Development of a general defined medium for Pichia pastoris

Pichia pastoris is widely used as a host for recombinant protein production. More than 500 proteins have been expressed in the organism at a variety of cultivation scales, from small shake flasks to large bioreactors. Large-scale fermentation strategies typically employ chemically defined growth medium because of its greater batch-to-batch consistency and in many cases, lower costs compared to complex medium. For biopharmaceuticals, defined growth medium may also simplify downstream purification and regulatory documentation. Standard formulations of defined media for P. pastoris are minimal ones that lack the metabolic intermediates provided by complex components such as peptone and yeast extract. As a result, growth rates and per-cell productivities are significantly lower than in complex medium. We have designed a rich defined medium (RDM) for Pichia pastoris by systematically evaluating nutrients of increasing complexity and identifying those that are most critical for growth. We have also employed transcriptomics to gain deeper insights into the underlying metabolic processes and inform our media design. We have demonstrated that using RDM for expression of three heterologous proteins yields titers comparable to, or higher than, those in standard complex medium. RDM improves productivity of P. pastoris fermentations and its development demonstrates the usefulness of transcriptomics to accelerate process development for new molecules.