Aspergillus

NCBI:
Taxonomy
Genome

Aspergillus flavus (green mold). Dennis Kunkel Microscopy, Inc.

Classification

Higher order taxa:

Eukaryota; Fungi/Metazoa group; Fungi; Ascomycota; Pezizomycotina; Eurotiomycetes; Eurotiales; Trichocomaceae; mitosporic Trichomaceae

Species:

Aspergillus flavus, Aspergillus terreus, Aspergillus awamori

Description and Significance

Aspergillus is a member of the phylum [../ascomycota/ascomycota.html Ascomycota]. There are over 185 known species, about 20 of which are known to be harmfu to humans and other animals. The most infamous species of this genus is Aspergillus flavus, which produces aflatoxin. Aflatoxin is a contaminant of nuts and grain. It is both a toxin and a carcinogen. Aspergillus carbonarius and Aspergillus ochraceus produce the toxin ochratoxin A (OTA), which contaminates grapes and coffee.

A. fumigatus and A. niger are also extremely dangerous pathogens, causing aspergillosis. Although most of these organisms only cause severe illness in immunocompromised individuals, even otherwise healthy people may become infected; aspergillosis is often fatal. These illnesses are common among people who work in the farming industry, and are considered an occupational hazard. In addition, the diseases they cause, such as invasive pulmonary aspergillosis, are difficult to diagnose. Another ailment, allergic bronchopulmonary aspergillosis (ABPA), is a hypersensitivity disorder. It typically occurs in people with asthma or cystic fibrosis. Other diseases include: chronic necrotizing pulmonary aspergillosis, and allergic fungal sinusitis. These pathogens can attack any part of the body, from the sinuses to the lungs to the kidneys. Two Aspergillus species, A. flavus and A. parasiticus, are known to produce toxins only at acidic levels of pH. However, a West African strain of A. flavus actually produces less. In 2001, the Aspergillus Trust charity was formed to raise awarness for these diseases and support patients who are suffering from Aspergillus-related illnesses.

Genome Structure

There is not yet a major body of research completed on the genome structure of Aspergillus species.

Cell Structure and Metabolism

Lung infected with Aspergilloma.
Cornell University Medical College

While species vary in color, size, and growth rate, microscopic characteristics are fairly uniform across Aspergillus species. For example, all have hyphae that are septate and hyaline. Hyphae and conidia are separate. As is the case with other members of [../ascomycota/ascomycota.html Ascomycota], Aspergillus produces asci within ascocarps. Aspergillus gets its name from its shape. There is a vesicle in the shape of a circle, with filamentous extensions growing out from it. This resembles the shape of an aspergillum, a device used for sprinkling holy water.

As a pathogenic, opportunistic organism, Aspergillus species obtain nutrients from a host. Non-pathogenic species, or those that have not yet found a host, obtain nutrients from soil, plant detritus, or wood.

Like other members of [../ascomycota/ascomycota.html Ascomycota], Aspergillus species can reproduce both sexually and asexually, although asexual reproduction seems to be the most common.

Ecology

Aspergillus can be found almost anywhere, including soil, plant debris, wood, and both outdoor and indoor air. In addition, they are extremely resilient and occur in high numbers. Species are found in environments all over the world, though they occur most frequently during autumn and winter in the Northern Hemisphere.

Aspergillus species are sometimes used in the manufacturing of household foods. Many common products, such as soy sauce, chocolate, soft drinks, vitamins, black tea, and fruit juice undergo a fermentation process with Aspergillus. A. niger is used to make citric acid. Unfortunately, this may have negative effects on immunocompromised individuals, who are advised to stay away from food products which have undergone this process.

A non-carcinogenic, aflatoxin-free strain of Aspergillus flavus, A. flavus AF36, is used as a pesticide to kill aflatoxin-producing fungi. AF36 is applied to the soil and germinates, out-competing aflatoxin-producing strains of A. flavus.