Enhanced Heat Tolerance and Optimization of Activity Temperature in Aspergillus niger NRRL 3135 Phytase (PhyA) by Elimination of a Disulfide Bridge

Boone S. A., Mullaney E.

Author address: 

ARS-USDA, New Orleans, LA.


The utilization of microbial phytases in animal feed, rich in phytate, and intended for animals with simple stomachs is now widely accepted. The commercial phytases currently available are all histidine acid phosphatases (HAP) and have been termed histidine acid phytases (HAPhy). The HAPhy enables swine, poultry, and other monogastric animals to hydrolyze phytate and thus utilizes the phytin phosphorus for nutrition and also lowers the phosphate level of manure. The optimum temperature for the wild type HAPhys is substantially higher than the body temperature of all these animals and thus the activity of the enzyme is not at its optimum. Only 21.3% of the activity is retained when the enzyme is subjected to elevated temperatures for a brief period, which is necessary for the processing of the animal feed. In this study the optimum temperature was lowered while the residual phytase activity after heating to 70oC was raised in a widely utilized phytase, Aspergillus niger NRRL 3135 PhyA. This was accomplished by site-directed mutagenesis of the cysteines that are involved in the formation of a single disulfide bridge (DB). When compared to wild type (WT), three of the four mutant phytases displayed a lower optimum temperature, 42oC, and up to a four-fold increase in activity after heating. These findings have a potentially broad application to be incorporated along with other desirable features to engineer a phytase with superior attributes for animal feed applications.

abstract No: 


Full conference title: 

110th General Meeting American Society for Microbiology
    • ASM 110th (2010)