Yeasts are a group of eukaryotic microfungi with a well‐defined cell wall whose growth is either entirely unicellular or a combination of hyphal and unicellular reproduction. The approximately 1500 known yeast species belong to two distinct fungal phyla, the Ascomycota and the Basidiomycota. Within each of these phyla, yeasts can be found in several subphyla or classes, reflecting the enormous diversity of their evolutionary origins and biochemical properties. In nature, yeasts are found mainly in association with plants or animals but are also present in soil and aquatic environments. Yeasts grow rapidly and have simple nutritional requirements, for whieh reason they have been used as model systems in biochemistry, genetics and molecular biology. They were the first microorganisms to be domesticated for the production of beer, bread or wine, and they continue to be used for the benefit of humanity in the production of many important health care and industrial commodities, including recombinant proteins, biopharmaceuticals, biocontrol agents and biofuels. The best‐known yeast is the species Saccharomyces cerevisiae, which may be regarded as the world's foremost industrial microbe.

Key Concepts

  • Yeasts share in common a primarily unicellular mode of reproduction.
  • Yeasts are phylogenetically diverse, being classified in several classes of two fungal phyla.
  • The concept of yeast is rooted in history and does not always follow logical biological lines.
  • Yeasts have a rigid cell wall primarily made up of β‐(1–3)‐glucan.
  • Sexual reproduction in yeasts involves the formation of internally formed ascospores or externally formed basidiospores.
  • Current yeast classification is based on phylogenetic relationships inferred by gene sequencing.
  • Yeasts grow in nature primarily in association with the plant–insect interface or with warm‐blooded animals, but also occur in soil and aquatic habitats.
  • Yeasts serve as important industrial model systems in research.
  • Yeasts are of great importance in biotechnology. The main products are alcohol, yeast biomass and recombinant proteins. Saccharomyces cerevisiae is the premier industrial microorganism.
  • A few yeast species cause infections in humans and other animals, but most yeasts act in an opportunistic manner, in individuals that are immunocompromised.

Keywords: reproduction; fungi; systematics; ecology; application; biotechnology; genetics; spores; budding

Figure 1. Blastoconidia. Well‐developed pseudohyphae; all cells are formed by budding, remaining attached to each other and forming a treelike structure; the lateral and terminal cells are called blastoconidia or blastospores.
Figure 2. Apiculate cells. Ontogeny or development of characteristic cell shapes in an apiculate yeast (e.g. Hanseniaspora) from oval to apiculate during repeated bipolar budding.
Figure 3. Arthroconidia. A hyphal (filamentous) cell undergoing fission or cross wall (septum) formation and breaking up into individual cells called arthroconidia or arthrospores (e.g. Trichosporon).
Figure 4. Ballistospores. Formation of an asymmetric ballistoconidium or ballistospore on a pointed stalk or sterigma on a mother cell of a Sporobolomyces species. The asexual ballistospore is discharged forcefully by means of a droplet mechanism (arrows).
Figure 5. Life cycle of Rhodosporidium. Simplified life cycle of a heterothallic species of Rhodosporidium: K, karyogamy; P, plasmogamy; RD, reduction division (meiosis).
Figure 6. Life cycle of Filobasidium. Schematic life cycle of a heterothallic species of Filobasidium: K, karyogamy; P, plasmogamy; RD, reduction division (meiosis).


Banno I (1967) Studies on the sexuality of Rhodotorula. Journal of General Applied Microbiology 13: 167–169.

Barnett JA (2007) A history of research on yeasts 10: foundations of yeast genetics. Yeast 24: 799–845.

Bing J, Han PJ, Liu WQ, Wang QM and Bai FY (2014) Evidence for a Far East Asian origin of lager beer yeast. Current Biology 24 (10): R300‐1.

Botha A (2011) The importance and ecology of yeasts in soil. Soil Biology and Biochemistry 43: 1–8.

Cameron DE, Bashor CJ and Collins JJ (2014) A brief history of synthetic biology. Nature Reviews. Microbiology 12: 381–390.

Deparis Q, Claes A, Foulquié‐Moreno MR and Thevelein JM (2017) Engineering tolerance to industrially relevant stress factors in yeast cell factories. FEMS Yeast Research 17. DOI: 10.1093/femsyr/fox036.

Feldman H (2012) Yeast. Molecular and Cell Biology. Weinheim: Wiley‐Blackwell.

Gadanho M and Sampaio JP (2005) Occurrence and diversity of yeasts in the mid‐Atlantic Ridge hydrothermal fields near the Azores archipelago. Microbial Ecology 50: 408–417.

Ginns J and Malloch DW (2003) Filobasidiella depauperata (Tremellales): haustorial branches and parasitism of Verticillium lecanii. Mycological Progress 2: 137–140.

Golubev WI (1998) Mycocins (killer toxins). In: Kurtzman CP and Fell JW (eds) The Yeasts, A Taxonomic Study, 4th edn, pp. 55–62. Elsevier: Amsterdam.

Hagler AN and Ahearn DG (1987) Ecology of aquatic yeasts. In: Rose AH and Harrison JS (eds) The Yeasts, Biology of Yeasts, 2nd edn, vol. 1, pp. 181–205. London: Academic Press.

Herrera CM and Pozo MI (2010) Nectar yeasts warm the flowers of a winter‐blooming plant. Proceedings of the Royal Society B Biological Science 277: 1827–1834.

Liu Z, Ho SH, Sasaki K, et al. (2016) Engineering of a novel cellulose‐adherent cellulolytic Saccharomyces cerevisiae for cellulosic biofuel production. Scientific Reports 6: 24550.

Mans R and van Rossum HM, Wijsman M, et al. (2015) CRISPR/Cas9: a molecular Swiss army knife for simultaneous introduction of multiple genetic modifications in Saccharomyces cerevisiae. FEMS Yeast Research 15 (2): fov004.

Muccilli S and Restuccia C (2015) Bioprotective role of yeasts. Microorganisms 3: 588–611.

van der Klei I, Veenhuis M, Brul S, et al. (2011) Cytology, cell walls and septa: a summary of yeast cell biology from a phylogenetic perspective. In: Kurtzman CP, Fell JW and Boekhout T (eds) The Yeasts, A Taxonomic Study, 5th edn, pp. 111–128. Amsterdam: Elsevier.

Knight RD, Landweber LF and Yarus M (2001) How mitochondria redefine the code. Journal of Molecular Evolution 53: 299–313.

Kurtzman CP and Robnett CJ (1998) Identification and phylogeny of ascomycetous yeasts from analysis of nuclear large subunit (26S) ribosomal DNA partial sequences. Antonie Van Leeuwenhoek 73: 331–371.

Kurtzman CP, Fell JW and Boekhout T (eds) (2011) The Yeasts, a Taxonomic Study, 5th edn. Amsterdam: Elsevier.

Lachance MA, Pupovac‐Velikonja A, Natarajan S and Schlag‐Edler B (2000) Nutrition and phylogeny of predacious yeasts. Canadian Journal of Microbiology 46: 495–505.

Libkind D, Hittinger CT, Valério E, et al. (2011) Microbe domestication and the identification of the wild genetic stock of lager‐brewing yeast. Proceedings of the National Academy of Sciences of the United States of America 108: 14539–14544.

Peris D, Sylvester K, Libkind D, et al. (2014) Population structure and reticulate evolution of Saccharomyces eubayanus and its lager‐brewing hybrids. Molecular Ecology 23: 2031–2045.

Phaff HJ and Starmer WT (1987) Yeasts associated with plants, insects and soil. In: Rose AH and Harrison JS (eds) The Yeasts, Biology of Yeasts, 2nd edn, vol. 1, pp. 123–180. London: Academic Press.

Pretorius IS (2016) Conducting wine symphonics with the aid of yeast genomics. Beverages 2 (4): 36. DOI: 10.3390/beverages2040036.

Romanos MA, Scorer CA and Clare JJ (1992) Foreign gene expression in yeast: a review. Yeast 8: 423–488.

Sampaio P and Gonçalves P (2008) Natural populations of Saccharomyces kudriavzevii in Portugal are associated with oak bark and are sympatric with S. cerevisiae and S. paradoxus. Applied and Environmental Microbiology 74: 2144–2152.

Stewart GG (2016) Saccharomyces species in the production of beer. Beverages 2 (4): 34. DOI: 10.3390/beverages2040034.

Walker GM, Abbas C, Ingledew WM and Pilgrim C (eds) (2017) The Alcohol Textbook, 6th edn. Duluth, MN: Ethanol Technology Institute, 592 pp, ISBN 978‐0‐692‐93088‐5.

Walker GM and Stewart GG (2016) Saccharomyces cerevisiae in the production of fermented beverages. Beverages (2): 30. DOI: 10.3390/beverages2040030.

Further Reading

Barker JSF and Starmer WT (eds) (1982) Ecological Genetics and Evolution, The Cactus‐Yeast‐Drosophila Model System. Sydney: Academic Press.

Deâk T (2008) Handbook of Food Spoilage Yeasts, 2nd edn. Boca Raton, FL: CRC Press.

DeHoog GS, Smith MTH and Weijman ACM (eds) (1987) The expanding realm of yeast‐like fungi. In: Studies in Mycology. Amsterdam: Elsevier.

Lachance MA (2003) The Phaff School of Yeast Ecology. International Microbiology 6: 163–167.

Mapelli V (2014) Yeast Metabolic Engineering: Methods and Protocols. New York: Springer, pp. 313. ISBN:978‐1‐4939‐0562‐1.

Money NP (2018) The Rise of Yeast: How the Sugar Fungus Shaped Civilization. Oxford: Oxford University Press.

Phaff HJ, Miller MW and Mrak EM (1978) The Life of Yeasts, 2nd edn. Cambridge, MA: Harvard University Press.

Querol A and Fleet GH (2006) Yeasts in Food and Beverages. Berlin: Springer‐Verlag.

Rosa CA and Péter G (eds) (2006) The Yeast Handbook: Biodiversity and Ecophysiology of Yeasts. Berlin, Heidelberg: Springer.

Starmer WT, Lachance MA, Phaff HJ and Heed WB (1990) The biogeography of yeasts associated with decaying cactus tissue in North America, the Caribbean and Northern Venezuela. Evolutionary Biology 24: 253–296.

Walker G (1998) Yeast Physiology and Biotechnology. Chichester: Wiley.

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Lachance, Marc‐André, and Walker, Graeme M(Oct 2018) Yeasts. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000380.pub3]