Survey of Genomes - Saccharomyces cerevisiae

Welcome to Genomic Revolution. This is Curtis Swearingen from the 2019 Hiram College Genetics course hosting this episode on the genome Saccharomyces cerevisiae S288C.  This strain is from the fungal division Ascomycota and the family Saccharomycetaceae.  Saccharomyces cerevisiae is an eukaryotic microbe. More specifically, it is a globular-shaped, yellow-green yeast belonging to the Fungi kingdom, which includes multicellular organisms such as mushrooms and molds.  Natural strains of the yeast have been found on the surfaces of plants, the gastrointestinal tracts and body surfaces of insects and warm-blooded animals, soils from all regions of the world and even in aquatic environments.  Most often it is found in areas where fermentation can occur, such as the on the surface of fruit, storage cellars and on the equipment used during the fermentation process.  S. cerevisiae is famously known for its role in food production. It is the critical component in the fermentation process that converts sugar into alcohol, an ingredient shared in beer, wine and distilled beverages.  It is also used in the baking process as a leavening agent; yeast releasing gas into their environment results in the spongy-like texture of breads and cakes.  Because of its role in fermentation, humans have known about and used S. cerevisiae for a long time.  Archaeologists have found evidence of a fermented beverage in a pot in China as early as 7000 BC, and molecular evidence of yeast being used in fermentation was found in a wine jar dating back to 3150 BC.  Isolation of the species did not occur until 1938, when Emil Mrak isolated it from rotten figs found in Merced, California.  Taking advantage of its unique reproductive cycle, in the 1950s Robert Mortimer performed genetic crosses that used the isolated fig strain and other yeast strains obtained through other researchers.  As a result, he created a new strain called S288c, which is the species strain we are talking about, which was then used as a parental strain in order to isolate most of the mutant strains currently used in research.  Furthermore, this strain was then used to sequence the S. cerevisiae genome.  The entire genome was sequenced 1996, being the first genome to be entirely sequenced.  12.068 Million bp are spread out across 16 chromosomes and codes for about 5885 proteins.  In the genome, 5,885 genes code for proteins, 275 code for tRNA, 40 code for snRNA's, and 140 genes code for ribosomal RNA.  4% of the genome is comprised of introns.  Out of all the genes that code for proteins, 11% of the protenome is devoted to metabolism, 3% to energy production and storage, 3% to DNA replication, 7% to transcription and 6% to translation.  Nearly 430 proteins are involved in intracellular trafficking, and 250 proteins have structural roles.

Because S. cerevisiae is a eukaryote, there are many cool things that scientists have done with it genetic information and genetic tools.  S. cerevisiae is an attractive model organism due to the fact that its genome has been sequenced, its genetics are easily manipulated, and it is very easy to maintain in the lab.  Previous studies performed in S. cerevisiae that have contributed to our understanding of important cellular processes such as the cell cycle, aging, and cell death.  They have also been used to make proteins to help combat Alzheimer’s and Parkinson’s diseases in humans.  Some cool facts on S. cerevisiae is that a heat tolerant strain of to be used to make ethanol and use that ethanol from the S. cerevisiae rather than from starch based plants because they are limited as a alternative to petroleum.  The strain of Saccharomyces can make 42g of ethanol with 97.4g of sugar, which is a 84.36% fermentation efficiency.  Hopefully one day we can stray away from the use of petroleum in the near future.  Another cool fact is because S. cerevisiae is a eukaryotic cell is has been used to make human insulin for those affected by diabetes.  With its help the global insulin market is expected to reach $70.6B by the year 2023.  With the help of Saccharomyces cerevisiae, it can allow for easier and cheaper access for people to essential proteins to maintain a healthy life.  One last cool fact is even though there are many beneficial things S. cerevisiae can do, with too much exposure to taking as a probiotic can cause sickness in people.  There was a case with 57 patients with the infection and 60% were in the ICU and it was detected that 26 patients were given S. cerevisiae as a probiotic and 17 patients died.  The use of S. cerevisiae should be reassessed, especially in patients that are ill or immunosuppressed. The chances
are still very low in getting the disease for humans.  S. cerevisiae is a cool species with its ability to make human proteins and help make energy efficient products. We have yet to find the full potential of this species and hopefully 
in the near future it can help us even more.  Thanks for listening.

WORK CITED
1.) Ballesta, Isabella. 2010, September 26. A Microbial Biorealm page on the genus Saccharomyces cerevisiae. 
https://microbewiki.kenyon.edu/index.php/Saccharomyces_cerevisiae

2.) Nielsen, Jens. “Production of of biopharmaceutical proteins by yeast: advances through metabolic engineering” Bioengineered vol. 4,4 (2012): 207-11.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3728191/

3.) Mason, Robert P and Flaviano Girorgini. “Modeling Huntington disease in yeast: perspectives and future directions” Prion vol. 5,4 (2011): 269-76.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4012407/

4.) Patricia Muñoz, Emilio Bouza, Manuel Cuenca-Estrella, Jose María Eiros, Maria Jesús Pérez, Mar Sánchez-Somolinos, Cristina Rincón, Javier Hortal, Teresa Peláez, Saccharomyces cerevisiae Fungemia: An Emerging Infectious Disease, Clinical Infectious Diseases, vol. 40,11 (2005) Pg. 1625–1634.  https://academic.oup.com/cid/article/40/11/1625/445600