Production and purification of a novel thermostable phytase by Pichia pastoris FPHY34

A genetically engineered Pichia pastoris FPHY34 strain containing a 1.3 kb thermostable phytase gene (fphy) evolved by DNA shuffling was constructed and screened. Expression and purification conditions for the recombinant phytase were developed in this study. The effect of Pi on recombinant phytase expression and cell growth of P. pastoris FPHY34 was tested in shake flask culture. Optimization of carbon sources for cell growth and methanol feeding strategies for phytase expression in P. pastoris FPHY34 was carried out in a 50-L fermenter by fed-batch fermentation. The purification of phytase was investigated by micro-filtration and ultra-filtration followed by desalting, ion-exchange chromatography, and gel filtration in the ÄKTA system. It showed that the optimum inorganic phosphorus is 13.6 g L−1 and that glucose can be used as a substrate for P. pastoris cell growth instead of glycerol; the biomass yield of glycerol (YX/S) is slightly higher than that of glucose. Different profiles of lag phase and respiratory quotient (RQ) displayed between glucose and glycerol as the sole carbon source. The maximum phytase activity in per millimetre reached 2508 U mL−1 at a methanol feed rate of 3.0 mL L−1 h−1 after 80 h period of induction. A purification factor of 41.1 with a 32% yield was achieved after chromatographic purification. The specific enzyme activity was 80 U mg−1 and 3281 U mg−1 in that supernatant fraction and after gel filtration purification, respectively. The strain P. pastoris FPHY34 showed a promising application in phytase industrial production.