The cloning and expression of a native gene encoding a Bacillus subtilis phytase using Pichia pastoris as the host is described. In addition, the influence of N-glycosylation on the biochemical properties of the B. subtilis phytase, the influence of pH on the thermostability of the recombinant and native B. subtilis phytases, and the resistance of both phytases to shrimp digestive enzymes and porcine trypsin are also described. After 48 h of methanol induction in shake flasks, a selected recombinant strain produced and secreted 0.82 U/ml (71 mg/liter) recombinant phytase. This phytase was N-glycosylated, had a molecular mass of 39 kDa after N-deglycosylation, exhibited activity within a pH range of 2.5 to 9 and at temperatures of 25 to 70°C, had high residual activity (85% ؎ 2%) after 10 min of heat treatment at 80°C and pH 5.5 in the presence of 5 mM CaCl 2 , and was resistant to shrimp digestive enzymes and porcine trypsin. Although the recombinant Bacillus phytase had pH and temperature activity profiles that were similar to those of the corresponding nonglycosylated native phytase, the thermal stabilities of the recombinant and native phytases were different, although both were calcium concentration and pH dependent.

Thermostable phytases, which are active over broad pH ranges, may be useful as feed additives, since they can resist the temperatures used in the feed-pelleting process. We designed new beta-propeller phytases, using a structure-guided consensus approach, from a set of amino acid sequences from Bacillus phytases and engineered Pichia pastoris strains to overproduce the enzymes. The recombinant phytases were N-glycosylated, had the correct amino-terminal sequence, showed activity over a pH range of 2.5 to 9, showed a high residual activity after 10 min of heat treatment at 80°C and pH 5.5 or 7.5, and were more thermostable at pH 7.5 than a recombinant form of phytase C from Bacillus subtilis (GenBank accession no. AAC31775). A structural analysis suggested that the higher thermostability may be due to a larger number of hydrogen bonds and to the presence of P257 in a surface loop. In addition, D336 likely plays an important role in the thermostability of the phytases at pH 7.5. The recombinant phytases showed higher thermostability at pH 5.5 than at pH 7.5. This difference was likely due to a different protein total charge at pH 5.5 from that at pH 7.5. The recombinant beta-propeller phytases described here may have potential as feed additives and in the pretreatment of vegetable flours used as ingredients in animal diets.

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