Nguyen & Gaillardin ex. Beijerinck
Saccharomyces pastorianus is a yeast used industrially for the production of lager beer, and is named after Louis Pasteur. It is a synonym of the yeast species Saccharomyces carlsbergensis, which was originally described in 1883 by Emil Christian Hansen, who was working for the Danish brewery Carlsberg.
S. pastorianus is an interspecific hybrid between Saccharomyces eubayanus  and Saccharomyces cerevisiae, and has a degree of phenotypic and genomic similarity between the two species. The hybrid nature of S. pastorianus also explains the genome size, which is up to 60% larger than that of S. cerevisiae, as it includes large parts of the two genomes. There is growing evidence, however, that S. pastorianus has inherited most of its genetic material from an S. bayanus-like yeast. Indeed the mitochondrial DNA and ribosomal DNA of S. pastorianus appear to be derived from the S. bayanus-like parental strain rather than S. cerevisiae.
The genomic difference between S. pastorianus and S. cerevisiae is responsible for a number of phenotypic traits which S. pastorianus shares with S. bayanus, but not S. cerevisiae. The ability of S. pastorianus to break down melibiose is dependent on up to ten MEL genes, which are exclusive to strains metabolising melibose such as S. bayanus. S. pastorianus never grows above 34 °C (93 °F), whereas S. cerevisiae will grow at 37 °C (99 °F). S. pastorianus exhibits a higher growth rate than S. cerevisiae at 6 to 12°C.
S. pastorianus has been suggested as a hybrid of S. cerevisiae and S. monacensis, as the LEU2, MET2 and ACB1 genes of S. pastorianus had been reported to have a high level of similarity or be identical to the S. monacensis homologues. However, subtelomeric sequence hybridisation has suggested S. monacensis is likely to be a closely related hybrid to S. pastorianus, rather than an ancestor.
Ale strains are genetically more diverse than lager strains, as lager strains are thought to derive from a hybrid gene pool. The lager strains in use are thought to derive from only one or two primary strains, Tuborg and Carlsberg.
The yeast species Saccharomyces uvarum is believed to have originated as a hybrid of S. cerevisiae and S. monacensis, because of its allopolyploid genome. It is a bottom-fermenting yeast, so-called because it does not form the foam on top of the wort as top-fermenting yeast does.
- Casaregola, S.; et al. (2001), Analysis of the constitution of the beer yeast genome by PCR, sequencing and subtelomeric sequence hybridization, International Journal of Systematic and Evolutionary Microbiology 51 (4): 1607–1618.
- "Louis Pasteur and Carlsberg Cure the 'Beer Disease' - Carlsberg Group company history page". Carlsberggroup.com. Retrieved 30 March 2013.
- Libkind, D.; Hittinger, C.; Valério, E.; Gonçalves, C.; Dover, J.; Johnston, M; Gonçalves, P.; Sampaio, J. (2011), Microbe domestication and the identification of the wild genetic stock of lager-brewing yeast, PNAS.
- Tamai, Y.; Momma, T.; Yoshimoto, H.; Kaneko, Y. (1998), Co-existence of two types of chromosome in the bottom fermenting yeast, Saccharomyces pastorianus, Yeast 14 (10): 923–933, doi:10.1002/(SICI)1097-0061(199807)14:10<923::AID-YEA298>3.0.CO;2-I.
- Montrocher, R.; et al. (1998), Phylogenetic analysis of the Saccharomyces cerevisiae group based on polymorphisms of rDNA spacer sequences, International Journal of Systematic Bacteriology 48 (1): 295–303, doi:10.1099/00207713-48-1-295.
- Piskur, J.; Smole, S.; Groth, C.; Petersen, R. F. & Pedersen, M. B. (1998), Structure and genetic stability of mitochondrial genomes vary among yeasts of the genus Saccharomyces, International Journal of Systematic Bacteriology 48 (3): 1015–1024, doi:10.1099/00207713-48-3-1015.
- Hansen, J. & Kielland-Brandt, M. C. (1994), Saccharomyces carlsbergensis contains two functional MET2 alleles similar to homologues from S. cerevisiae and S. monacensis, Gene 140 (1): 33–40, doi:10.1016/0378-1119(94)90727-7, PMID 8125336.
- Casey, G. P.; Pedersen, M. B. (1988), DNA sequence polymorphisms in the genus Saccharomyces. V. Cloning and characterization of aLEU2 gene from S. carlsbergensis, Carlsberg Research Communications 53 (3): 209–219, doi:10.1007/BF02904408.
- Borsting, C.; et al. (1997), Saccharomyces carlsbergensis contains two functional genes encoding the acyl-CoA binding protein, one similar to the ACB1 gene from S. cerevisiae and one identical to the ACB1 gene from S. monacensis, Yeast 13 (15): 1409–1421, doi:10.1002/(SICI)1097-0061(199712)13:15<1409::AID-YEA188>3.0.CO;2-A.
- Casey, Gregory P. (1996). "Practical applications of pulsed field electrophoresis and yeast chromosome fingerprinting of brewing QA and R&D". Technical Quarterly of the Masters Brewers Association of the Americas 33: 1–10.
- Casey, Gregory; Pringle, A.T.; Erdmann, P.A. (1990). "Evaluation of Recent Techniques Used to Identify Individual Strains of Saccharomyces Yeasts". J. Am. Soc. Brew. Chem. 48 (0100). doi:10.1094/ASBCJ-48-0100.
- Nguyen, H. V. & Gaillardin, C. (2005), Evolutionary relationships between the former species Saccharomyces uvarum and the hybrids Saccharomyces bayanus and Saccharomyces pastorianus; reinstatement of Saccharomyces uvarum (Beijerinck) as a distinct species, FEMS Yeast Research 5 (4–5): 471–483, doi:10.1016/j.femsyr.2004.12.004.
- Saccharomyces uvarum at EPA.gov