Abstract

Phytase is a new-style enzyme used in animal feed additive. It can increase phosphorus availability, decrease environmental phosphorus pollution and improve the performance of animals. Phytase gene was cloned by reverse transcription-polymerase chain reaction (RT-PCR) using first strand cDNA as template after reverse transcripting Aspergillus niger total RNA. The phyA gene was cloned into plasmid pYD1 which allows regulated expression, secretion and detection of expressed proteins on the surface of Saccharomyces cerevisiaecells using immunofluorescence. The construct was propagated in Escherichia coli DH5α and then was transformed into the yeast strain EBY100. After induction, the phytase activity was measured every 12 h. The results indicated that the activity of the fusion protein reached the highest level after being induced with 2.0% galactose for 48 h. This enzyme had pH optima (pH 7) and its optimum temperature was about 65°C.

Key words: Yeast surface display, Aspergillus niger, phytase.