''Wallemia mellicola'' is a xerophilic fungus of the phylum

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 ...

, described in 2015 upon taxonomic revision of the species ''

Wallemia sebi ''Wallemia sebi'' is a xerophilic fungus of the phylum Basidiomycota. It is commonly found on highly sugared or salted materials, such as jams, bread, cakes, sugar, bacon, salted meats, and salted fish. It is also found in indoor air, house du ...

''. A large amount of published research referring to ''W. sebi'' was likely actually performed on ''W. mellicola''. An example of this is the sequencing of the ''W. mellicola'' genome, which was published under the name of ''W. sebi''. It has a worldwide distribution and is often found in habitats with low accessibility of water, from food preserved with high concentrations of sugar, salt or with drying, to dried straw and house dust. It has rarely been reported as the cause of human infections. Like other species of the same genus, ''W. mellicola'' grows at low

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 ...

, however it is not obligately xerophilic and can grow without additional solute in the growth medium. It grows at salt concentrations up to 24% NaCl, 13% MgCl₂ and at temperatures between 10 °C and 34 °C. ''W. mellicola'' has a compact genome of 9.8 Mb with few repeats, which is one of the smallest genomes in

and in Agaricomycota. Three gene family expansions that were observed in ''W. mellicola'' were considered significant, including

heat shock protein Heat shock proteins (HSP) are a family of proteins produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock, but are now known to also be expressed during other stresses including expo ...

, stress responsive alpha-beta barrel, and

amino acid transporter An amino acid transporter is a membrane transport protein that transports amino acids. They are mainly of the solute carrier family. Families There are several families that function in amino acid transport, some of these include: TC# 2.A.3- ...

, and they may be responsible for the survival ''W. mellicola'' at low water activity. Genes involved in High Osmolarity Glycerol signalling pathway were also found and were suggested to play an important role in the adaptation to osmotic stress. ''Wallemia mellicola'' also have a large number of transporters that allow it to survive in

hyperosmotic In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane- ...

conditions. After sequencing the genomes of additional 25 strains of ''W. mellicola'', these was found to form a relatively homogeneous and widespread population. According to population genomic data the species is at least occasionally recombining. Two versions of a putative mating-type locus have been found in the sequenced genomes, each present in approximately half of the strains.

References

{{Taxonbar, from=Q101242816 Wallemiales Fungi described in 2015