Difference between revisions of "Aspergillus"

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Revision as of 13:31, 22 August 2006

A Microbial Biorealm page on the genus Aspergillus

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, A. terreus, A. awamori

NCBI: Taxonomy Genome

Description and Significance

Aspergillus is a member of the phylum Ascomycota. There are over 185 known species, about 20 of which are known to be harmful 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, 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, Aspergillus species can reproduce both sexually and asexually, although asexual reproduction seems to be the more common.

Ecology

Aspergillus versicolor (black mold). Dennis Kunkel Microscopy, Inc.

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.

References

Aspergillus Trust.

Bacchus, Shanaz. "Aspergillus flavus strain AF36 (006456) Fact Sheet." 31 May 2005. Accessed 7 July 2005.

Dennis Kunkel Microscopy, Inc.

Doctor Fungus. "Aspergillus spp." Accessed 7 July 2005.

Ehrlich, KC, BG Montalbano, and PJ Cotty. "Divergent regulation of aflatoxin production at acidic pH by two Aspergillus strains." Mycopathologia. 2005 Jun;159(4):579-81.

Filler SG, Yeaman MR, and Sheppard DC. "Tumor Necrosis Factor Inhibition and Invasive Fungal Infections." Clinical infectious diseases: an official publication of the Infectious Diseases Society of America. 2005 Aug 1;41 Suppl 3:S208-S212.

Garnacho-Montero, José, Rosario Amaya-Villar, Carlos Ortiz-Leyba, Cristóbal León, Francisco Álvarez-Lerma, Juan Nolla-Salas, José R Iruretagoyena, and Fernando Barcenilla. "Isolation of Aspergillus spp. from the respiratory tract in critically ill patients: risk factors, clinical presentation and outcome." Critical Care. 2005;9(3):191-199.

Godwin, Thomas A. "Respiratory System." Cornell University Medical College. 26 July 1995. Accessed 7 July 2005.

Mold-Help.org. "Aspergillus." Accessed 6 July 2005.

Patino B, A Gonzales-Salgado, MA Gonzales-Jaen, and C Vazquez. "PCR detection assays for the ochratoxin-producing Aspergillus carbonarius and Aspergillus ochraceus species." International journal of food microbiology. 2005 Jun 17.

Porter, Caroline. "Aspergillus." Accessed 7 July 2005.

Public Health Agency of Canada. "Material Safety Data Sheet - Infectious Substances." 23 January 2001. Accessed 7 July 2005.

Taylor, John W., Joey Spatafora, and Mary Berbee. "Ascomycota." The Tree of Life Web Project. Accessed 6 July 2005.

Tillie-Leblond, I. and A.-B. Tonnel. "Allergic bronchopulmonary aspergillosis." Allergy 2005:60:1004–1013.

Volk, Tom. "Tom Volk's Fungus of the Month for February 1997." 1997. Accessed 7 July 2005.