Transgenic mice expressing bacterial phytase as a model for phosphorus pollution control

We have developed transgenic mouse models to determine whether endogenous e xpression of phytase transgenes in the digestive tract of monogastric anima ls can increase the bioavailability of dietary phytate, a major but indiges tible form of dietary phosphorus. We constructed phytase transgenes compose d of the appA phytase gene from Escherichia coli regulated for expression i n salivary glands by the rat R15 proline-rich protein promoter or by the mo use parotid secretory protein promoter. Transgenic phytase is highly expres sed in the parotid salivary glands and secreted in saliva as an enzymatical ly active 55 kDa glycosylated protein. Expression of salivary phytase reduc es fecal phosphorus by 11%. These results suggest that the introduction of salivary phytase transgenes into monogastric farm animals offers a promisin g biological approach to relieving the requirement for dietary phosphate su pplements and to reducing phosphorus pollution from animal agriculture.