A mini-scale mass production and separation system for secretory heterologous proteins by perfusion culture of recombinant Pichia pastoris using a shaken ceramic membrane flask

Abstract

The perfusion culture technique using a shaken ceramic membrane flask (SCM flask) was applied to the production of a secretory heterologous protein. A recombinant methylotrophic yeast strain, Pichia pastoris, was cultured aerobically on a reciprocal shaker using an SCM flask. High-level production of human serum albumin (HSA) was attempted by increasing both the cell concentration and the expression level of the recombinant gene. In the two-stage culture method, the cell concentration was first raised to 17 g/ l by feeding glycerol, after which the expression of HSA was induced by feeding methanol. However, the concentration of HSA in the effluent filtrate was as low as 0.15 g/ l, while the cell concentration continued to increase. In contrast, HSA was effectively produced by feeding methanol from an early stage of the culture. In this case, the HSA concentration reached 0.24 and 0.46 g/ l, respectively, using the growth-associated production method without and with aeration into the head space of the SCM flask. The results showed that supplying sufficient oxygen together with the growth-associated induction method are effective for obtaining high-level expression of the methanol-inducible recombinant gene of P. pastoris. An HSA concentration in the filtrate of 1.5 g/ l was finally achieved when the cell concentration was increased to 53 g/ l by supplying oxygen-enriched gas to the SCM flask. The yield and productivity of HSA reached 2.6-fold and 10-fold those obtained in an ordinary fed-batch culture using a shake flask, and these levels were readily achieved by continuous replenishment of the culture supernatant. The achievements made in this study should contribute to the development of a handy bioreactor system for mini-scale mass production of target proteins with separation at high purity.