Purification and characterization of an acidic, thermophilic phytase from a newly isolated Geobacillus stearothermophilus strain DM12

Microbial phytases were applied mainly to animal and human foodstuffs in order to improve mineral bioavailability and food processing. In addition, phytases have potential biotechnological application in various other fields, such as environmental protection, aquaculture and agriculture. Bacillus sp. DM12, an isolate from a hot spring, produces phytase, which catalyzes the hydrolysis of phytic acid into myo-inositol and inorganic phosphates. Phytase from Bacillus sp. DM12 was purified using ammonium sulfate precipitation and dialysis, followed by anion exchange and gel filtration chromatography. Molecular weight of the purified phytase was estimated to be 28 kDa by SDS-PAGE. Km and Vmax values for sodium phytate were 0.177 mM and 1.126 μmol/min, respectively. The optimum temperature for phytase activity was found to be 50°C. The enzyme retained over 75% of its activity over a temperature range of 30 to 80°C. The highest phytase activity was observed at pH 4.5 and a decline of enzyme activity was observed on both sides of pH optimum. The enzyme was stable over the pH range of 3.0 to 6.0. The enzyme retained over 80% of its activity in the presence of 5 mM metal ions except CaCl2. It is also indicated that the enzyme retained over 65% of its activity over a 5 mM metal ions. These properties suggest that this phytase is a suitable enzyme for the hydrolysis of phytic acid and phytates in food and feed processing industries.