Characterisation of bacterial multiple inositol polyphosphate phosphatases relevant to the animal feed industry

Phytases are enzymes that degrade phytate, the main storage form of phosphorus in plants. Animal feed industries use plant-based feed with abundant phytate content. Without the supplementation with phytases, the animals would not be able to access the phosphorus in the form of phosphate stored in the phytate molecule. This thesis describes research carried out to characterise a group of bacterial phytases from Bacteroides thetaiotaomicron, Bifidobacterium infantis and Bifidobacterium pseudocatenulatum with comparisons to an existing commercial phytase, Quantum Blue. The enzymatic properties, product profiles, binding and thermostability were examined and the structure of the binding site at various stages of the catalytic cycle was investigated with the aid of active site mutagenesis. X-ray structure of the active site mutant helped elucidate the structure of the intermediate and product-bound forms of the Bifidobacterium infantis phytase. Further mutagenesis experiments examined the function of disulphide bridges in the enzyme. The experimental results described in this work provide novel insights into the hydrolysis of phytate by bacterial phytases, the conformational changes during the catalytic cycle and the contribution of disulphide links to thermostability of the enzyme. These results lay the foundations of the work toward optimisation of phytases for use by the industry of the animal feed supplements