Yeast is a unicellular eukaryotic microorganism belonging to the fungal kingdom, widely used as a host cell system in biopharmaceutical manufacturing due to its ability to combine the rapid growth, genetic tractability, and cost-efficiency of microbial systems with the eukaryotic post-translational modification capabilities — including glycosylation, disulfide bond formation, and protein folding — required for the production of complex recombinant proteins. The most commonly used yeast species in bioproduction include Saccharomyces cerevisiae — recognized as a Generally Recognized As Safe (GRAS) organism and used for the manufacture of vaccines, insulin, and growth hormones — and Pichia pastoris (reclassified as Komagataella phaffii), favored for its high-yield secretory expression system and suitability for fed-batch fermentation at industrial scale. Yeast-based expression systems are a core manufacturing platform offered by CDMOs for the production of biologics, enzymes, antibody fragments, and plasmid DNA (pDNA).
