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''Aspergillus'' () is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
consisting of several hundred
mold A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...
species found in various climates worldwide. ''Aspergillus'' was first catalogued in 1729 by the Italian priest and biologist
Pier Antonio Micheli Pier Antonio Micheli (December 11, 1679 – January 1, 1737) was a noted Italian botanist, professor of botany in Pisa, curator of the Orto Botanico di Firenze, author of ''Nova plantarum genera iuxta Tournefortii methodum disposita''. He discove ...
. Viewing the fungi under a microscope, Micheli was reminded of the shape of an ''
aspergillum An aspergillum (less commonly, aspergilium or aspergil) is a Christian liturgical implement used to sprinkle holy water. It comes in three forms: a freshly cut hyssop branch, a brush-like bundle that is dipped in the holy water and shaken, an ...
'' (holy water sprinkler), from Latin ''spargere'' (to sprinkle), and named the genus accordingly. Aspergillum is an asexual spore-forming structure common to all ''Aspergillus'' species; around one-third of species are also known to have a sexual stage. While some species of ''Aspergillus'' are known to cause fungal infections, others are of commercial importance.


Taxonomy


Species

''Aspergillus'' consists of 837 species of fungi.


Growth and distribution

''Aspergillus'' is defined as a group of conidial fungi—that is, fungi in an asexual state. Some of them, however, are known to have a
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 asex ...
(sexual state) in the Ascomycota. With DNA evidence, all members of the genus ''Aspergillus'' are members of the phylum Ascomycota. Members of the genus possess the ability to grow where a high osmotic pressure exists (high concentration of sugar, salt, etc.). ''Aspergillus'' species are highly
aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cel ...
and are found in almost all oxygen-rich environments, where they commonly grow as
mold A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...
s on the surface of a substrate, as a result of the high oxygen tension. Commonly, fungi grow on carbon-rich substrates like monosaccharides (such as
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
) and
polysaccharides Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...
(such as
amylose Amylose is a polysaccharide made of α-D-glucose units, bonded to each other through α(1→4) glycosidic bonds. It is one of the two components of starch, making up approximately 20–30%. Because of its tightly packed helical structure, amylose ...
). ''Aspergillus'' species are common contaminants of starchy foods (such as bread and potatoes), and grow in or on many plants and trees. In addition to growth on carbon sources, many species of ''Aspergillus'' demonstrate
oligotroph An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates o ...
y where they are capable of growing in nutrient-depleted environments, or environments with a complete lack of key nutrients. ''
Aspergillus niger ''Aspergillus niger'' is a mold classified within the ''Nigri'' section of the ''Aspergillus'' genus. The ''Aspergillus'' genus consists of common molds found throughout the environment within soil and water, on vegetation, in fecal matter, on de ...
'' is a prime example of this; it can be found growing on damp walls, as a major component of
mildew Mildew is a form of fungus. It is distinguished from its closely related counterpart, mould, largely by its colour: moulds appear in shades of black, blue, red, and green, whereas mildew is white. It appears as a thin, superficial growth consi ...
. Several species of ''Aspergillus'', including ''A. niger'' and '' A. fumigatus'', will readily colonise buildings, favouring warm and damp or humid areas such as
bathroom A bathroom or washroom is a room, typically in a home or other residential building, that contains either a bathtub or a shower (or both). The inclusion of a wash basin is common. In some parts of the world e.g. India, a toilet is typically ...
s and around
window frame A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent mate ...
s. ''Aspergillus'' are found in millions of pillows.


Commercial importance

Species of ''Aspergillus'' are important medically and commercially. Some species can cause infection in humans and other animals. Some infections found in animals have been studied for years, while other species found in animals have been described as new and specific to the investigated disease, and others have been known as names already in use for organisms such as saprophytes. More than 60 ''Aspergillus'' species are medically relevant pathogens. For humans, a range of diseases such as infection to the external ear, skin lesions, and ulcers classed as mycetomas are found. Other species are important in commercial microbial fermentations. For example, alcoholic beverages such as Japanese ''
sake Sake, also spelled saké ( ; also referred to as Japanese rice wine), is an alcoholic beverage of Japanese origin made by fermenting rice that has been polished to remove the bran. Despite the name ''Japanese rice wine'', sake, and indee ...
'' are often made from rice or other starchy ingredients (like
manioc ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names), is a woody shrub of the spurge family, Euphorbiaceae, native to South America. Although a perennial plant, cassava is extensively cultivated ...
), rather than from grapes or malted barley. Typical microorganisms used to make alcohol, such as yeasts of the genus ''
Saccharomyces ''Saccharomyces'' is a genus of fungi that includes many species of yeasts. ''Saccharomyces'' is from Greek σάκχαρον (sugar) and μύκης (fungus) and means ''sugar fungus''. Many members of this genus are considered very important in f ...
'', cannot ferment these starches. Therefore, ''koji'' mold such as '' Aspergillus oryzae'' is used to first break down the starches into simpler sugars. Members of the genus are also sources of natural products that can be used in the development of medications to treat human disease. ''Aspergillus'' spp. are known to produce anthraquinone which has commercial importance due to its antibacterial and antifungal properties. Perhaps the largest application of ''
Aspergillus niger ''Aspergillus niger'' is a mold classified within the ''Nigri'' section of the ''Aspergillus'' genus. The ''Aspergillus'' genus consists of common molds found throughout the environment within soil and water, on vegetation, in fecal matter, on de ...
'' is as the major source of
citric acid Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in ...
; this organism accounts for over 99% of global citric acid production, or more than 1.4 million
tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000  kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s (>1.5 million US tons) per year. ''A. niger'' is also commonly used for the production of native and foreign enzymes, including
glucose oxidase The glucose oxidase enzyme (GOx or GOD) also known as notatin (EC number 1.1.3.4) is an oxidoreductase that catalyses the oxidation of glucose to hydrogen peroxide and D-glucono-δ-lactone. This enzyme is produced by certain species of fungi and ...
,
lysozyme Lysozyme (EC 3.2.1.17, muramidase, ''N''-acetylmuramide glycanhydrolase; systematic name peptidoglycan ''N''-acetylmuramoylhydrolase) is an antimicrobial enzyme produced by animals that forms part of the innate immune system. It is a glycoside ...
, and
lactase Lactase is an enzyme produced by many organisms. It is located in the brush border of the small intestine of humans and other mammals. Lactase is essential to the complete digestion of whole milk; it breaks down lactose, a sugar which gives ...
. In these instances, the culture is rarely grown on a solid substrate, although this is still common practice in Japan, but is more often grown as a submerged culture in a
bioreactor A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances ...
. In this way, the most important parameters can be strictly controlled, and maximal productivity can be achieved. This process also makes it far easier to separate the chemical or enzyme of importance from the medium, and is therefore far more cost-effective.


Research

'' A. nidulans'' (''Emericella nidulans'') has been used as a research organism for many years and was used by
Guido Pontecorvo Guido Pellegrino Arrigo Pontecorvo FRS FRSE (29 November 1907 – 25 September 1999) was an Italian-born Scottish geneticist. Life Guido Pontecorvo was born on 29 November 1907 in Pisa into a family of wealthy Italian industrialists. He was on ...
to demonstrate
parasexuality The parasexual cycle, a process restricted to fungi and single-celled organisms, is a nonsexual mechanism of parasexuality for transferring genetic material without meiosis or the development of sexual structures. It was first described by Italian ...
in fungi. Recently, ''A. nidulans'' was one of the pioneering organisms to have its
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
sequenced by researchers at the
Broad Institute The Eli and Edythe L. Broad Institute of MIT and Harvard (IPA: , pronunciation respelling: ), often referred to as the Broad Institute, is a biomedical and genomic research center located in Cambridge, Massachusetts, United States. The institu ...
. As of 2008, a further seven ''Aspergillus'' species have had their genomes sequenced: the industrially useful ''A. niger'' (two strains), '' A. oryzae'', and '' A. terreus'', and the pathogens '' A. clavatus'', '' A. fischerianus'' (''Neosartorya fischeri''), '' A. flavus'', and '' A. fumigatus'' (two strains). ''A. fischerianus'' is hardly ever pathogenic, but is very closely related to the common pathogen ''A. fumigatus''; it was sequenced in part to better understand ''A. fumigatus'' pathogenicity.


Sexual reproduction

Of the 250 species of aspergilli, about 64% have no known sexual state. However, many of these species likely have an as yet unidentified sexual stage.
Sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...
occurs in two fundamentally different ways in fungi. These are outcrossing (in
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 ...
fungi) in which two different individuals contribute nuclei, and self-fertilization or selfing (in
homothallic Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually; i.e., having male and female reproductive structures on the same thallus. The opposite sexual functions are performed by different cells of a si ...
fungi) in which both nuclei are derived from the same individual. In recent years, sexual cycles have been discovered in numerous species previously thought to be asexual. These discoveries reflect recent experimental focus on species of particular relevance to humans. ''A. fumigatus'' is the most common species to cause disease in
immunodeficient Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...
humans. In 2009, ''A. fumigatus'' was shown to have a heterothallic, fully functional sexual cycle. Isolates of complementary
mating type Mating types are the microorganism equivalent to sexes in multicellular lifeforms and are thought to be the ancestor to distinct sexes. They also occur in macro-organisms such as fungi. Definition Mating types are the microorganism equivalent to ...
s are required for
sex Sex is the trait that determines whether a sexually reproducing animal or plant produces male or female gametes. Male plants and animals produce smaller mobile gametes (spermatozoa, sperm, pollen), while females produce larger ones ( ova, of ...
to occur. ''A. flavus'' is the major producer of
carcinogenic 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 subs ...
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, sweetcorn ...
s in crops worldwide. It is also an opportunistic human and animal
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
, causing aspergillosis in immunocompromised individuals. In 2009, a sexual state of this
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 ...
fungus was found to arise when strains of opposite
mating type Mating types are the microorganism equivalent to sexes in multicellular lifeforms and are thought to be the ancestor to distinct sexes. They also occur in macro-organisms such as fungi. Definition Mating types are the microorganism equivalent to ...
s were cultured together under appropriate conditions. '' A. lentulus'' is an opportunistic human pathogen that causes invasive aspergillosis with high
mortality rate Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of d ...
s. In 2013, ''A. lentulus'' was found to have a heterothallic functional sexual breeding system. ''A. terreus'' is commonly used in industry to produce important organic acids and enzymes, and was the initial source for the cholesterol-lowering drug
lovastatin Lovastatin, sold under the brand name Mevacor among others, is a statin medication, to treat high blood cholesterol and reduce the risk of cardiovascular disease. Its use is recommended together with lifestyle changes. It is taken by mouth. ...
. In 2013, ''A. terreus'' was found to be capable of sexual reproduction when strains of opposite mating types were crossed under appropriate culture conditions. These findings with ''Aspergillus'' species are consistent with accumulating evidence, from studies of other
eukaryotic Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...
species, that sex was likely present in the common ancestor of all eukaryotes. ''A. nidulans'', a homothallic fungus, is capable of self-fertilization. Selfing involves activation of the same mating pathways characteristic of sex in outcrossing species, i.e. self-fertilization does not bypass required pathways for outcrossing sex, but instead requires activation of these pathways within a single individual. Among those ''Aspergillus'' species that exhibit a sexual cycle, the overwhelming majority in nature are homothallic (self-fertilizing). This observation suggests ''Aspergillus'' species can generally maintain sex though little
genetic variability Genetic variability is either the presence of, or the generation of, genetic differences. It is defined as "the formation of individuals differing in genotype, or the presence of genotypically different individuals, in contrast to environmentally i ...
is produced by homothallic self-fertilization. ''A. fumigatus'', a heterothallic (outcrossing) fungus that occurs in areas with widely different climates and environments, also displays little genetic variability either within geographic regions or on a global scale, again suggesting sex, in this case outcrossing sex, can be maintained even when little genetic variability is produced.


Genomics

The simultaneous publication of three ''Aspergillus'' genome manuscripts in ''
Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...
'' in December 2005 established the genus as the leading filamentous fungal genus for comparative genomic studies. Like most major genome projects, these efforts were collaborations between a large sequencing centre and the respective community of scientists. For example, the Institute for Genome Research (TIGR) worked with the ''A. fumigatus'' community. ''A. nidulans'' was sequenced at the Broad Institute. ''A. oryzae'' was sequenced in Japan at the
National Institute of Advanced Industrial Science and Technology The , or AIST, is a Japanese research facility headquartered in Tokyo, and most of the workforce is located in Tsukuba Science City, Ibaraki, and in several cities throughout Japan. The institute is managed to integrate scientific and engineeri ...
. The Joint Genome Institute of the Department of Energy has released sequence data for a citric acid-producing strain of ''A. niger''. TIGR, now renamed the J. Craig Venter Institute, is currently spearheading a project on the ''A. flavus'' genome. ''Aspergillus'' is characterized by high levels of genetic diversity and, using protostome divergence as a scale, is as diverse as the Vertebrates phylum although both inter and intra-specific genome structure is relatively plastic. The genomes of some ''Aspergillus'' species, such as ''A. flavus'' and ''A. oryzae'', are more rich and around 20% larger than others, such as ''A. nidulans'' and ''A. fumigatus''. Several mechanisms could explain this difference, although the combination of segmental duplication, genome duplication, and horizontal gene transfer acting in a piecemeal fashion is well-supported. Genome sizes for sequenced species of ''Aspergillus'' range from about 29.3 Mb for ''A. fumigatus'' to 37.1 Mb for ''A. oryzae'', while the numbers of predicted genes vary from about 9926 for ''A. fumigatus'' to about 12,071 for ''A. oryzae''. The genome size of an enzyme-producing strain of ''A. niger'' is of intermediate size at 33.9 Mb.


Pathogens

Some ''Aspergillus'' species cause serious disease in humans and animals. The most common pathogenic species are '' A. fumigatus'' and '' A. flavus'', which produces
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, sweetcorn ...
which is both a toxin and a carcinogen, and which can contaminate foods such as nuts. The most common species causing
allergic Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic der ...
disease are ''A. fumigatus'' and '' A. clavatus''. Other species are important as agricultural pathogens. ''Aspergillus'' spp. cause disease on many grain crops, especially
maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
, and some variants synthesize
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' ...
s, including aflatoxin. ''Aspergillus'' can cause
neonatal infection Neonatal infections are infections of the neonate (newborn) acquired during prenatal development or in the first four weeks of life (neonatal period). Neonatal infections may be contracted by mother to child transmission, in the birth canal dur ...
s. ''A. fumigatus'' (the most common species) infections are primary pulmonary infections and can potentially become a rapidly necrotizing pneumonia with a potential to disseminate. The organism can be differentiated from other common mold infections based on the fact that it takes on a mold form both in the environment and in the host (unlike ''
Candida albicans ''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usu ...
'' which is a dimorphic mold in the environment and a yeast in the body).


Aspergillosis

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 di ...
is the group of diseases caused by ''Aspergillus''. The most common species among paranasal sinus infections associated with aspergillosis is '' A. fumigatus''. The symptoms include fever, cough, chest pain, or breathlessness, which also occur in many other illnesses, so diagnosis can be difficult. Usually, only patients with already weakened
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...
s or who suffer other lung conditions are susceptible. In humans, the major forms of disease are: * Acute invasive aspergillosis, a form that grows into surrounding tissue, more common in those with weakened
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...
s such as AIDS or
chemotherapy Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemothe ...
patients * Allergic bronchopulmonary aspergillosis, which affects patients with respiratory diseases such as
asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
, cystic fibrosis, and
sinusitis Sinusitis, also known as rhinosinusitis, is inflammation of the mucous membranes that line the sinuses resulting in symptoms that may include thick nasal mucus, a plugged nose, and facial pain. Other signs and symptoms may include fever, head ...
*
Aspergilloma An aspergilloma is a clump of mold which exists in a body cavity such as a paranasal sinus or an organ such as the lung. By definition, it is caused by fungi of the genus ''Aspergillus''. Signs and symptoms People with aspergillomata typically rem ...
, a "fungus ball" that can form within cavities such as the lung * Disseminated invasive aspergillosis, an infection spread widely through the body
Fungal 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 from th ...
infections from Aspergillus spores remain one theory of sickness and untimely death of some early Egyptologists and tomb explorers. Ancient spores which grew on the remains of food offerings and mummies sealed in tombs and chambers may have been blown around and inhaled by the excavators, ultimately linked to the notion of the
curse of the pharaohs The curse of the pharaohs or the mummy's curse is a curse alleged to be cast upon anyone who disturbs the mummy of an ancient Egyptian, especially a pharaoh. This curse, which does not differentiate between thieves and archaeologists, is claime ...
. Aspergillosis of the air passages is also frequently reported in birds, and certain species of ''Aspergillus'' have been known to infect insects. Most people inhale ''Aspergillus'' into their lungs everyday. But it's generally only the immuno-compromised who get sick with
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 di ...
.


See also

* List of'' Aspergillus'' species * Mold health issues * Sick building syndrome


References


Further reading

* * * *


External links


Aspergillus Comparative Database
Comparative genomic resource at the
Broad Institute The Eli and Edythe L. Broad Institute of MIT and Harvard (IPA: , pronunciation respelling: ), often referred to as the Broad Institute, is a biomedical and genomic research center located in Cambridge, Massachusetts, United States. The institu ...

Aspergillus Genome Resources (NIH)

''Aspergillus'' surveillance project at a large tertiary-care hospital.
( PDF).
Central Aspergillus Data Repository

FungiDB: An integrated functional genomics database for fungi and oomycetes

Mold and Mildew

The Aspergillus Genome Database

The Aspergillus/Aspergillosis Website
An encyclopedia of ''Aspergillus'' for patients, doctors and scientists
The Fungal Genetics Stock Center
{{Authority control Parasitic fungi Eurotiomycetes genera