turn rice starch into sugar for sake. Penicillium species ripen Brie and blue cheese, Penicillium nalgiovense forms the white bloom on some dry-cured sausages, and Rhizopus oryzae makes tempeh. Medicine owes them even more. Alexander Fleming's chance find of penicillin came from a Penicillium mold, although he could not produce enough of the compound to treat patients; an Oxford team including Howard Florey and Ernst Chain later concentrated it. Lovastatin, a cholesterol drug, comes from Aspergillus terreus.
The flip side is spoilage, property damage and illness. Heavy concentrations of spores indoors can trigger allergies and breathing trouble, and some species make mycotoxins that are dangerous when eaten in stored food. Stachybotrys chartarum is often called toxic mold, but research on the wider health effects of household mold has not reached firm conclusions.
Source: Mold
