Aspergillus terreus

Aspergillus terreus, also known as Aspergillus terrestris, is a fungus (mold) found worldwide in soil. Although thought to be strictly asexual until recently, A. terreus is now known to be capable of sexual reproduction. This saprotrophic fungus is prevalent in warmer climates such as tropical and subtropical regions. Aside from being located in soil, A. terreus has also been found in habitats such as decomposing vegetation and dust. A. terreus is commonly used in industry to produce important organic acids, such as itaconic acid and cis-aconitic acid, as well as enzymes, like xylanase. It was also the initial source for the drug mevinolin (lovastatin), a drug for lowering serum cholesterol. Aspergillus terreus can cause opportunistic infection in people with deficient immune systems. It is relatively resistant to amphotericin B, a common antifungal drug. Aspergillus terreus also produces aspterric acid and 6-hydroxymellein, inhibitors of pollen development in Arabidopsis thaliana. Aspergillus terreus is brownish in colour and gets darker as it ages on culture media. On Czapek or malt extract agar (MEA) medium at 25 °C (77 °F), colonies have the conditions to grow rapidly and have smooth-like walls. In some cases, they are able to become floccose, achieving hair-like soft tufts. Colonies on malt extract agar grow faster and sporulate more densely than on many other media. Aspergillus terreus has conidial heads that are compact, biseriate, and densely columnar, reaching 500 × 30–50 µm in diameter. Conidiophores of A. terreus are smooth and hyaline up to 100–250 × 4–6 µm in diameter. The conidia of A. terreus are small, about 2 µm in diameter, globose-shaped, smooth-walled, and can vary from light yellow to hyaline. Unique to this species is the production of aleurioconidia, asexual spores produced directly on the hyphae that are larger than the phialoconidia (e.g. 6–7 µm in diameter). This structure might be influential in the way A. terreus presents itself clinically as it can induce elevated inflammatory responses. This fungus is readily distinguished from the other species of Aspergillus by its cinnamon-brown colony colouration and its production of aleurioconidia. A. terreus is a thermotolerant species since it has optimal growth in temperatures between 35–40 °C (95–104 °F), and maximum growth within 45–48 °C (113–118 °F). Aspergillus terreus, like other species of Aspergillus, produces spores that disperse efficiently in the air over a range of distances. The morphology of this fungus provides an accessible way for spores to disperse globally in air current. Elevation of the sporulating head atop a long stalk above the growing surface may facilitate spore dispersal through the air. Normally, spores in fungi are discharged into still air, but in A. terreus, it resolves this problem with a long stalk and it allows the spores to discharge into air currents like wind. In turn, A. terreus has a better chance to disperse its spores amongst a vast geography which subsequently explains for the worldwide prevalence of the fungus. Despite A. terreus being found worldwide in warm, arable soil, it has been located in many different habitats such as compost and dust. Eventually, the dispersed fungal spores come into contact with either liquid or solid material and settle onto it, but only when the conditions are right do the spores germinate. One of the conditions important to the fungus is the level of moisture present in the material. The lowest water activity (Aw) capable of supporting growth of the fungus has been reported as 0.78. Tolerance of relatively low Aw conditions may explain, in part, the ubiquitous nature of this species given its ability to grow is a wide array of places. The soil of potted plants is one common habitat supporting the growth of A. terreus, and colonized soils may be important reservoirs of nosocomial infection. Other habitats include cotton, grains, and decomposing vegetation. The Broad Fungal Genome Initiative funded by the National Institute of Allergy and Infectious Disease carried out the sequencing A. terreus in 2006. The result was 11.05 × genome sequence coverage. A. terreus contains 30-35 Mbp and roughly 10,000 protein-coding genes. Identification of virulence determinants within the genome of A. terreus may facilitate the development of new approaches to the treatment of A. terreus-related diseases. In addition, because A. terreus is resistant to the common antifungal drug amphotericin B, the mechanisms underlying its resistance may be better understood by genome-level investigation.