In order to study on the relationship between Escherichia coli AppA phytase's thermostability and salt bridges, and indicate an effective technical route of which factor to think about and where to modify at AppA for enhancing its thermostability, a salt bridge subtraction mutant E31Q and a salt bridge addition mutant Q307D were constructed by site-directed mutagenesis. The residual activities of the wild-type AppA phytase, E31Q and Q307D were 31.42%, 17.46%, and 40.57%, respectively, after being heated at 80 degrees C for 10 min. The salt bridge subtraction mutant E31Q showed 13.96% thermostability decreasement, and the salt bridge addition mutant Q307D showed 9.15% thermostability enhancement than the wild-type both without the pH and temperature optimum changed. It proved salt bridges play a key role in E. con AppA phytase's thermostability and the alpha/beta-domain of AppA may be sensitive to heat. Salt bridges and the alpha/beta-domain of AppA should have high priority to think about to enhance AppA's thermostability for commercial application. Besides, molecular dynamics simulation was used for salt bridges analysis. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.