[Improving thermostability of Aspergillus niger phytase by elongation mutation].

The phytase gene phyA(m) from Aspergillus niger N25 was recombined into E. coli expression vector pET-30b(+). Recombined at expression vectors pET30b-FphyA(m) was served as a template to amplify phytase gene, and the PCR product named elongation mutation gene phyA(e) was expanded with a 13 amino acid sequence from pET-30b-FphyA(m) vector at C-terminal of phytase gene phyA(m). Furthermore, phyA(e) gene was recombined into expression vector pPIC9k and expressed in Pichia pastoris. The comparison experiment of mutant phytase PP-NP0 with wild-type phytase PP-NP(m)-8 showed that: the optimum temperature of PP-NPe was increased by 3 degrees C, and its thermostability was increased by 21% when it was exposed to 10 min at 75 degrees C. Its effective reaction pH range with catalysis efficiency above 70% was pH 4.6 - pH 6.6, and wider 0.4 pH value than that of wild-type phytase.