Mould is a familiar, ever present form of fungus. It is estimated that there may be 1.5 million species of fungus, with 69000 described species. Visible fungus includes mushrooms, yeast, mould, mildew, puffballs and bracket fungi. Fungus accounts for approximately one quarter of the planet’s biomass. Unlike plants, which can produce their own food through photosynthesis, fungi absorb nutrients from other dead and living organic matter. There are numerous species of mould, which have a wide variety of characteristics and colours.

Mould reproduces by spreading microscopic spores. The spores of mould are always present in the air and on surfaces and can tolerate a wide range of conditions. They float in the air and can travel between countries and over oceans relatively quickly and may survive up to forty years before hatching when conditions are suitable. Ideal conditions for many mould species is relative humidity above 60%, temperatures between 10-32 degrees C and pH 3-8 and when these occur and damp organic material is present the mould reproduces rapidly. Huge colonies visible to the human eye may form quickly.

Mould spores are like minute floating eggs, which contain DNA within a hardened case. When these float into a dry surface they rebound back into the air, but when they float onto a wet surface they grip on and stick to the surface. The spore opens and a single organism emerges, the body grows a hyphae or arm, this hyphae grows another, then another until a huge network of hyphae are grown. The hyphae excrete digestive enzymes, which can break down complex organic material; the nutrients are absorbed by the hyphae and transported back to the central body. The nutrients may contain toxins, which the mould expels by spraying out aerosols such as carbon dioxide, alcohols etc and it is this process which produces the musty smell associated with mould and in extreme cases may contribute to Sick Building Syndrome.

Moulds are usually regarded as an unavoidable nuisance to humans but they are also utilised by humans for their benefit. Cultured moulds are used in a wide variety of food production eg an edible mould, Penicillium roqueforti is used to produce blue veined cheeses such Stilton and Roquefort. One of the most famous developments in relation to the use of mould, was the discovery that a species of mould belonging to the Penicillium genus inhibited bacterial growth, this led to the development of the antibiotic drug called Penicillin. Since then other mould based drugs such as the immunosuppressant cyclosporine have been developed.

It is often forgotten that mould plays a key role in the decomposition, degradation and recycling of nutrients by changing them from complex materials to simpler substances, which are then available to be released back into the environment.

We may not like mould but we could not live without it.

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