Aspergillus spores are common components of aerosols where they drift on air currents, dispersing themselves both short and long distances depending on environmental conditions. When the spores come in contact with a solid or liquid surface, they are deposited and if conditions of moisture are right, they germinate. The ability to disperse globally in air currents and to grow almost anywhere when appropriate food and water are available means that 'ubiquitous' is among the most common adjectives used to describe these moulds.
One of the defining characteristics of the entire fungal kingdom is its distinctive nutritional strategy. These organisms secrete acids and enzymes into the surrounding environment, breaking down polymeric molecules down into simpler ones that are then absorbed back into the fungal cell. Fungi, like animals, are heterotrophic. While animals eat their food and then digest it, fungi first digest their food and then 'eat' it. Gaining access to nutrients is aided by mechanical forces whereby fungal hyphal tips grow into and through their food substrates. Species of
Aspergillus are typical examples of the fungal life style. They are most often found in terrestrial habitats and are commonly isolated from soil and associated plant litter. The decomposition process carried out by these moulds is important in driving natural cycling of chemical elements, particularly in the carbon cycle where they contribute to replenishment of the supply of carbon dioxide and other inorganic compounds.
In the ecosystem, different substrates are attacked at different rates by consortia of organisms from different kingdoms.
Aspergillus and other moulds play an important role in these consortia because they are adept at recycling starches, hemicelluloses, celluloses, pectins and other sugar polymers. Some aspergilli are capable of degrading more refractory compounds such as fats, oils, chitin, and keratin. Maximum decomposition occurs when there is sufficient nitrogen, phosphorus and other essential inorganic nutrients. Fungi also provide food for many soil organisms.
For
Aspergillus the process of degradation is the means of obtaining nutrients. When these moulds degrade human-made substrates, the process usually is called biodeterioration. Both paper and textiles (cotton, jute, and linen) are particularly vulnerable to
Aspergillus degradation. Our artistic heritage is also subject to
Aspergillus assault. To give but one example, after Florence in Italy flooded in 1969, 74% of the isolates from a damaged Ghirlandaio fresco in the Ognissanti church were
Aspergillus versicolor.
Suggested reading: Microbial Biodegradation: Genomics and Molecular BiologySimilarly, foods utilized by humans and our domestic animals are good nutritional sources for
Aspergillus. Words like 'decay,' 'rot' and 'spoilage' are used to describe such fungal utilization of our foodstuffs, which can occur in the field prior to harvest, during storage, and after commercial processing or cooking in the home. Although foods with an acidic pH, dried foods, and those with a high concentration of sugars such as jams and jellies normally do not support microbial growth many members of the
A. glaucus group (
Eurotium) are able to grow at low water activity. These species even have been isolated from salted, dry fish. In the same way, grains, nuts and spices, all of which have relatively low amounts of water, regularly are attacked by moderately xerophilic species of
Aspergillus.
Suggested reading: Foodborne Pathogens: Microbiology and Molecular BiologyAdapted from
An Overview of the Genus Aspergillus by
Joan W. Bennett writing in
Aspergillus: Molecular Biology and GenomicsFurther readingLabels: Aspergillus ecology, Aspergillus physiology