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''Aspergillus versicolor'' is a slow-growing filamentous
fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
commonly found in damp indoor environments and on food products. It has a characteristic musty odor associated with moldy homes and is a major producer of the hepatotoxic and carcinogenic
mycotoxin A mycotoxin (from the Greek μύκης , "fungus" and τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' ...
sterigmatocystin Sterigmatocystin is a polyketide mycotoxin produced by certain species of ''Aspergillus''. The toxin is naturally found in some cheeses. Sterigmatocystin is a toxic metabolite structurally closely related to the aflatoxins as it is the penultimate ...
. Like other ''
Aspergillus ' () is a genus consisting of several hundred mold species found in various climates worldwide. ''Aspergillus'' was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Mic ...
'' species, ''A. versicolor'' is an eye, nose, and throat irritant.


Taxonomy

The fungus was first described by Jean-Paul Vuillemin in 1903 under the name ''Sterigmatocystis versicolor'', and was later moved to the genus ''
Aspergillus ' () is a genus consisting of several hundred mold species found in various climates worldwide. ''Aspergillus'' was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Mic ...
'' by Carlo Tiraboschi in 1908. Presently, the genus ''Sterigmatocystis'' is obsolete.


Ecology

''Aspergillus versicolor'' is a highly ubiquitous species commonly isolated from soil, plant debris, marine environments, and indoor air environments. It is among the most common of indoor molds, often reported in dust and in water-damaged building materials, such as wallboards, insulation, textiles, ceiling tiles, and manufactured wood. ''Aspergillus versicolor'' is a highly resilient fungus, explaining its wide global distribution in a variety of environmental conditions. Although it grows optimally between 22 and 26 °C, ''A. versicolor'' can grow at a larger temperature range from 4–40 °C. The fungus can also tolerate a wide pH range, and is particularly resistant to alkaline conditions. The soil depth at which the fungus can be found is variable (down to 50 cm), but it appears to be particularly abundant in deeper soils. Like other members of its genus, ''A. versicolor'' displays moderate xerophillic characteristics, meaning that it can grow in conditions with low water activity (down to aW of 0.75–0.81 in the optimal temperature range). ''A. versicolor'' is also considered to be osmophilic as it is able to survive in solutions that are up to 30% NaCl or 40% sucrose. This makes the fungus an economically important spoilage organism for stored grains, rice, tea, and spices. Additionally, ''A. versicolor'' has been isolated from areas with high saline levels including the Dead Sea. Other extreme habitats from which the fungus has been reported include peat bogs, deglaciated Arctic soil, and uranium mines.


Morphology

Colonies vary greatly in colour, growth rate, and surface characteristics depending upon growth conditions. By contrast, microscopic morphology tends to be consistent independent of growth parameters. Colonies are typically white at the start of development, and change to yellow, orange, and green, often with pink or flesh hues intermixed, as they mature. Reverse pigmentation is often variable as well, especially for incubation periods greater than two weeks in duration. ''Aspergillus versicolor'' has long, septate
hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...
that appear glassy and transparent. Conidiphores, which are specialized hyphal stalks for asexual reproduction, typically measure 120–700 μm in length. Conidiophores terminate in small vesicles (10–15 μm in diameter) that are biseriate (i.e., with two successive layers of cells interposing the vesicle and conidia). The first layer of cells are called metulae upon which
phialide The phialide ( ; el, phialis, diminutive of phiale, a broad, flat vessel) is a flask-shaped projection from the vesicle (dilated part of the top of conidiophore) of certain fungi. It projects from the mycelium without increasing in length unless ...
s are borne. The vesicles are variable in shape but are often described as "spoon-shaped".
Conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to t ...
are spherical, approximately 2.5–3.5 μm in diameter, and may have smooth or slightly roughened surfaces.


Secondary metabolism

''Aspergillus versicolor'' is able to grow on a variety of surfaces, including those that are nutrient-deficient, because it is
autotrophic An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...
for most growth substances and the macronutrient
riboflavin Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved i ...
. Additionally, ''A. versicolor'' has high activity levels of
xylanase Endo-1,4-β-xylanase (EC 3.2.1.8, systematic name 4-β-D-xylan xylanohydrolase) is any of a class of enzymes that degrade the linear polysaccharide xylan into xylose, thus breaking down hemicellulose, one of the major components of plant cel ...
, an enzyme that breaks down
hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all terrestrial plant cell walls.Scheller HV, Ulvskov Hemicelluloses.// Annu Rev ...
in plant cell walls. Xylanase is a secondary metabolite controlled through gene-specific induction and
carbon catabolite repression Carbon catabolite repression, or simply catabolite repression, is an important part of global control system of various bacteria and other microorganisms. Catabolite repression allows microorganisms to adapt quickly to a preferred (rapidly metabol ...
. Many metabolites produced by ''A. versicolor'' exhibit antibacterial, fungicidal, insecticidal, and cytotoxic properties. For example, a
sesquiterpenoid Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many unique combinations. Biochemical modificatio ...
nitrobenzoyl ester isolated from hyphae have been shown to be potent inhibitor of human breast and colon cancer cell lines. Other extracted compounds that are cytotoxic towards cancer cells include xanthones,
fellutamide Fellutamides are tripeptide derivatives from '' Penicillium fellutanum'' and other fungi. They are potent proteasome inhibitor that stimulates nerve growth factor synthesis ''in vitro''. Fellutamides A and F were first isolated from ''Aspergillu ...
s, and
anthraquinones ''For the parent molecule 9,10-anthraquinone, see anthraquinone'' Anthraquinones (also known as anthraquinonoids) are a class of naturally occurring phenolic compounds based on the 9,10-anthraquinone skeleton. They are widely used industrially and ...
. Anthraquinone appears yellowish in appearance, and like other pigment molecules, it is regularly produced by ''A. versicolor''. Additional studies on the fungus have demonstrated various metabolites with activity against bacteria such as ''M. tuberculosis'' and yeasts like ''C. albicans''.
Aspergillomarasmine A Aspergillomarasmine A is an polyamino acid naturally produced by the mold ''Aspergillus versicolor''. The substance has been reported to inhibit two antibiotic resistance carbapenemase proteins in bacteria, New Delhi metallo-beta-lactamase 1 (NDM-1 ...
has been reported to inhibit two
antibiotic resistance Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
carbapenemase Beta-lactamases, (β-lactamases) are enzymes () produced by bacteria that provide multi-resistance to beta-lactam antibiotics such as penicillins, cephalosporins, cephamycins, monobactams and carbapenems ( ertapenem), although carbapenems ...
proteins in bacteria. Mycotoxins, such as nidulotoxins and
aflatoxin B1 Aflatoxin B1 is an aflatoxin produced by ''Aspergillus flavus'' and '' A. parasiticus''. It is a very potent carcinogen with a TD50 3.2 μg/kg/day in rats. This carcinogenic potency varies across species with some, such as rats and monkeys, seem ...
, are typically produced in relatively low concentrations by ''A. versicolor''. The only exception is
sterigmatocystin Sterigmatocystin is a polyketide mycotoxin produced by certain species of ''Aspergillus''. The toxin is naturally found in some cheeses. Sterigmatocystin is a toxic metabolite structurally closely related to the aflatoxins as it is the penultimate ...
, which can account for up to 1% of the total biomass of ''A. versicolor'' under optimal conditions (e.g. aW of 1). Not many spores are produced by ''A. versicolor'', so it is suspected that human exposured to sterigmatocystins occur through micro-fragments derived from the colonies.


Disease

Like other members of its species, ''A. versicolor'' is an opportunistic pathogen and is considered to be an important causative agent of
aspergillosis Aspergillosis is a fungal infection of usually the lungs, caused by the genus ''Aspergillus'', a common mould that is breathed in frequently from the air around, but does not usually affect most people. It generally occurs in people with lung dis ...
. There have been reported cases of the fungus causing onychomycosis, which is often treated with topical azoles. However, ''A. versicolor'' is insensitive to these treatments and the infection can persist even after months or years of treatment. Studies have shown that like other ''Aspergillus'' species, ''A. versicolor'' is highly sensitive to terbinafine, which has ''in vitro'' fungicidal activity. There are more than 20 allergens that have been identified from ''A. versicolor'', with the most abundant being glyceraldehyde-3-phosphate dehydrogenase. Other proteins include sorbitol reductase, catalase, enolase, malate dehydrogenase, and Asp v 13. It is common in developed countries to measure IgG responses in humans. Additionally, mycotoxins can act as immunosuppressants, which may explain some increased prevalence of frequent infections among inhabitants of damp buildings.


Industrial uses

Fungi provide an effective, economic, and environmentally-friendly method of removing harmful wastes that accumulate as byproducts of industrial activities. For example, ''A. versicolor'' is very effective at removing lead ions, adsorbing 45 mg of lead per gram of dry fungal biomass. The process proceeds quickly with 80% of ions adsorbed within an hour. ''Aspergillus versicolor'' is also useful in the industrial production and purification of xylanase, which is often used to degrade xylan in waste products from hardwood manufacturing and agricultural activities.


References

{{Taxonbar, from=Q10420082 Fungi described in 1903 versicolor