Hortaea werneckii

Hortaea werneckii is a species of yeast in the family Teratosphaeriaceae.[1] It is a black yeast that is investigated for its remarkable halotolerance.[2][3] While the addition of salt to the medium is not required for its cultivation, H. werneckii can grow in close to saturated NaCl solutions.[4] To emphasize this unusually wide adaptability, and to distinguish H. werneckii from other halotolerant fungi, which have lower maximum salinity limits, some authors describe H. werneckii as "extremely halotolerant".[4]

Hortaea werneckii
Micrograph of the fungus Hortaea werneckii
Scientific classification
Kingdom:
Fungi
Division:
Ascomycota
Class:
Dothideomycetes
Order:
Capnodiales
Family:
Teratosphaeriaceae
Genus:
Hortaea
Species:
H. werneckii
Binomial name
Hortaea werneckii
(Horta) Nishim. & Miyaji (1984)

Several salt-tolerance mechanisms of H. werneckii have been studied on molecular level.[4] For example, it is known that its major compatible solutes are glycerol, erythritol, arabitol, and mannitol; melanin accumulation of the cell wall aids in retention of at least glycerol inside of the cell.[3] Several components of the high osmolarity glycerol (HOG) signalling pathway (which controls responses to osmotic shock) have been studied in detail and some seem to differ in function compared to their counterparts in Saccharomyces cerevisiae.[5][6][7] Adaptation to high concentrations of salt are also accompanied by changes in membrane lipid composition, mainly by increasing the unsaturation of the phospholipid fatty acids.[8][9]

H. werneckii causes a rare superficial and non-invasive skin infection Tinea nigra.[10] The typical symptoms are non-scaly, smooth, brown-black painless spots on the palms of hands and soles of feet.

The growth of H. werneckii in liquid media is often yeast-like, although it can switch to filamentous growth. The mechanism of the switch is not known. The cells appear brown because of melanin production.[3]

Whole genome sequencing of H. werneckii[11][12] revealed a recent whole genome duplication, thought to be the only reported whole-genome duplication among ascomycetous yeasts besides the better known one in the Saccharomyces cerevisiae lineage.[13] Based on genome sequencing of additional strains, 10 out of 12 strains have a genome that was duplicated by several hybridizations between haploid strains, yielding formed stable diploids. Apart from these hybridization events, no signs of sexual reproduction were found.[14] As a consequence, the genome of H. werneckii is relatively large (49.9 Mb) with 15974 predicted genes.[12] Genes encoding metal cation transporters, which are thought to play a role in halotolerance, experienced several additional gene duplications at various points during their evolution.[11]

A homothallic mating locus was found in all sequenced genomes, although one of the mating genes may have been inactivated in some strains. Despite this, phylogenetic analyses and linkage disequilibrium analyses indicate that H. werneckii is asexual.[14]

References
  1. "Archived copy". Archived from the original on 2009-08-21. Retrieved 2009-08-10.CS1 maint: archived copy as title (link)
  2. Gunde-Cimerman N, Ramos J, Plemenitas A (November 2009). "Halotolerant and halophilic fungi". Mycological Research. 113 (Pt 11): 1231–41. doi:10.1016/j.mycres.2009.09.002. PMID 19747974.
  3. Kogej T, Stein M, Volkmann M, Gorbushina AA, Galinski EA, Gunde-Cimerman N (December 2007). "Osmotic adaptation of the halophilic fungus Hortaea werneckii: role of osmolytes and melanization". Microbiology. 153 (Pt 12): 4261–73. doi:10.1099/mic.0.2007/010751-0. PMID 18048939.
  4. Gostinčar C, Lenassi M, Gunde-Cimerman N, Plemenitaš A (2011). "Fungal adaptation to extremely high salt concentrations". Advances in Applied Microbiology. 77: 71–96. doi:10.1016/B978-0-12-387044-5.00003-0. PMID 22050822.
  5. Turk M, Plemenitas A (November 2002). "The HOG pathway in the halophilic black yeast Hortaea werneckii: isolation of the HOG1 homolog gene and activation of HwHog1p". FEMS Microbiology Letters. 216 (2): 193–9. doi:10.1111/j.1574-6968.2002.tb11435.x. PMID 12435502.
  6. Lenassi M, Vaupotic T, Gunde-Cimerman N, Plemenitas A (March 2007). "The MAP kinase HwHog1 from the halophilic black yeast Hortaea werneckii: coping with stresses in solar salterns". Saline Systems. 3: 3. doi:10.1186/1746-1448-3-3. PMC 1828057. PMID 17349032.
  7. Fettich M, Lenassi M, Veranič P, Gunde-Cimerman N, Plemenitaš A (May 2011). "Identification and characterization of putative osmosensors, HwSho1A and HwSho1B, from the extremely halotolerant black yeast Hortaea werneckii". Fungal Genetics and Biology. 48 (5): 475–84. doi:10.1016/j.fgb.2011.01.011. PMID 21281727.
  8. Turk M, Méjanelle L, Sentjurc M, Grimalt JO, Gunde-Cimerman N, Plemenitas A (February 2004). "Salt-induced changes in lipid composition and membrane fluidity of halophilic yeast-like melanized fungi". Extremophiles. 8 (1): 53–61. doi:10.1007/s00792-003-0360-5. PMID 15064990.
  9. Gostincar C, Turk M, Plemenitas A, Gunde-Cimerman N (March 2009). "The expressions of Delta 9-, Delta 12-desaturases and an elongase by the extremely halotolerant black yeast Hortaea werneckii are salt dependent". FEMS Yeast Research. 9 (2): 247–56. doi:10.1111/j.1567-1364.2009.00481.x. PMID 19220869.
  10. Reid BJ (July 1998). "Exophiala werneckii causing tinea nigra in Scotland". The British Journal of Dermatology. 139 (1): 157–8. doi:10.1046/j.1365-2133.1998.02340.x. PMID 9764175.
  11. Lenassi M, Gostinčar C, Jackman S, Turk M, Sadowski I, Nislow C, Jones S, Birol I, Cimerman NG, Plemenitaš A (2013). "Whole genome duplication and enrichment of metal cation transporters revealed by de novo genome sequencing of extremely halotolerant black yeast Hortaea werneckii". PLOS One. 8 (8): e71328. doi:10.1371/journal.pone.0071328. PMC 3744574. PMID 23977017.
  12. Sinha S, Flibotte S, Neira M, Formby S, Plemenitaš A, Cimerman NG, Lenassi M, Gostinčar C, Stajich JE, Nislow C (July 2017). "Hortaea werneckii: Combining an Improved Genome with Gene Expression and Chromatin Structure". G3. 7 (7): 2015–2022. doi:10.1534/g3.117.040691. PMC 5499112. PMID 28500048.
  13. Dujon B (August 2015). "Basic principles of yeast genomics, a personal recollection". FEMS Yeast Research. 15 (5): fov047. doi:10.1093/femsyr/fov047. PMID 26071597.
  14. Gostinčar C, Stajich JE, Zupančič J, Zalar P, Gunde-Cimerman N (May 2018). "Genomic evidence for intraspecific hybridization in a clonal and extremely halotolerant yeast". BMC Genomics. 19 (1): 364. doi:10.1186/s12864-018-4751-5. PMC 5952469. PMID 29764372.
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