Fungal Growth Phases
From the time a spore or a hyphal fragment germinates to form a colony to the time the fungus dies, there are a number of growth phases. Although these phases have been determined under laboratory conditions, it is possible that the same occur in nature. In nature the duration of each phase would be determined by the environmental conditions including other competing micro-organisms.
- Lag phase
Once the growth conditions become favorable for the fungal propagules (i.e., viable spores or mycelial fragments) to germinate, new transport systems must be induced before growth commences. Thus growth starts slowly and accelerates gradually. This phase is referred to as the lag phase.
- Exponential or log phase
Exponential growth occurs only for a brief period as hyphae branches are initiated, and then the new hypha extends at a linear rate into in-colonized regions of substrate. The biomass of the growing fungus doubles per unit time. As long as the nutrients are in excess growth remains constant during the exponential phase.
- Stationary phase
As soon as the nutrients are depleted or toxic metabolites are produced growth slows down or is completely stopped. The biomass increases gradually or remains constant. During the stationary phase, hyphal growth stops and, in some molds, cell differentiation occurs, resulting in spore formation. During this process nutrients are transferred from the vegetative mycelium to the developing spores. The spores are dispersed by air movement to other areas of the building where they can start new mold growth once the conditions for growth are favorable.
- The death phase
During the death phase, the mycelium eventually dies off. The death phase is usually accompanied by breakdown of the mycelia through self-digestion. Some fungi form spores by fragmentation of the hyphae