Saccharomyces cerevisiae characteristics, morphology, life cycle

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Robert Johnston

The Saccharomyces cerevisiae or brewer's yeast is a species of unicellular fungus that belongs to the Ascomicota phylum, to the Hemiascomicete class and to the Saccharomycetales order. It is characterized by its wide distribution of habitats, such as leaves, flowers, soil, and water. Its name means beer sugar mushroom, because it is used during the production of this popular drink..

This yeast has been used for more than a century in baking and brewing, but it was in the early 20th century that scientists paid attention to it, making it a model for study..

Saccharomyces cerevisiae on agar plate. By Rainis Venta [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons

This microorganism has been widely used in different industries; It is currently a fungus widely used in biotechnology, for the production of insulin, antibodies, 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..

Article index

  • 1 Biological characteristics
  • 2 Morphology
  • 3 Life cycle
  • 4 Uses
    • 4.1 Pastries and bread
    • 4.2 Food supplement
    • 4.3 Manufacture of beverages
    • 4.4 Biotechnology
  • 5 References

Biological characteristics

Saccharomyces cerevisiae is a eukaryotic unicellular microbe, globular in shape, yellowish green. It is chemoorganotrophic, since it requires organic compounds as an energy source and does not require sunlight to grow. This yeast is capable of using different sugars, with glucose being the preferred carbon source.

S. cerevisiae is facultative anaerobic, as it is capable of growing in oxygen-deficient conditions. 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 S. cerevisiae has been completely sequenced, being the first eukaryotic organism to be achieved. The genome is organized into a haploid set of 16 chromosomes. Approximately 5,800 genes are destined for protein synthesis.

The S. cerevisiae genome 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 1035 reactions..

Morphology

S. cerevisiae is a small single-celled organism that is closely related to the cells of animals and plants. 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 the Golgi apparatus are involved in lipid synthesis and protein modification..

The vacuole and peroxisomes contain metabolic pathways related to digestive functions. Meanwhile, a complex scaffolding network acts as cell support and allows cell movement, thus performing the functions of the cytoskeleton..

The actin and myosin filaments of the cytoskeleton work through the use of energy and allow the polar ordering of cells during cell division..

Cell division leads to asymmetric cell division, resulting in a larger stem cell than the daughter cell. This is very common in yeasts and is a process that is defined as budding..

S. cerevisiae has a chitin cell wall, giving yeast its characteristic cell shape. This wall prevents osmotic damage since it exerts turgor pressure, giving these microorganisms a certain plasticity in harmful environmental conditions. Cell wall and membrane are connected by periplasmic space.

Lifecycle

Saccharomyces cerevisiae sexual cycle. Source: Wikimedia Commons

The life cycle of S. cerevisiae is similar to that of most somatic cells. Both 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, haploid cell culture reproduces faster than diploid cell culture. Haploid cells have buds that appear adjacent to the previous ones, while diploid cells appear at opposite poles.

Vegetative growth occurs by budding, in which the daughter cell begins as a bud from the mother 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 meiosis process, producing four spores (ascas). These spores have high resistance and can germinate in a rich medium.

The spores can be of the mating group a, α or both, this being analogous to 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, each one forms a kind of protuberance that, when joining, eventually leads to intercellular contact, ultimately producing a diploid cell..

Applications

Pastries and bread

S. cerevisiae is the yeast most used by humans. One of the main uses has been in baking and bread making, since during the fermentation process, the wheat dough softens and expands..

Nutritional supplement

On the other hand, this yeast has been used as a dietary supplement, because about 50% of its dry weight is made up of proteins, it is also rich in vitamin B, niacin and folic acid.

Manufacture of beverages

This yeast is involved in the production of different beverages. The brewing industry uses it extensively. By fermenting the sugars that make up the barley grains, beer, a world popular drink, can be produced.

Similarly, S. cerevisiae can ferment the sugars present in grapes, producing up to 18% ethanol by volume of wine..

Biotechnology

On the other hand, from the biotechnological point of view, S. cerevisiae has been a model of study and use, because it is an organism that is easy to grow, fast growing and whose genome has been sequenced.

The use of this yeast by the biotechnology 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 biotechnology factories have displaced petrochemical factories in the production of chemical compounds..

References

  1. Harwell, L.H., (1974). Saccharomyces cerevisiae cell cycle. Bacteriological reviews, 38 (2), pp. 164-198.
  2. Karithia, H., Vilaprinyo, E., Sorribas, A., Alves, R., (2011). PLoS ONE, 6 (2): e16015. doi.org.
  3. Kovačević, M., (2015). Morphological and physiological characteristics of the yeast Saccharomyces cerevisiae cells differing in the life span. Master's Thesis in Biochemistry. Faculty of Pharmacy and Biochemistry, University of Zagreb. Zagreb-Croatia.
  4. Otero, J. M., Cimini, D., Patil, K. R., Poulsen, S. G., Olsson, L., Nielsen, J. (2013). Industrial Systems Biology of Saccharomyces cerevisiae Enables Novel Succinic Acid Cell Factory. PLoS ONE, 8 (1), e54144. http://doi.org/10.1371/journal.pone.0054144
  5. Saito, T., Ohtani, M., Sawai, H., Sano, F., Saka, A., Watanabe, D., Yukawa, M., Ohya, Y., Morishita, S., (2004). Saccharomyces cerevisiae morphological database. Nucleic Acids Res, 32, pp. 319-322. DOI: 10.1093 / nar / gkh113
  6. Shneiter, R., (2004). Genetics, molecular and cell biology of yeast. Université de Friborg Suisse, pp. 5-18.

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