Molecular and Biochemical Characteristics of Recombinant β-Propeller Phytase from Bacillus licheniformis Strain PB-13 with Potential Application in Aquafeed

Phytic acid is the major storage form of organic phosphorus in nature- and plant-based animal feed. It forms insoluble complexes with nutritionally important metals and proteins that are unavailable for monogastric or agastric animals. Phytases initiate the stepwise hydrolysis of phytic acid and release inorganic orthophosphate. In the present investigation, the phytase gene from a phytase producing Bacillus licheniformis strain PB-13 was successfully expressed in Escherichia coli BL21. Recombinant phytase 'rPhyPB13' was found to be catalytically active, with an activity of 0.97 U/mL and specific activity of 0.77 U/mg. The rPhyPB13 was purified to 14.10-fold using affinity chromatography. Similar to other beta-propeller phytases, purified rPhyPB13 exhibited maximal activity at pH 6.0-6.5 and 60 A degrees C in the presence of 1 mM Ca2+ and was highly active over a wider pH range (pH 4.0-8.0) and high temperature (80 A degrees C). It has shown maximum activity towards Na-phytate as substrate. The observed K (m) , V (max) and k (cat) of purified rPhyPB13 were 1.064 mM, 1.32 mu mol/min/mg and 27.46 s(-1), respectively. PhyPB13 was resistant to trypsin inactivation, activated in presence of Ca2+ and inhibited in presence of EDTA. Crude rPhyPB13 has good digestion efficiency for commercial feed and soybean meal. These results indicate that PhyPB13 is a beta-propeller phytase that has application potential in aquaculture feed.