Aims: Using gene cloning and overexpression to obtain a potential industrial phytase as a feed additive to upgrade the nutritional quality of phytate-rich seed-based animal feed.
Methods and results: A phyA gene from a high extracellular phytase-producing Aspergillus niger sp. was cloned and overexpressed in Pichia pastoris GS115 using the secretive expression vector pPICZalphaA. After cultivation for 4 days in buffered methanol complex medium (BMMY) containing methanol for induction, catalytically active phytase was secreted as a predominantly extracellular protein. The activity of the expressed phytase in fermented broth was 30 000-fold higher than that of native phytase with a specific activity of 503 U mg(-1). The Lineweaver-Burk plot indicated K(m) values of 0.196 mmol l(-1) for sodium phytate and 18.16 mmol l(-1) for p-nitrophenylphosphate (pNPP). Thermostability studies showed that recombinant phytase retained 70% activity after exposure to 90 degrees C for 5 min and 65% activity after 30 min, much higher than for commercial phytase.
Conclusions: The higher activity and high thermostability of recombinant phytase enable it to withstand the temperatures of the feed pelleting process.
Significance and impact of the study: The characteristics of this recombinant phytase, especially the good thermostability, are likely to render it of potential industrial importance.