Submitted to: Journal of Dairy Science
Publication Type: Proceedings
Publication Acceptance Date: June 28, 1995
Publication Date: N/A
Technical Abstract: The bacteria Fibrobacter succinogenes, Ruminococcus flavefaciens, and R. albus are generally regarded as the predominant cellulolytic microbes in the rumen. These bacteria are the most actively cellulolytic of all mesophilic organisms described to date from any habitat. As a group, these species are extremely specialized nutritionally. Moreover, each species has apparently evolved to similar maximum rates of cellulose digestion. Active cellulose digestion involves adherence of cells to the fibers via a glycoprotein glycocalyx that both protects cells from protozoal grazing and the cellulolytic enzymes from degradation by ruminal proteases, and retains --at least temporarily--the cellodextrin products for use by the cellulolytic bacteria. These properties result in different lifestyles for the adherent and nonadherent populations of each species, but overall provide enormous selective advantage in the rumen environment. However, major constraints to cellulose digestion are provided by plant cell wall structure (matrix interactions among wall biopolymers and low substrate surface area) and by limited penetration of the nonmotile cellulolytic microbes into the plant cell lumen. Because of these constraints and the highly adapted nature of cellulose digestion by the predominant ruminal cellulolytic bacteria, transfer of cellulolytic capabilities to non- cellulolytic ruminal bacteria (e.g., by genetic engineering) that display other desirable properties offers limited opportunities to improve ruminal cellulose digestion.