Targeted expression of microbial cellulases in transgenic animals

In non-ruminant livestock the use of plant structural carbohydrates, such as cellulose and xylan, as a dietary source is limited by the lack of intestinal enzymes to degrade this material to simple sugars. Any dietary energy made available is through the action of microbes in the hind gut, but this fermentation is inefficient with the production of volatile fatty acids rather than simple sugars. The nutrition of such simple-stomached animals could, therefore, be significantly improved by the introduction of plant degrading enzymes such as cellulases and xylanases into their gastrointestinal (GI) tract. We have expressed a bacterial gene from Clostridium thermocellum encoding a cellulase endoglucanase E′, in the exocrine pancreas of a simple-stomached animal model, the mouse. A catalytically active enzyme is synthesized and secreted into the small intestine which is resistant to proteolytic inactivation. Currently the level of expression is low so we are attempting to maximise expression by gene rescue experiments. In addition we are also attempting to express this gene in the intestinal enterocytes, lining the GI tract, using a glycosylphosphatidylinositol sorting signal to direct the secretion of the bacterial protein into the intestinal lumen.