Saccharomyces

SOIL MICROBIOLOGY

BIOL/CSES 4684

This webpage was created by Alfredo Martinez

1.IDENTIFYING CHARACTERISTICS

Unicellular true fungi
Facultative anaerobe
Cells typically between 5-10um in diameter
Cells appear oval or spherical in shape
Reproduce by budding
1-4 spherical or short oval spores
Cell wall composed of B-1,3 and B-1,6 glucan and
mannan
True mycelium never present
The universal model eukaryote

The arrows in the image (left) show Saccharomyces cerevisiae replication by "budding"

2. TAXONOMIC DESCRIPTION

Saccharomyces is the universal model of a eukaryote cell and the best understood. The 16 chromosomes of Saccharomyces cerevisiae were sequenced in April 1996. The Yeast Genome Directory was published in June 1997, and is used by molecular biologists worldwide.

Saccharomyces is known as “budding yeast” due to the fact replication occurs by multilateral budding. The vegetative cell can either be haploid or diploid. In diploid species spores are produced directly in the vegetative cells, while in haploid species conjugation between two vegetative cells immediately precedes ascus formation. Between one and four spherical spores, form in each ascus. All species have respiratory as well as a fermentation metabolism.

Saccharomyces cerevisiae is known as the “Baker’s” or “Brewer’s” yeast. These organisms have long been utilized to ferment the sugars of rice, wheat, barley, and corn to produce alcoholic beverages and in the baking industry to expand, or raise, dough. This fermentation gives off carbon dioxide and ethanol. The carbon dioxide is trapped within tiny bubbles and results in the dough expanding, or rising.

The cell wall of Saccharomyces is said to have “yeast cellulose.” This is due to its composition of B-1,3 glucan and B-1,6 glucan linkages. Most higher plant cellulose have B-1,4 glucan linkages. Only about 30-35% of the cell wall is composed on glucan. Another 30% is mannan, a water-soluble polysaccharide of the sugar D-mannose. The remaining percent is composed of 1-2% chitin, 10% lipids and a small percent of inorganic molecules.

*The above image shows Saccharomyce cerevisiae with ascus and four spores in the middle of the cell

3. ISOLATION AND ECOLOGY

Saccharomyces is easily grown on a variety of different laboratory media. One of the oldest media used to cultivate Saccharomyces is malt extract or beer wort. The basic component need for growth includes a carbon source, usually glucose, a nitrogen source, usually ammonium sulfate, vitamins and minerals. Saccharomyces has an optimum temperature range of 20-25? Celsius. They are able to survive a wide range of temperatures ranging from 0-40 Celsius.

Saccharomyces is found in many natural locations, and in animals, and insects. Saccharomyces can be found in plant leaves, that excrete a sugary fluid, and Saccharomyces use these as a carbon source. Another location Saccharomyces can grow on plants in on trees. Saccharomyces use the sugary sap excreted by injured trees as the carbon source for growth. Saccharomyces is also found in the intestines of some warm-blooded animals and is very common in wild Drosophila species.

The above images shows Saccharomyces grown on SDA agar in a petri dish.

4. ADDITIONAL SOURCES OF INFORMATION

Phaff, H. J., Miller, M.W., and Mrak, E.M. 1968. The Life of Yeast. Harvard University Press. Cambridge, Mass. 23-30, 83-123 pp.

Dickinson, J. R., Schweizer, M. 1999. The Metabolism and Molecular Physiology of Saccharomyces cerevisiae. Philadelphia, PA. 1-44 pp.

Cook, A.H. 1958. The Chemistry and Biology of Yeasts. New York, New York. 63:251 pp.

5. LINKS TO OTHER SITES ON Saccharomyces

http://genome-www.stanford.edu/Saccharomyces/VL-what_are_yeast.html

Http://sequence-www.stanford.edu/