Plant structural polysaccharides provide a major source of nutrient for ruminant livestock. These carbohydrates are not degraded by mammalian-derived enzymes, but are hydrolysed by rumen microbial plant cell wall hydrolases. In view of the pivotal role of microbial cellulases and xylanases in ruminant nutrition, there has been considerable interest in these enzymes. In this paper we wish to illustrate how recombinant DNA (rDNA) technology can be utilised to dissect the biochemistry and molecular architecture of these enzymes, and provides us with the opportunity of generating novel cellulases and xylanases with increased capacity to hydrolyse the plant cell wall.

In general cellulases and xylanases from anaerobic microbes associate into large molecular weight complexes, whose integral structures are responsible for the efficient hydrolysis of plant structural polysaccharides. The feasibility of altering these complexes, or transferring them to other organisms represents a significant challenge.