Wallemiomycetes

The Wallemiomycetes are a class of fungi in the division Basidiomycota. It consists of the single order Wallemiales, containing the single family Wallemiaceae, which in turn contains the single genus Wallemia. The phylogenetic 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.[3][4] 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, halotolerance, chaotolerance, growth temperature regimes, extracellular enzyme activity profiles, and secondary metabolite patterns.[1][5] They are typically isolated from low-moisture foods (such as cakes, bread, sugar, peanuts, dried fish), indoor air dust, salterns and soil.[1] W. sebi is thought to be one of the causes of the hypersensitivity pneumonitis known as the farmer's lung disease,[6] but since the other species were recognised and separated from W. sebi only recently, their role in the disease cannot be excluded.[1]

Wallemiomycetes
Wallemia sebi
Wallemia sebi
Scientific classification
Kingdom:
Fungi
Division:
Basidiomycota
Class:
Wallemiomycetes

Zalar, de Hoog, & Schroers (2005)[1]
Order:
Wallemiales

Zalar, de Hoog, & Schroers (2005)
Family:
Wallemiaceae

Genus:
Wallemia

Type species
Wallemia ichthyophaga
Species

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 (unlike, for example, halophilic Archaea).[7] 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.[1]

Studies on Wallemia sebi showed that it produces numerous secondary metabolic compounds, including walleminol, walleminone, wallemia A and C, and azasteroid UCA1064-B.[8] A comprehensive research on other species of the class discovered that secondary metabolites 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.[9]

Cell wall and morphological changes of Wallemia species are thought to play a major role in adaptation to low water activity.[10]

The whole genome sequences of W. sebi[3] and W. ichthyophaga[4] are available.

References
  1. Zalar P, Sybren de Hoog G, Schroers HJ, Frank JM, Gunde-Cimerman N (May 2005). "Taxonomy and phylogeny of the xerophilic genus Wallemia (Wallemiomycetes and Wallemiales, cl. et ord. nov.)". Antonie van Leeuwenhoek. 87 (4): 311–28. doi:10.1007/s10482-004-6783-x. PMID 15928984. S2CID 4821447.
  2. Sneh B, Jabaji-Hare S, Neate S, Dijst G (1996). Rhizoctonia species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. Springer. p. 20. ISBN 978-0-7923-3644-0.
  3. Padamsee M, Kumar TK, Riley R, Binder M, Boyd A, Calvo AM, Furukawa K, Hesse C, Hohmann S, James TY, LaButti K, Lapidus A, Lindquist E, Lucas S, Miller K, Shantappa S, Grigoriev IV, Hibbett DS, McLaughlin DJ, Spatafora JW, Aime MC (March 2012). "The genome of the xerotolerant mold Wallemia sebi reveals adaptations to osmotic stress and suggests cryptic sexual reproduction". Fungal Genetics and Biology (Submitted manuscript). 49 (3): 217–26. doi:10.1016/j.fgb.2012.01.007. PMID 22326418.
  4. Zajc J, Liu Y, Dai W, Yang Z, Hu J, Gostinčar C, Gunde-Cimerman N (September 2013). "Genome and transcriptome sequencing of the halophilic fungus Wallemia ichthyophaga: haloadaptations present and absent". BMC Genomics. 14: 617. doi:10.1186/1471-2164-14-617. PMC 3849046. PMID 24034603.
  5. Jančič S, Nguyen HD, Frisvad JC, Zalar P, Schroers HJ, Seifert KA, Gunde-Cimerman N (2015-05-27). "A Taxonomic Revision of the Wallemia sebi Species Complex". PLOS ONE. 10 (5): e0125933. Bibcode:2015PLoSO..1025933J. doi:10.1371/journal.pone.0125933. PMC 4446336. PMID 26017053.
  6. Reboux G, Piarroux R, Mauny F, Madroszyk A, Millon L, Bardonnet K, Dalphin JC (June 2001). "Role of molds in farmer's lung disease in Eastern France". American Journal of Respiratory and Critical Care Medicine. 163 (7): 1534–9. doi:10.1164/ajrccm.163.7.2006077. PMID 11401869.
  7. Gostincar C, Grube M, de Hoog S, Zalar P, Gunde-Cimerman N (January 2010). "Extremotolerance in fungi: evolution on the edge". FEMS Microbiology Ecology. 71 (1): 2–11. doi:10.1111/j.1574-6941.2009.00794.x. PMID 19878320.
  8. Desroches TC, McMullin DR, Miller JD (October 2014). "Extrolites of Wallemia sebi, a very common fungus in the built environment". Indoor Air. 24 (5): 533–42. doi:10.1111/ina.12100. PMID 24471934.
  9. Jančič S, Frisvad JC, Kocev D, Gostinčar C, Džeroski S, Gunde-Cimerman N (30 December 2016). "Production of Secondary Metabolites in Extreme Environments: Food- and Airborne Wallemia spp. Produce Toxic Metabolites at Hypersaline Conditions". PLOS ONE. 11 (12): e0169116. Bibcode:2016PLoSO..1169116J. doi:10.1371/journal.pone.0169116. PMC 5201246. PMID 28036382.
  10. Kralj Kuncic M, Kogej T, Drobne D, Gunde-Cimerman N (January 2010). "Morphological response of the halophilic fungal genus Wallemia to high salinity". Applied and Environmental Microbiology. 76 (1): 329–37. Bibcode:2010ApEnM..76..329K. doi:10.1128/AEM.02318-09. PMC 2798636. PMID 19897760.
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