Bioprocess engineering aspects of heterologous protein production in Pichia pastoris: A review

Pichia pastoris is currently one of the most effective and versatile systems for the expression of heterologous proteins. Its success is due to its powerful methanol-inducible alcohol oxidase 1 (AOX1) promoter, capacity to perform post-translational modifications and pathways leading to recombinant products secretion. Despite its advantages, P. pastoris cultivation is plagued by high protease expression levels, high sensitivity to methanol levels, nutrient-deficiency when grown on defined media, difficulties in systematic study due to product-specific effects, and health and safety concerns associated with the storage of large quantities of methanol. Difficulties also arise that are specific to the cultivation methods and control strategies used.The present review discusses several bioprocess engineering aspects related to P. pastoris cultivation, including the different promoters available, both constitutive and inductive, on- and off-line process parameter monitoring methods, fed-batch and continuous cultivation control strategies, proteolytic degradation of products and methods to minimize associated yield reductions, and the different models devised to describe cell growth and protein production. The economics of P. pastoris cultivation, through a case-study involving recombinant phytase production, are also discussed. The study of yeast fermentation is currently very dynamic, and P. pastoris is on its way towards becoming a standard expression system.