Life Cycle of Saccharomyces cerevisiae

One of the major characteristic of the yeast cycle is that its life form can be very well controlled by manufacture, to elaborate from last blog. Saccharomyces cerevisiae exists in haploids two mating types, a-factor and alpha factor with each having chromosome. As haploid they can maintain haploids still, and divide to form a colonies of haploid cells using mitosis. However, a-factor and alpha-factor parents can mate and reproduce a diploid cell that contains two chromosomes which means it includes both the a-factor and alpha-factor genetic strains. This diploid cell is stable and is capable of growing independently using mitosis like its haploid parents. Yeast can also undergoes meiosis to create gametes called spores. The same diploid cells after meiosis and produces four spores stored in an ascus. The chromosomes as a result of meiosis and crossing over will be 2 recombinant chromosomes, and one of each parental chromosomes.

In its mitotic cell cycle, Saccharomyces cerevisiae uses a process called budding to reproduce. Budding can stop budding if the environment either lacks nutrients or a possible mate is close by. If under harsh environment, proliferation of the yeast cell would cease, and if a mate is available near by sexual production would occur.  Saccharomyces cerevisiae is a heterotroph that eats sucrose, maltose, fructose and glucose. Specifically for healthy fermentation for wine production, fructose and glucose from grapes would be the main source for energy, under anoxic conditions of course.

Saccharomyces cerevisiae

A single cell of Saccharomyces cerevisiae has a diameter of 7.94 μm, and its size varies widely depending where it is at during the process of budding. S.cerevisiae can exist as a unicellular organism or a pseudo-hyphae. As a unicellular organism it exists as the yeast form, and as pseudohyphae form under nitrogen starvation ( Blaketer 1993). Unlike other fungi, it is not capable of forming a fruiting body. The cell wall of Saccharomyces have ester-linked lipids and a large chitin content. Its cell wall is very thick and layered which comes with many advantages when it comes to its stability and resistant in acidic environment. Its haploid form is the form used in the production of food, to inhibit reproduction thus have a tight control over population number within the food product. 

The genome of S. cerevisiae is one of the first species to be sequenced completely with 5885 different protein encoding genes as long as 12068 kilo bases ( Goffeau 1996). 

The Chateau Elan Winery

I cannot imagine a more delectable way to learn about microbiology than a visit to The Chateau Elan Winery. This winery is in the heart of Braselton, Georgia just less than an hour away from the metropolitan Atlanta. The winery is also a resort. Upon arrival there is a beautiful mansion surrounded by fields of greenery that alludes to the mansion and garden of Versailles. I opted for the standard public tour which features tours of the vineyards, tasting room and production facility. We started with enjoying a glass of white wine in the tasting room.

Then, we moved on the field. With a closer look of the field, I notice that the climate was quite hot and dry. The plants did not seem to be in striving conditions. The reason being that stressful environment makes a more aromatic and flavorful grapes due to the stress hormones released. We further get to look at the importance of the composition and physical characteristics of soil that would make great grapes.

Lastly, we get to the production facility containing thousands of wine barrels. Here, the wine attendant briefly goes over the most important process where sugars from the grape juice is converted to wine. This important role is carried out by the yeast that was inoculated into the tanks. Tanks storing the grapes must be in a anoxic condition for fermentation to occur. A popular yeast strain used to convert glucose into ethanol is the Saccharomyces. At the site, the microbe is invisible of course, but I could definitely smell them. As a wine enthusiast and a self proclaimed sommelier, the role of this microbe in the winemaking definitely called out to me.