Mold Bacteria Consulting Laboratory, British Columbia, Alberta

Factors that affect the growth of moulds

The major factors affecting growth of mould are nutrients, temperature, light, aeration, pH and water activity.

Nutrients
Nutrient requirements for moulds may vary from mould to mould. Some moulds may thrive well on substrates with high sugar or salt content. Some may prefer simple sugars while others have the ability to utilize complex sugars.

Temperature
The majority of moulds are mesophilic, i.e., they can grow at temperatures within the range of 10-35°C. Optimum temperatures for growth may range between 15 and 30°C. However, some moulds such as Chaetomium thermophilum and Penicillium dupontii are thermophilic, i.e., they can grow at 45°C or higher and fail to grow below 20°C. A few moulds are psychrophilic and are unable to grow above 20°C. A significant number are psychrotolerant and are able to grow both at freezing point and at room temperature.

Light
Many moulds species grow well in the dark, but some prefer daylight or alternate light and darkness for them to produce spores.

Aeration
Nearly all moulds require air to grow.

pH.
Moulds differ in their pH requirements. Most will grow well over the pH range 3-7. Some such as Aspergillus niger and Penicillium funiculosum can grow at pH 2 and below.

Water activity
All moulds require moisture for growth but the amount required varies widely. Moulds that are capable of growing at very low water activity are referred to as xerophiles, for examples Eurotium species and Wallemia sebi. Those that are capable of growing at very high water activity are referred to as hydrophilic, e.g., Stachybotrys, Chaetomium and Ulocladium.

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