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. It consists of the single order Wallemiales, containing the single

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

Wallemiaceae, which in turn contains the single

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 ...

''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 Basidiomycota, but according to the analysis of a larger dataset it is a sister group of

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 cla ...

. 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 conidial 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 norma ...

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 hyperse ...

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 than basidomycetous 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 tempe ...

(unlike, for example, halophilic Archaea). 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), 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