A driving factor in building construction is the continuous pressure to save time and money. These pressures usually result in gradual shifts in how buildings are made. Beginning in the late 1940’s, these gradual shifts have resulted in better and better conditions for fungal growth. This is perhaps nowhere more apparent than in schools. In the 1940’s and before, schools were built of stone, brick and marble. Floors (at least in urban schools) were either hardwood (nutrient poor for most fungi) or marble. Walls were tile or plaster. Windows were operable, and the buildings were not tight, resulting in plenty of ventilation. Now, we have floors covered with carpeting, which holds water and nutrients. Walls are built of gypsum board that is filled with nutrients. Windows are sealed, which requires costly energy to ventilate, leading to low ventilation rates and accumulation of water. We can live with these changes if we understand how fungi grow so that we can efficiently limit their growth.
Molds are spread by spores, each of which contains all the genetic material to make a new colony. While traveling through the air or on your clothes or other carriers, they are dormant, and chemical reactions in the spore are going on very slowly. When a spore lands on a dry surface, it remains dormant and will eventually die. If water is present, it is drawn into the spore by a process known as osmosis. With the water are dissolved nutrients. The concentration and type of nutrients depends on the material on which the spore lands. If there is enough water and if the nutrient content is appropriate, then the spore will swell, and a germ tube will appear. The germ tube releases enzymes (catalysts) that help in the digestion of insoluble nutrients (e.g., starch, cellulose, etc). If the appropriate nutrient is available, the enzymes will break it down into soluble fragments, which will be absorbed into the germ tube, stimulating continued growth. The size the colony reaches depends on both environmental conditions and the genetics of the fungus. Given ideal conditions, it will grow to its genetically pre-determined size as long as sufficient water and nutrients are available and the temperature is appropriate or until the colony encounters competition from other fungi. If the proper nutrients are not available, or if the water supply disappears, then the germ tube and the spore die. Given proper conditions, fungi will generally grow vegetatively until some environmental variable becomes limiting. Water or nutrients may be depleted, or temperature or lighting conditions could change. When these changes occur, fungi stop vegetative growth and may begin to produce new spores.
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