por What is Saccharomyces cerevisiae?
Saccharomyces cerevisiae Brewer’s yeast is a species of unicellular fungus that belongs to the Ascomycota phylum, the Hemiascomycete class, and the Saccharomicetales order. It is characterized by its wide distribution of habitats, such as leaves, flowers, soil and water. Its name means beer sugar mushroom, as it is used during the production of this popular drink.
This yeast has been used for more than a century in confectionery and in the manufacture of beer, but it was at the beginning of the 20th century that scientists paid attention to it, turning it into a study model.
This microorganism has been widely used in different industries; It is currently a fungus widely used in biotechnology for the production of insulin, antibodies, or albumin, among other substances of interest to humanity.
As a study model, this yeast has made it possible to elucidate the molecular mechanisms that occur during the cell cycle in eukaryotic cells.
Characteristics of Saccharomyces cerevisiae
Saccharomyces cerevisiae It is a unicellular eukaryotic microbe, globular in shape, yellowish green. It is a chemoorganotroph, since it requires organic compounds as a source of energy and does not require sunlight to grow.
This yeast is capable of using different sugars, glucose being the preferred carbon source.
Saccharomyces cerevisiae It is facultative anaerobic, that is, it is capable of growing in conditions of oxygen deficiency. During this environmental condition, glucose is converted into different intermediates such as ethanol, CO₂, and glycerol.
The latter is known as alcoholic fermentation. During this process, the growth of the yeast is not efficient, however, it is the medium widely used by the industry to ferment the sugars present in different grains, such as wheat, barley and corn.
The genome of Saccharomyces cerevisiae It has been completely sequenced, being the first eukaryotic organism to be achieved. The genome is organized in a haploid set of 16 chromosomes. Approximately 5,800 genes are destined for protein synthesis.
The genome of Saccharomyces cerevisiae it is very compact, unlike other eukaryotes, since 72% is represented by genes. Within this group, approximately 708 have been identified as participating in metabolism, carrying out about 1,035 reactions.
Morphology of Saccharamyces cerevisiae
Saccharomyces cerevisiae It is a small, single-celled organism that is closely related to animal and plant cells. The cell membrane separates the cellular components from the external environment, while the nuclear membrane protects the hereditary material.
As in other eukaryotic organisms, the mitochondrial membrane is involved in energy generation, while the endoplasmic reticulum (ER) and Golgi apparatus are involved in lipid synthesis and protein modification.
The vacuole and peroxisomes enclose metabolic pathways related to digestive functions. Meanwhile, a complex network of scaffolding acts as cell support and allows cell movement, thus performing cytoskeletal functions.
The actin and myosin filaments of the cytoskeleton function through the use of energy and allow the polar ordering of cells during cell division.
Cell division leads to asymmetric division of cells, resulting in a mother cell that is larger than the daughter cell. This is very common in yeasts, and it is a process that is defined as budding.
Saccharomyces cerevisiae it has a chitin cell wall, giving yeast its characteristic cell shape.
This wall prevents osmotic damage since it exerts turgor pressure, providing these microorganisms with a certain plasticity in harmful environmental conditions. The cell wall and the membrane are connected by the periplasmic space.
life cycle of Saccharamyces cerevisiae
The life cycle of Saccharomyces cerevisiae It is similar to that of most somatic cells. Haploid and diploid cells can exist. The cell size of haploid and diploid cells varies according to the growth phase and from strain to strain.
During exponential growth, the haploid cell culture reproduces faster than the diploid cell culture. Haploid cells have buds that appear adjacent to the previous ones, while in diploid cells they appear at opposite poles.
Vegetative growth occurs by budding, in which the daughter cell begins as a bud from the parent cell, followed by nuclear division, cell wall formation, and finally cell separation.
Each stem cell can form about 20-30 buds, so its age can be determined by the number of scars on the cell wall.
Diploid cells that grow without nitrogen and without a carbon source undergo a process of meiosis, producing four spores (asci). These spores have high resistance and can germinate in a rich medium.
Spores may be of mating group a, α, or both, this being the analogue of sex in higher organisms. Both cell groups produce pheromone-like substances that inhibit the cell division of the other cell.
When these two cell groups meet, they each form a kind of bulge, and upon joining, eventually intercellular contact occurs, ultimately producing a diploid cell.
Uses of Saccharamyces cerevisiae
pastries and bread
Saccharomyces cerevisiae It is the yeast most used by humans. One of the main uses has been in confectionery and in the manufacture of bread, since during the fermentation process, the wheat dough softens and expands.
Nutritional supplement
On the other hand, this yeast has been used as a food supplement, because about 50% of its dry weight is made up of proteins, and it is also rich in B vitamins, niacin and folic acid.
beverage manufacturing
This yeast is involved in the production of different beverages. The brewing industry uses it extensively. By fermenting the sugars that make up barley grains, beer can be produced, one of the oldest drinks in human history.
In the same way, Saccharomyces cerevisiae it can ferment the sugars present in the grapes, producing up to 18% ethanol per volume of wine.
Biotechnology
On the other hand, from the biotechnological point of view, Saccharomyces cerevisiae It has been a model for study and use, because it is an organism that is easy to cultivate, fast-growing, and whose genome has been sequenced.
The use of this yeast by the biotech industry ranges from the production of insulin to the production of antibodies and other proteins used by medicine.
Currently, the pharmaceutical industry has used this microorganism in the production of various vitamins, so biotechnological factories have displaced petrochemical factories in the production of chemical compounds.
References
Harwell, LH, (1974). Saccharomyces cerevisiae cell cycle. Bacteriological reviews, 38 (2), pp. 164-198.
Karithia, H., Vilaprinyo, E., Sorribas, A., Alves, R., (2011). PLOS ONE, 6(2): e16015. doi.org.
Shneiter, R., (2004). Genetics, molecular and cell biology of yeast. University of Friborg Suisse, pp. 5-18.