The Wallemiomycetes are a

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

fungi 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 ...

in the division

Basidiomycota Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basi ...

. It consists of the single

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Wallemiales, containing the single

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Wallemiaceae, which in turn contains the single

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

''Wallemia''. The

phylogenetic 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 ...

origin of the lineage was placed to various parts of

, but according to the analysis of a larger dataset it is a

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

Agaricomycotina The subdivision Agaricomycotina, also known as the hymenomycetes, is one of three taxa of the fungal division Basidiomycota (fungi bearing spores on basidia). The Agaricomycotina contain some 20,000 species, and about 98% of these are in the clas ...

. The genus contains species of xerophilic molds that are found worldwide. The seven described species ('' W. sebi'', '' W. ichthyophaga'', '' W. muriae'', '' W. mellicola'', '' W. canadensis'', '' W. tropicalis'', and '' W. hederae'') are distinguished by

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 ...

l size,

xerotolerance A xerophile () is an extremophilic organism that can grow and reproduce in conditions with a low availability of water, also known as water activity. Water activity (aw) is measured as the humidity above a substance relative to the humidity above p ...

halotolerance 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 ...

, chaotolerance, growth temperature regimes, extracellular enzyme activity profiles, and

secondary metabolite Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animals, or plants, which are not directly involved in the norm ...

patterns. They are typically isolated from low-moisture foods (such as cakes, bread, sugar, peanuts, dried fish), indoor air dust, salterns and soil. ''W. sebi'' is thought to be one of the causes of the hypersensitivity pneumonitis known as the

farmer's lung Farmer's lung (not to be confused with silo-filler's disease) is a hypersensitivity pneumonitis induced by the inhalation of biologic dusts coming from hay dust or mold spores or any other agricultural products. It results in a type III hypersen ...

disease, but since the other species were recognised and separated from ''W. sebi'' only recently, their role in the disease cannot be excluded. Tolerance to low water activity is generally much more frequent among

ascomycetous Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The de ...

than

basidomycetous Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Bas ...

fungi, and xerotolerant fungi are also able to grow in regular growth media with normal

water activity Water activity (''aw'') is the partial vapor pressure of water in a solution divided by the standard state partial vapor pressure of water. In the field of food science, the standard state is most often defined as pure water at the same tempera ...

(unlike, for example, halophilic

Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

). However, species from the genus ''Wallemia'' are an exception to both of these rules: all species can tolerate high concentrations of sugars and salts (''W. ichthyophaga'' grows even in media saturated with

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...

), while ''W. muriae'' and ''W. ichthyophaga'' cannot be cultivated unless the water activity of the medium is lowered. Studies on ''Wallemia sebi'' showed that it produces numerous secondary metabolic compounds, including walleminol, walleminone, wallemia A and C, and azasteroid UCA1064-B. A comprehensive research on other species of the class discovered that

s are consistently produced by ''Wallemiomycetes'' and their production is – contrary to common presumptions – increased as a response to increasing NaCl concentration. In particular an increase in NaCl concentration from 5% to 15% in the growth media increased the production of the toxic metabolites wallimidione, walleminol and walleminone. Cell wall and morphological changes of ''Wallemia'' species are thought to play a major role in adaptation to low water activity. The whole genome sequences of '' W. sebi'' and ''W. ichthyophaga'' are available.

References

{{Taxonbar, from=Q10719182, from2=Q12269570, from3=Q10719180, from4=Q1138166, from5=Q10719181 Basidiomycota classes Monotypic fungus taxa