Yeast

Yeast

The leader in libations, the king of the kitchen, this tiny organism rises to the top when it comes to making delicious food. Of course, I'm talking about the fomenter of fermentation, Saccharomyces cerevisiae, more commonly known as yeast.









Scanning electron microscope images of yeast cells (source: Chemistryland.com). Yeast cells divide by a process called budding, present on these cells as small round dots.


Under low oxygen conditions, Saccharomyces, or "sugar fungus", can perform a very special form of metabolism called ethanol fermentation. The production of CO2 gas causes bread to rise and gives beer and champagne its fizz. And the ethanol? Well, you know. But, of course, the yeast really care about the energy produced by fermentation that sustains growth and reproduction. I'll note here that yeast grows a lot more efficiently using aerobic respiratory metabolism (like us humans) than anaerobic fermentation.

























Making beer is fun! At the Microbial Diversity course in Woods Hole, MA, students learn first-hand about yeast fermentation.


Yeast in the Environment

In the family tree of life, S. cerevisiae belongs to the domain Eukarya (meaning it's more closely related to humans than to bacteria), and the phylum Fungi. While we generally refer to S. cerevisiae as 'yeast', there are many species that belong to this broader yeast group. Some species have real benefits to us (like baker's yeast), while we don't know very much about many (like most organisms...), and others cause illness (e.g. Candida species). In the environment, fungi play an important role in cycling nutrients by decomposing organic matter so that nutrients become available for plants and micro-organisms. They are the "filters" of the environment, so it's no surprise that they do a great job cleaning up polluted land. S. cerevisiae and other yeasts are known to remediate Chromium (1), a poisonous metal that was made famous in the Julia Roberts film "Erin Brockovich".

Yeast is a relatively simple eukaryotic organism, being single-celled and easy to grow in a laboratory setting. For these reasons, it has become a model organism for scientific research. We have learned a lot about ourselves through understanding the biology of yeast cells. Some truly revolutionary analytical tools were developed using yeast, such as the two-hybrid assay (2), which has revealed insights into cancer biology (3), endocrine disruptors (4), and cell signaling (5), among much more.

We all can appreciate a tiny organism that can make delicious tasting food and beverages. But now that we know that there is so much more to this important microbe, we should all bow down to the king of the kitchen.


References
1. Ksheminska et al., Process Biochemistry, 2005: 1565-1572.
2. Interested? Check out Wikipedia for more information!
3. Li and Fields, FASEB Journal, 1993: 957-963.
4. Nishihara et al., Journal of Health Science, 2000: 282-298.
5. Staudinger et al., Journal of Cell Biology, 1995: 263-271.