Using Pichia pastoris to produce recombinant glycerol kinase
The methylotrophic yeast Pichia pastoris has been developed into an efficient expression system for the production of recombinant protein under the tight control of the methanol-induced alcohol oxidase promoter (pAOX1). In this study, a 2.5-liter culture system was developed for the growth of a P. pastoris strain bearing the GUT1 gene from Saccharomyces cerevisiae for the expression of recombinant glycerol kinase (GK). The best culture conditions to produce high levels of secreted GK were investigated by growing the recombinant strain of P. pastoris in shake flasks and a fermenter. Cell growth and enzyme production were found to be optimal after two days of growth. Enzyme production was affected by the nitrogen source, Difco peptone being the most appropriate for this purpose. Three different rates of air flow (1 to 3 L/min) were tested to observe their effect on cell growth and the secretion of GK into a medium containing 1% methanol as the sole carbon source. Increasing the rate of air bubbling in the culture medium enhanced both cell growth and GK activity, reaching a dry biomass of 7.84 mg/mL, cell viability of 98.4% and a maximal GK activity of 1.57 U/ mL, at a flow rate of 2.0 L/minute, at 30° C and pH 6.0. Moreover, the enzyme activity in the P. pastoris culture medium was 2.3 times higher under these conditions than in the shake-flask culture, demonstrating the significant influence of aeration on biomass production and GK activity secreted by P. pastoris.