''Cladosporium sphaerospermum'' is a

radiotrophic fungus Radiotrophic fungi are fungi that can use radiation as an energy source to stimulate growth. Radiotrophic fungi have been found in extreme environments such as in the Chernobyl Nuclear Power Plant. Most known radiotrophic fungi utilize melanin i ...

belonging to the genus ''

Cladosporium ''Cladosporium'' is a genus of fungi including some of the most common indoor and outdoor molds. Species produce olive-green to brown or black colonies, and have dark-pigmented conidia that are formed in simple or branching chains. Many species ...

'' and was described in 1886 by

Albert Julius Otto Penzig Albert Julius Otto Penzig, also referred to as Albertus Giulio Ottone Penzig (15 March 1856, Samitz, Silesia – 6 March 1929, Genoa) was a German mycologist. In 1877 he earned his degree from University of Breslau, afterwards serving as an ass ...

from the decaying leaves and branches of ''

Citrus ''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as Orange (fruit), oranges, Lemon, lemons, grapefruits, pomelos, and lim ...

''. It is a dematiaceous (darkly-pigmented)

fungus 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 ...

characterized by slow growth and largely asexual reproduction. ''Cladosporium sphaerospermum'' consists of a complex of poorly morphologically differentiated, "cryptic" species that share many physiological and

ecological Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...

attributes. In older literature, all of these sibling species were classified as ''C. sphaerospermum'' despite their unique nature. Accordingly, there is confusion in older literature reports on the physiological and habitat regularities of ''C. sphaerospermum'' in the strict sense. This fungus is most

phylogenetically In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

similar to '' C. fusiforme''. According to modern phylogenetic analyses, the previously synonymized species, ''Cladosporium langeroni'', is a distinct species.

Growth and morphology

The

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e of ''Cladosporium sphaerospermum'' are thick walled,

septate In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatr ...

, and olivaceous-brown in colour. Colonies of the fungus are velvety in texture and flattened (i.e., rarely raised, fluffy, or radially furrowed). ''C. sphaerospermum''

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 ...

are branched, septate, and dark, up to 150–300 μm long and 3.5–4.0 μm wide. The structure of the conidiophores are tree-like, a prominent feature of the genus ''Cladosporium''. Unlike other related species, the conidiophores of this species lack swollen nodes at the branching points. Conidia of this species are characteristically globose to ellipsoid with a diameter of 3.4–4.0 μm. The conidia are formed in branching chains in which the youngest conidium is situated at the top. ''Cladosporium sphaerospermum'' also produces ramoconidia 6–14 × 3.5–4.0 μm in length and this feature can be used as a method of distinguishing between similar species. Ramoconidia are conidia found at the branching points joining multiple spore chains and can be recognized by one end having a single attachment scar and the other end having two or more attachment scars. ''Cladosporium sphaerospermum'' is also a

psychrophilic Psychrophiles or cryophiles (adj. ''psychrophilic'' or ''cryophilic'') are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from to . They have an optimal growth temperature at . They are found in ...

fungus, known to grow at temperatures as low as with an upper limit of and no growth at . The optimal temperature this fungus grows under is . This fungus is xerotolerant as it can thrive in environments with low water activity caused by high salinity (

halotolerant Halotolerance is the adaptation of living organisms to conditions of high salinity. Halotolerant species tend to live in areas such as hypersaline lakes, coastal dunes, saline deserts, salt marshes, and inland salt seas and springs. Halophiles are ...

) or other dissolved solutes. This fungus has been observed to grow in as low as 0.815 a_w ''in vitro''.

Physiology

''Cladosporium sphaerospermum'' is considered a

saprotroph 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 (f ...

and is a secondary invader of dead or dying plant tissue. Energy is provided through the conversion of starch,

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

, and

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

and

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

. However, it has been shown in a laboratory environment that these fungi are able to successfully grow with

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) at ...

as the sole source of carbon. This trait may have arisen because these fungi and many others from the genus ''Cladosporium'' are secondary colonizers and frequently dwell in environments poor in nutrients. ''Cladosporium sphaerospermum'' is able to enhance

polycyclic aromatic hydrocarbon A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ...

biodegradation in soils due to reactive oxygen species produced as secondary

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...

s, such as H₂O₂. This species is a prolific producer of the pigmented secondary metabolite,

melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

, thought to serve as a protective mechanism against

UV irradiation Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses short-wavelength ultraviolet (ultraviolet C or UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unabl ...

, enzymatic lysis, oxidant attack, and fungal infections from other competing fungi. A method that can be used to determine the presence of this fungus on a background of other organic material is through the

KOH test The KOH Test for ''Candida albicans'', also known as a potassium hydroxide preparation or KOH prep, is a quick, inexpensive fungal test to differentiate dermatophytes and ''Candida albicans'' symptoms from other skin disorders like psoriasis and e ...

which stains the fungus. The addition of lactophenol blue with this test turns the

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

in the cell wall blue but leaves the budding

conidia 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 the ...

and globular

with their characteristic brown colouring. The first draft sequence of the ''C. sphaerospermum''

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 ge ...

was created in 2012. Genes were identified that are involved in the dihydroxynaphthalene (DHN)-

biosynthesis pathway which confirms the

etiology Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, e ...

of melanin in this species. Genes associated with the production of allergens were also identified as well as those conferring resistance to various antifungal drugs.

Habitat and ecology

''Cladosporium sphaerospermum'' is a

cosmopolitan Cosmopolitan may refer to: Food and drink * Cosmopolitan (cocktail), also known as a "Cosmo" History * Rootless cosmopolitan, a Soviet derogatory epithet during Joseph Stalin's anti-Semitic campaign of 1949–1953 Hotels and resorts * Cosmopoli ...

fungus that inhabits city buildings and the environment and because of its airborne nature it can move rapidly between locations, though the extent of this is lacking in research. It is found in hypersaline environments in

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

and tropical climates, as well as soil and plant environments in temperate climates. The indoor presence of this fungus can signify there is a

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...

problem within the building such as on bathroom walls and in kitchens. ''Cladosporium sphaerospermum'' is also been shown to inhabit paint films on walls and other surfaces as well as old paintings. This fungus is also able to grow on gypsum-based material with and without paint and wallpaper. Plant materials that are affected include citrus leaves on various other decaying plant leaves, on the stems of herbaceous and woody plants, on fruits and vegetables. The fungus has also been reported from wheat-based bakery items.

Human health

''Cladosporium sphaerospermum'' is mainly known as a spoilage agent of harvested fruits and vegetables. There are very few reports implicating this species as a disease agent in humans. It is known as an allergen and mainly causes problems in patients with respiratory tract diseases as well as subcutaneous

phaeohyphomycosis Phaeohyphomycosis is a diverse group of fungal infections, caused by dematiaceous fungi whose morphologic characteristics in tissue include hyphae, yeast-like cells, or a combination of these. It can be associated an array of melanistic filamento ...

and intrabronchial lesions in

immunocompetent In immunology, immunocompetence is the ability of the body to produce a normal immune response following exposure to an antigen. Immunocompetence is the opposite of immunodeficiency (also known as ''immuno-incompetence'' or being ''immuno-comprom ...

individuals caused by many dematiaceous fungi. It has been reported rarely from skin, eye, sinus, and brain infections. There has been one reported case in which a female patient developed swelling on the dorsum of her hand which, after testing with

Grocott's methenamine silver stain In pathology, the Grocott-Gomori's (or Gömöri) methenamine silver stain, abbreviated GMS, is a popular staining method in histology. The stain was originally named after György Gömöri, the Hungarian physician who developed the stain. It is ...

and Lactophenol cotton blue, confirmed the presence of dematiaceous hyphae compatible with ''C. sphaerospermum''. Another case in which identified was where it caused cerebral phaeohyphomycosis but this was treated successfully and the symptoms were abated. ''Cladosporium sphaerospermum'' produces allergenic compounds but is not known to produce significant

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' ...

Protection against radiation

An experiment has been made at the

International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...

in December 2018 and January 2019 to test whether radiotrophic fungi could be used as protection against radiation, especially in space. The experiment used Cladosporium sphaerospermum. Results were prepublished for

peer-review Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work (peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer review ...

in July 2020 .

References

{{taxonbar , from = Q10454504 Cladosporium Fungi described in 1882