Aspergillus niger is a member of the genus Aspergillus which includes a set of fungi that are generally considered asexual, although perfect forms (forms that reproduce sexually) have been found. Aspergilli are ubiquitous in nature. They are geographically widely distributed, and have been observed in a broad range of habitats because they can colonize a wide variety of substrates. A. niger is commonly found as a saprophyte growing on dead leaves, stored grain, compost piles, and other decaying vegetation. The spores are widespread, and are often associated with organic materials and soil.
The primary uses of A. niger are for the production of enzymes and organic acids by fermentation. A. niger is also used to produce organic acids such as citric acid and gluconic acid.
Aspergillus niger can be classified as a member of the “deuteromycetes,” a “class” reserved for organisms with no known sexual state. Although they are considered a deuteromycete, modern taxonomy puts them in the phlyum of Ascomycota. Further taxonomy takes A. niger to the class of Eurotiomycetes, order of Eurotiales, family of Trichocomaceae, and genus Aspergillus.
A. niger is a ubiquitous fungus that grows very quickly. Strains can be isolated from many different ecological habitats such as soil, plant debris, rotting fruit, and even indoor air environments.
Macroscopically, this fungus can be identified growing on substrates producing colonies of felt like yellow to white hyphae, turning black with the formation of conidia.
Microscopically, A. niger can be identified by its hyaline, septate hyphae. Asexual conidiophores can be identified by being long and globose at the tip, with what appears to be a hymenial layer of structures, each “ejecting” its own spore.
While morphology provides a reasonable means of classification and assignment within the A. niger group, it is not a reliable means for identifying a given isolate from the field. The major distinction currently separating A. niger from the other species of Aspergillus is the production of carbon black or very dark brown spores from biseriate phialides (Raper and Fennell, 1965). Other features include the smooth and generally colorless conidiophores and spores that are ó5 æm, globose, and have conspicuous ridges or spines not arranged in rows. A. niger isolates grow slowly on Czapek agar (Raper and Fennell, 1965). These physical characters such as spore color and rate of growth on a defined media are subject to change, especially under extended pure culture or selection and mutation. Though A. niger is relatively stable to spontaneous mutation compared to other aspergilli, variation in morphology may still be a problem with some strains (Raper and Fennell, 1965). Thus this species may be misidentified with other Aspergillus spp.
Distinguishing the organism from other species of Aspergillus can be done macroscopically, by identifying the white felt like colony turning black with conidia formation. Microscopically one can confirm this identification by the presence of black, globose conidia with very dark to black spores.
Other species of Aspergillus have been confused with A. niger but the black conidia and spores confirm the species to be A. niger. Also, some people confuse some species of Penicillium with Aspergillus. This confusion can be easily settled by looking at the organisms microscopically. Penicillium has a paint brush looking conidium, while a Aspergillus looks more like a toilet brush, with its globose base at the end of the stalk. Stachybotrys also is confused with Aspergillus as they both grow as black colonies, but further identification at the microscopic level shows the conidial structure to be different than A. niger
Molecular Biology and Genetics
Barcode data: Aspergillus niger
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Aspergillus niger
Public Records: 4
Specimens with Barcodes: 4
Species With Barcodes: 1
Relevance to Humans and Ecosystems
A. niger is one of the most valuable fungi to humans. A. niger makes citric acid, the main ingredient in soda. Most people think citric acid is gathered from grinding citrus fruits, but that would be very expensive. Most citric acid is collected from fermenters of A. niger growing and secreting citric acid. The citric acid production by A. niger for soda is a multi million dollar operation!
Aspergillus niger is worldwide in distribution and has been isolated from numerous habitats. Humans are continually exposed to A. niger spores and vegetative forms on foodstuffs and in the air. The vast majority of strains of A. niger, especially those used in industrial fermentation, have a history of safe use. While there are sporadic reports to the contrary, most isolates have not been documented to be serious pathogens of humans, animals or plants. Specific strains may produce certain mycotoxins or may elicit allergic responses among workers. Those limited instances of adverse effects seem to be associated with a limited number of strains. With proper characterization of industrial strains, use of those with potential for such effects can be avoided.
It causes a disease called black mould on certain fruits and vegetables such as grapes, apricots, 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 mould").
Some strains of A. niger have been reported to produce potent mycotoxins called ochratoxins; other sources disagree, claiming this report is based upon misidentification of the fungal species. Recent evidence suggests some true A. niger strains do produce ochratoxin A. It also produces the isoflavone orobol.
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. A number of morphologically similar species were recently described by Samson et al.
Recently the strain of ATCC 16404 Aspergillus niger has been reclassified at Aspergillus brasiliensis (refer to publication by Varga et al.). This has required an update to the U.S. Pharmacopoeia and the European Pharmacopoeia which commonly use this strain throughout the pharmaceutical industry.
A. niger causes black mold of onions and ornamental plants. 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.
Human and animal disease
A. niger is less likely to cause human disease than some other Aspergillus species. In extremely rare instances, humans may become ill, but this is due to a serious lung disease, aspergillosis, that can occur. Aspergillosis is, in particular, frequent among horticultural workers that inhale peat dust, which can be rich in Aspergillus spores. It has been found in the mummies of ancient Egyptian tombs and can be inhaled when they are disturbed.
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. A. niger fermentation is "generally recognized as safe" (GRAS) by the United States Food and Drug Administration under the Federal Food, Drug, and Cosmetic Act.
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. Alpha-galactosidase, an enzyme that breaks down certain complex sugars, is a component of Beano and other products that 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. The enzyme Protease is derived from Aspergillus niger and used to produce the additive Clarity-Ferm. This product is being used in the brewing industry to reduce gluten content of wheat and barley based beers. A Clarity-Ferm treated beer made from barley or wheat usually tests below 20 ppm of gluten, the current international standard for gluten free.
Aspergillus niger growing from gold mining solution contained cyano metal complexes; such as gold, silver, copper iron and zinc. The fungus also plays a role in the solubilization of heavy metal sulfides. Alkali treated Aspergillus niger binds to silver to 10% of dry weight. Silver biosorbtion occurs via stoichiometric exchange with Ca(II) and Mg(II) of the sorbent.
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. Alpha-galactosidase can be produced by A. niger fermentation; it is used to hydrolyze alpha 1-6 bonds found in melibiose, raffinose, and stachyose.
Research published in 2006–2008 investigated A. niger prolyl endoprotease (AN-PEP), a microbial-derived prolyl endoprotease which cleaves gluten. This has strong implications in the treatment of coeliac disease or other metabolic gluten sensitivity disease processes. A placebo controlled, double blind study was initiated in December 2008 to determine the efficacy of this enzyme in treating humans with coeliac disease.
A. niger is often used as a challenge organism for cleaning validation studies performed within sterile manufacturing facilities.
|NCBI genome ID|
|Genome size||34 Mb|
|Number of chromosomes||8|
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