Yeast Fermentation

What is yeast fermentation? When thinking of yeast fermentation in bioprocessing, food, ethanol and biofuel production may come to mind. However, yeast is a versatile microorganism that is also widely used in the biopharmaceutical industry, for the expression of recombinant proteins to prevent or treat diseases. Industry-relevant yeast species include Saccharomyces cerevisiae and Pichia pastoris.
Yeast fermentation is well suited for the large-scale production of therapeutic proteins, due to:

• Fast growth rate
• Easy genetic manipulation
• High cell productivity
• Ability to be grown at high cell densities
• High tolerance to deviations in pH and temperature (compared to mammalian cells)
• Cheaper costs and shorter cultivation cycles than mammalian cell cultures

Microorganisms including and yeast are ideal for large-scale bioprocessing due to their high yields and fast growth. However, an advantage of yeast cells in particular is that they are eukaryotic and so they are more comparable to human cells. Consequently, yeast cells can perform a range of post-translational protein modifications that bacteria are unable to. These modifications are essential for the functioning of therapeutic proteins and include glycosylation, protein folding and phosphorylation.

Pichia pastoris is a popular species for yeast fermentation in the large-scale production of recombinant proteins. This yeast species is capable of achieving high cell densities and protein yields, and is also easy to scale up, demonstrating high levels of reproducibility in small-scale, through to bench-scale and production-scale bioprocesses. In shakers or bioreactors of any size, Pichia pastoris can be used as a powerful protein expression system.

Developing a commercially viable yeast fermentation process requires the optimization product yields. An adequate supply of nutrients must be ensured, to support high cell densities. The promoter system is another important factor that determines protein expression. Here we will have a look at some factors that can contribute to the optimization of protein expression in yeast.