Aspergillus flavus

Aspergillus Flavus
Scientific classification
Kingdom:	Fungi;
Phylum:	Ascomycota;
Class:	Eurotiomycetes;
Order:	Eurotiales;
Family:	Trichocomaceae;
Genus:	Aspergillus;
Species:	A. flavus;
Binomial name
	Aspergillus flavus;

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Description and significance

Aspergillus flavus is a filamentous fungus. It produces a mycotoxin called aflatoxin B₁. Aflatoxin B₁ is carcinogenic. It can cause liver damage in humans and animals. It is also one of the mycotoxins used as a biologcal weapon⁴. When crops are infected with A. Flavus their value decreases because of the exposure of the crop to aflatoxin.² Aspergillus Flavus is mainly a saprophyte, meaning it obtains its nutrients from dead or decaying material, but it can also be a pathogen to plants animals and humans.¹

Pathology

A. Flavus is an opportunistic pathogen, which allows it to infect animals, humans and plants. It is not virulent in healthy viable tissues. It gains access to seeds through wounds and insect larval exit holes. A. Flavus targets seeds with poor viability. In humans A. Flavus is associated with aspergillosis, a secondary respiratory infection in immuno-compromised patients. In certain areas it is also the cause of superficial infections. ² Infections A. Flavus can cause are corneal, otomycotic, and nasoorbital infections.³ A. Flavus is also an allergen. It causes allergic bronchopulmonary aspergillosis. ⁵

Ecology

Aspergillus Flavus can be found all over the world; however it is found to be abundant in places of warm temperature. Field contamination is mostly present in areas with high temperatures and drought. It is also abundant in areas with temperate climates during warm drought years. In the US it affects the corn crop in the south eastern area. ⁵

A. Flavus grows in temperatures of 25-42 C. But the best temperature for growth is 37 C. A. Flavus survives through winter as mycelium or sclerotia. Sclerotia is a resistant structure that is developed into hyphae or conidia. The conidia are then scattered into air and soil by insects or wind. ¹

Cell structure and metabolism

A. flavus is also known as a mold. Like other molds it also grows by producing hyphae. The network of hyphae, or mycelium,are responsible for secreting enzymes. The enzymes secreted are used to break down complex food sources. The complex food sources are broken down into small molecules which are then absorbed by the myceilium to grow. Mycelium contain conidia or asexual spores, these can be seen with the naked eye while the hyphae cannot be seen. Young conidia in A. flavus are yellow green and as the spores age they turn a darker green. A. Flavus can use many nutrient sources but being a saphrophyte it uses primarily dead or decaying materials.¹

Genome structure

The genome of A. Flavus strain NRRL 3357 has been sequenced at The Institute for Genomic Research, Rockville, Maryland. Below are the genome statistics.

"5 X draft

2761 scaffolds

Scaffold size, 4.5 Mbp to 200bp

91% in 16 largest scaffolds

Total size just under 40Mbp

Predicted genes, 13,487

Average gene length, 1,485 bp" ¹

References

1. http://www.aspergillusflavus.org/aflavus/

2. Mellon J, Cotty P, Dowd M. Aspergillus flavus hydrolases: their roles in pathogenesis and substrate utilization. Applied Microbiology & Biotechnology [serial online]. December 2007;77(3):497-504. Available from: Academic Search Premier, Ipswich, MA. Accessed April 12, 2009

3. http://en.wikipedia.org/wiki/Aspergillus_flavus Accessed April 13, 2009

4. Mold-Help.org. "Aspergillus." Accessed April 13, 2009

5. KLICH M. Aspergillus flavus: the major producer of aflatoxin. Molecular Plant Pathology [serial online]. November 2007;8(6):713-722. Available from: Academic Search Premier, Ipswich, MA. Accessed April 15, 2009