Aspergillus ochraceus

Aspergillus ochraceus is a mold species in the genus Aspergillus known to produce the toxin ochratoxin A, one of the most abundant food-contaminating mycotoxins, and citrinin. It also produces the dihydroisocoumarin mellein. It is a filamentous fungus in nature and has characteristic biseriate conidiophores. Traditionally a soil fungus, has now began to adapt to varied ecological niches, like agricultural commodities, farmed animal and marine species. In humans and animals the consumption of this fungus produces chronic neurotoxic, immunosuppressive, genotoxic, carcinogenic and teratogenic effects. Its airborne spores are one of the potential causes of asthma in children and lung diseases in humans. The pig and chicken populations in the farms are the most affected by this fungus and its mycotoxins. Certain fungicides like mancozeb, copper oxychloride, and sulfur have inhibitory effects on the growth of this fungus and its mycotoxin producing capacities. The genus Aspergillus was first described in 1729 by Pier Antonio Micheli. Under this genus the species Aspergillus ochraceus was discovered by the German botanist and mycologist Karl Adolf Wilhelm in 1877. After this discovery, some other species that looked similar to Aspergillus ochraceus were considered synonyms of this fungus. For example, Aspergillus alutaceus isolated by Berkeley in 1875, Sterigmatocystis helva isolated by Bainier in 1881, Aspergillus ochraceus var. microspora isolated by Traboschi in 1908, and Aspergillus Ochraceus- petali- formis isolated by Balista et Maia in 1957 are all considered synonyms of Aspergillus ochraceus. In 1979 two new species under the Aspergillus ochraceus group were discovered.Aspergillus bridgeri was isolated from soils collected in southcentral Wyoming and Aspergillus campestris from northcentral North Dakota. The colonies of Aspergillus ochraceus grow rapidly (45 to 55 mm in 7 days). The optimum temperature for their growth is 25 °C. In an agar plate the vegetative mycelium is mostly submerged in the agar, while the conidial heads are typically arranged in zones. The characteristic colour of the colony is yellow. Some colonies of Aspergillus ochraceus form pinkish to purple, irregular, pebble-like sclerotia up to 1 mm in diameter. The reverse look on a petri dish is pale to brownish. To the naked eye, the conidiophores of Aspergillus ochraceus appear as a powdery mass. Microscopically, smooth or finely roughened phialides are arranged on the conidial heads in a biseriate fashion (i.e., phialides are attached to intermediate cells called metulae, which in turn are attached to the vesicle). The metulae all around the perimeter grows in a radial orientation. In culture the conidial heads at first appear globose, but with age, the conidial chains adhere and develop into two or three divergent columns. Vinaceous purple sclerotia may be present. The characteristic colour of the conidiophores is chalky yellow to pale yellow-brown. The heights of the conidiophores are up to 1500 µm high. The appearances of these conidiophores are granular with pale yellow-brown walls that attach abruptly to a 'globose to subglobose vesicle'. The vesicles, which are globose with thin walls and a diameter of 35 × 50 µm, produce sterigmata over the entire surface in culture. The primary sterigmata measures 15-25 × 5-6 µm, while the secondaries are 7-11 × 2-3.3 µm. The conidia are arranged in dry, upright chains, often massing into two or more short columns per head, in wet microscopic mounts hyaline. The diameter of the conidia are around 2.5-3.5 µm. Aspergillus ochraceus produces a mycotoxin named ochratoxin A (OTA). Mellein and 4-hydroxymellein are other toxic metabolites produced by this fungus. The ecological roots of Aspergillus ochraceus lay in the soil. This fungus was first isolated from varied soils. Evolutionary development has now well adapted Aspergillus ochraceus to occupy a great variety of environmental niches. It has been isolated from the marine alga Sargassum miyabei. This fungus has also been found in a wide variety of agricultural commodities like corn, peanuts, cottonseed, rice, tree nuts, cereal grains, and fruits. Similarly the presence of this fungus has been documented in coffee beans Apart from the actual colonies of fungi growing on substances, the toxins and metabolites produced by this fungus have also been found in a variety of places. For example, the mycotoxin OTA produced by this fungus was found to be present in airborne dust. Likewise, secondary metabolites of this fungus have been isolated from marine sponges. This fungus has also been found to be associated with the contamination of an edible caterpillar, named the phane worm. In terms of climate preferences, this fungus has been found to mainly colonise temperate and tropical geographical areas. Ochratoxin A (OTA), a mycotoxin produced by A. ochraceus, contaminates food and initiates apoptosis of plant cells. Significant loss in nutritive value and hazardous effect on the food chain are caused due to the same OTA toxin contamination in barley grains of Spain. OTA has been isolated from plant acquired foods products like cereal, vegetables, coffee, wine, liquorice and also animal acquired food products like pork and poultry. Apart from being found in human food products from farm animals, this fungus was also isolated from the poultry feed. Aspergillus ochraceus produces both OTA and Penicillic acid in poultry feed at optimum temperatures and moisture levels. Combinations of low temperature and moisture favored the growth of Penicillic acid, on the other hand combinations of high temperature and moisture favored the growth of OTA. In addition to poulty and agricultural products the harvesting of edible insects is also an important economic activity. The rural population of Botswana eat a caterpillar called 'phane worm'. As already mentioned above, this lepidopteran larva is often contaminated by A. ochraceus. So this fungus is also of economic importance in cultures that consume insects. Wineries are also subject to losses resulting from OTA contamination as a result of A. ochraceus grows on grapes, dried vine fruits and wine. Aspergillus ochraceus was used for the industrial production of xylanase and β-xylosidase. In addition to producing enzymes, recently in a study done by Lee Ki in 2013, Aspergillus ochraceus was found to inhibit the growth of a Shiga toxin-producing bacteria called Escherichia coli (STEC) O157, implicating industrial use of this phenomenon to develop anti-bacterial drugs. In another study pertaining to the conversion of Xanthohumol, a prenylated chalconoid, which has antioxidant and anticancer properties, Aspergillus ochraceus was found to be able to convert it into a stronger antioxidant, increasing the compounds radical scavenging properties. The process of fermentation was found to be enhanced by the addition of Aspergillus ochraceus in the substrate mixture, which contained wheat bran and wheat straw liquor. The secondary metabolites of this fungus have shown to possess antibacterial activities that manifest the potential to inhibit human pathogens. For example, α- Campholene aldehyde, Lucenin-2 and 6-Ethyloct- 3-yl- 2- ethylhexyl ester are the three secondary metabolites that showed antimicrobial effects against potential human pathogens.