Factors Affecting Fungal Growth Indoors

Many environmental parameters can influence fungal growth indoors. Some are biotic factors, and others are physical and chemical, or abiotic factors. Biotic factors include the presence of fungal propagules or spores, viability of spores, the nature of the fungal species, and competing fungi and other organisms.

Sampling and Analysis of Indoor Microorganisms, Edited by Chin S. Yang and Patricia A. Heinsohn Copyright © 2007 John Wiley & Sons, Inc.

Abiotic factors include nutrients, temperature, moisture, pH, oxygen and carbon dioxide, and light. Fungi are not photosynthetic and require a wide range of nutrients, including carbon, nitrogen, sulfur, and various macro- and micronutrients for their survival and growth. Most fungi, including anamorphilic ones, and yeasts are little impacted in their growth by hydrogen ions, as measured in pH.3 Fungi are generally considered mildly acidophilic, with a preferred pH of slightly acidic at pH ~5. Most fungi found in food and other substrates grew in a wide pH range of 3-8.3,4 Some fungi, such as Aspergillus niger and Penicillium italicum, are able to grow at a pH as low as 2.3 The pH levels in the substrates may affect competition between fungi and other microbes, such as bacteria. However, bacteria may outperform fungi at near-neutral pH and higher.5 On the other hand, most building materials are within the range cited by Wheeler et al.4 The impact of pH on indoor fungal growth is generally considered insignificant.

For practical purposes, moisture, nutrients, and temperature and their interactions with fungi indoors are discussed in detail below because they are the most important abiotic factors in determining whether fungal spores may germinate and grow. The impact of other environmental parameters is also discussed.

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