Aspergillus niger

Aspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food. It is ubiquitous in soil and is commonly reported from indoor environments, where its black colonies can be confused with those of Stachybotrys (species of which have also been called "black mold").^[1]

Some strains of A. niger have been reported to produce potent mycotoxins called ochratoxins,^[2] but other sources disagree, claiming the latter report is based upon misidentification of the fungal species. Recent evidence suggests some true A. niger strains do produce ochratoxin A.^[1][3]

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Taxonomy

A. niger is included in Aspergillus subgenus Circumdati, section Nigri. The section Nigri includes 15 related black-spored species that may be confused with A. niger, including A. tubingensis, A. foetidus, A. carbonarius, and A. awamori.^[4][5] A number of morphologically similar species were recently described by Samson et al.^[5]

Pathogenicity

Plant disease

A. niger causes black mold of onions. Infection of onion seedlings by A. niger can become systemic, manifesting only when conditions are conducive. A. niger causes a common postharvest disease of onions, in which the black conidia can be observed between the scales of the bulb. The fungus also causes disease in peanuts and in grapes. The spore comes to common trees such as maple.

Human and animal disease

A. niger is less likely to cause human disease than some other Aspergillus species, but if large amounts of spores are inhaled, a serious lung disease, aspergillosis can occur. Aspergillosis is particularly frequent among horticultural workers who inhale peat dust, which can be rich in Aspergillus spores. Less commonly, it has been found on the walls of ancient Egyptian tombs and can be inhaled when the area is disturbed. A. niger is one of the most common causes of otomycosis (fungal ear infections), which can cause pain, temporary hearing loss and, in severe cases, damage to the ear canal and tympanic membrane.  

Industrial uses

A. niger is cultured for the industrial production of many substances. Various strains of A. niger are used in the industrial preparation of citric acid (E330) and gluconic acid (E574) and have been assessed as acceptable for daily intake by the World Health Organisation.

Many useful enzymes are produced using industrial fermentation of A. niger. For example, A. niger glucoamylase is used in the production of high fructose corn syrup, and pectinases are used in cider and wine clarification. α-galactosidase, an enzyme that breaks down certain complex sugars, is a component of Beano® and other medications which the manufacturers claim can decrease flatulence. Another use for A. niger within the biotechnology industry is in the production of magnetic isotope-containing variants of biological macromolecules for NMR analysis.

Other uses

In 2006 it was reported that a secreted RNase produced by A. niger called actibind has antiangiogenic and anticarcinogenic characteristics.

A. niger is also cultured for the extraction of the enzymes glucose oxidase (GO) and Alpha-galactosidase (AGS). Glucose oxidase is used in the design of glucose biosensors, due to its high affinity for β-D-glucose.^[6] Alpha-galactosidase is produced by fermenting Aspergillus niger; it is used to hydrolyze alpha 1-6 bonds found in melibiose, raffinose, and stachyose. Reactions between flour and water will cause severe food discoloration, and if consumed by the human body raw, severe sickness can ensue. If used in food that is cooked to be consumed, it may cause vomiting and mild fevers. If you are allergic to mold, and you consume black mold in any way shape or form, seek immediate medical consulting immediately.

Genetics

The genomes of two different A. niger strains have been fully sequenced.^[7]

References