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H Tan, J Tang, X Li, T Liu, R Miao, Z Huang, Y Wang, B Gan and W Peng
Psychrophilic phytases suitable for aquaculture are rare. In this study, a phytase of histidine acidic phosphatase (HAP) family was identified in Morchella importuna, a psychrophilic mushroom. The phytase showed 38% identity with Aspergillus niger PhyB, which was the closest hit. The M. importuna phytase was overexpressed in Pichia pastoris, purified and characterized. The phytase had an optimum temperature at 25°C, which is the lowest among all the known phytases to our knowledge. The optimum pH (6.5) is higher than most of the known HAP phytases, which is fit for the weak acidic condition in fish gut. At the optimum pH and temperature, MiPhyA showed the maximum activity level (2384.6±90.4 μmol/min/mg), suggesting that the enzyme possesses a higher activity level over many known phytases at low temperatures. The phytate degrading efficacy was tested on three common feed materials (soybean meal/rapeseed meal/corn meal) and was compared with the well-known phytases of Escherichia coli and Aspergillus niger. When using the same amount of activity units, MiPhyA could yield at least 3× inorganic phosphate than the two reference phytases. When using the same weight of protein, MiPhyA could yield at least 5× inorganic phosphate than the other two. Since it could degrade phytate in feed materials efficiently under low temperature and weak acidic conditions, which is common for aquacultural application, MiPhyA might be a promising candidate as a feed additive enzyme.
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Oxygen, Phosphoric acid, Metabolism, Uranium, Enzyme, Escherichia coli, PH, Protein
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