''Aspergillus parasiticus'' is a fungus belonging 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, Mich ...

''. This species is an unspecialized

saprophytic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ( ...

mold, mostly found outdoors in areas of rich soil with decaying plant material as well as in dry grain storage facilities. Often confused with the closely related species, ''A. flavus'', ''A. parasiticus'' has defined morphological and molecular differences. ''Aspergillus parasiticus'' is one of three fungi able to produce the mycotoxin,

aflatoxin Aflatoxins are various poisonous carcinogens and mutagens that are produced by certain molds, particularly ''Aspergillus'' species. The fungi grow in soil, decaying vegetation and various staple foodstuffs and commodities such as hay, sweetco ...

, one of the most

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substa ...

ic naturally occurring substances. Environmental stress can upregulate aflatoxin production by the fungus, which can occur when the fungus is growing on plants that become damaged due to exposure to poor weather conditions, during drought, by insects, or by birds. In humans, exposure to ''A. parasiticus'' toxins can cause delayed development in children and produce serious liver diseases and/or hepatic carcinoma in adults. The fungus can also cause the infection known as aspergillosis in humans and other animals. ''A. parasiticus'' is of agricultural importance due to its ability to cause disease in corn, peanut, and cottonseed.

History and taxonomy

''Aspergillus parasiticus'' was first discovered in 1912 by pathopathologist, A.T Speare from dead mealy bugs collected on Hawaiian sugarcane plantations. The species epithet, "parasiticus" is derived from the Latin word meaning "parasite" and was selected due to the ability of the fungus to parasitize other organisms. The fungus was originally classified as a subspecies of ''A. flavus'' called ''Aspergillus flavus subsp. parasiticus'' (Speare) due to its strong resemblance to ''A. flavus''. Indeed, this fungus is very closely related to ''A. flavus'' and is often misidentified as the latter. However, the two species are separable based on morphological features. ''A. parasiticus'' also exhibits physiological differences from ''A. flavus'' such as the inability to produce

cyclopiazonic acid Cyclopiazonic acid (α-CPA), a mycotoxin and a fungal neurotoxin, is made by the molds ''Aspergillus'' and ''Penicillium''. It is an indole-tetramic acid that serves as a toxin due to its ability to inhibit calcium-dependent ATPases found in the e ...

and the production of aflatoxin G.

Growth and morphology

The conidia of ''A. parasiticus'' have rough, thick walls, are spherical in shape, have short

conidiophores 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 th ...

(~400 μm) with small vesicles averaging 30 μm in size to which the phialides are directly attached. ''A. parasiticus'' is further distinguished by its dark green colony colour. ''Aspergillus parasiticus'' colonies are dark green. The average growth temperature for this fungus ranges between 12 and 42 °C with the optimum temperature for growth is at 32 °C and no growth reported at 5 °C. Growth pH ranges from 2.4 to 10.5 with the optimum growth ranging between 3.5-8. For the best growth of the fungus the carbon and nitrogen content in the soil is 1:1 and the pH 5.5. ''A. parasiticus'' normally reproduces asexually however, the presence of single mating genes MAT1-1 or MAT1-2 in different strains of the fungus suggests it has a

heterothallic Heterothallic species have sexes that reside in different individuals. The term is applied particularly to distinguish heterothallic fungi, which require two compatible partners to produce sexual spores, from homothallic ones, which are capable of ...

mating system and may have a hitherto unrecognized

teleomorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an as ...

. ''A. parasiticus'' grows on cereal agar, Czapek agar, malt extract agar, malt salt agar, and

potato dextrose agar Potato dextrose agar (BAM Media M127
from the U.S.

. The

sclerotia A sclerotium (; (), is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until favor ...

and

stromata The ''Stromata'' ( el, Στρώματα), a mistake for ''Stromateis'' (Στρωματεῖς, "Patchwork," i.e., ''Miscellanies''), attributed to Clement of Alexandria (c. 150 – c. 215), is the third of a trilogy of works regarding the Chris ...

transform from white to pink, dark brown and black. When grown on "Aspergillus flavus and parasiticus" agar (AFPA), colonies show an orange yellow reverse colouration. The conidia are pink when grown on media containing

anisaldehyde 4-Anisaldehyde, or ''p''-Anisaldehyde, is an organic compound with the formula CH3OC6H4CHO. The molecule consists of a benzene ring with an formyl and a methoxy group. It is a colorless liquid with a strong aroma. It provides sweet, floral and ...

. ''A. parasiticus'' has been cultivated on both Czapek yeast extract agar (CYA) plates and Malt Extract Agar Oxoid (MEAOX) plates. The growth morphology of the colonies can be seen in the pictures below. Aspergillus_parasiticus_cya.png, ''Aspergillus parasiticus'' growing on CYA plate Aspergillus_parasiticus_meaox.png, ''Aspergillus parasiticus'' growing on MEAOX plate

Physiology

''A. parasiticus'' produces aflatoxins B1, B2, G1, and G2, named for the colours emitted under UV light on thin-layer chromatography plates—either blue and green. The numbers refer to the type of compound with 1 being major and 2 being minor. These aflatoxins are carcinogenic mycotoxins which have detrimental effects to humans and livestock. ''A. parasiticus ''also has the ability to produce

kojic acid Kojic acid is a chelation agent produced by several species of fungi, especially ''Aspergillus oryzae'', which has the Japanese common name ''koji''. Kojic acid is a by-product in the fermentation process of malting rice, for use in the manufactur ...

, aspergillic acid, nitropropionic acid and aspertoxin as secondary antimicrobial metabolites in response to different environments, all of which can be useful in identification. ''A. parasiticus'' also differs in

quantity number, volume, and shape. This fungus can be reliably identified using molecular methods. ''A. parasiticus'' produces aflatoxins at higher concentrations than ''A. flavus'' in temperatures ranging from with pH ranging from 3 to greater than 8. Light exposure, oxidative growth conditions, fungal volatiles and nutrient availability (sugars and zinc) affect the production of these toxins. Greater zinc availability increases aflatoxin output. Environmental stress caused by drought and/or high temperatures during the latter part of the growing season of crops increases the likelihood of fungal growth. The aflatoxins produced by ''A. parasiticus'' are hazardous under normal food handling conditions and are especially stable when absorbed by starch or protein on the surfaces of seeds.

Signs and symptoms

Often, food illnesses are not attributed to ''A. parasiticus'' because it is mistaken for ''A. flavus.'' Serious symptoms of aflatoxin exposure by either ingestion or inhalation of spores, or through direct skin contact, can occur amongst humans and animals. Signs and symptoms of exposure in humans may include delayed development and stunted growth among children, while adults may experience

teratogenic Teratology is the study of abnormalities of physiological development in organisms during their life span. It is a sub-discipline in medical genetics which focuses on the classification of congenital abnormalities in dysmorphology. The related ...

effects, lung damage, ulcers, skin irritation, fever, and acute liver disease, which can later lead to liver carcinoma and death.

Control and management

Most countries put low limits on how much aflatoxin is allowed to be in food. This fungus has low resistance to heat, so in order to reduce flatoxinlevels and its toxic effects, foods such as peanuts, hazelnuts, walnuts,

pistachio The pistachio (, ''Pistacia vera''), a member of the Anacardiaceae, cashew family, is a small tree originating from Central Asia and the Middle East. The tree produces nut (fruit)#Culinary definition and uses, seeds that are widely consumed as f ...

s, and pecans can be roasted, can be treated with an alkali such as ammonia, or the crops can be given a microbial treatment. The growth of this fungus can be prevented by proper water management and dust reduction. Corn contaminated by ''A. parasiticus'' can be pasteurized by exposure to radio frequency (although any mycotoxins produced in situ will remain intact). Exposure of the fungus to phenolic compounds destabilizes the cellular lipoprotein membrane by increasing hydrophobicity, resulting in a lengthened lag phase, reduction of growth rate and diminished aflatoxin production. Similarly, exposure to phytochemicals such as

ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) and ...

, gallic acid, caffeine, and quercetin reduces the growth rate of ''A. parasiticus''.

Habitat and ecology

''Aspergillus parasiticus'' can be found outdoors commonly within an agricultural setting of soil on fields and through the improper handling, drying, transportation and storage of grains and fresh produce. This fungus is also commonly found on the stems and roots of peanuts and other plants. ''A. parasiticus'' is a tropical and subtropical species found in the United States, Latin America, South Africa, India and Australia. This species has rarely been reported from Southeast Asia and cool temperate zones. Fungal spores can be distributed with the wind as well as through moist soil via contact with nuts and kernels, and can survive over the winter months on plant material on the soil.

References

{{Taxonbar , from = Q432356 parasticus