Cellulose Degradation by Ruminal Microorganisms

Abstract

The rumen i s a highly developed digestive organ in which feed material, particularly plant fiber, is efficiently digested by a complex microbial fermentation. Cellulose, the major component of plant fiber, is digested in the rumen by an assemblage of anaerobic bacteria, fungi, and protozoa. While pure cellulose itself is completely digestible under the proper environmental conditions, the matrix interactions among structural biopolymers in natural plant material prevent the complete digestion of the cellulose component. Ruminal bacterial are probably the most active cellulose degraders in the rumen, but the fungi also play an important role, particularly in the physical disruption of recalcitrant tissue to render the cellulose more accessible to degradative enzymes. Cellulose degradation in the rumen is enhanced by attachment of microbial cells to the substrate and by synergistic interactions with noncellulolytic microbes, but is inhibited by factors that produce a low ruminal pH. Recent advances in continuous culture techniques and in the molecular biology of cellulase enzymes have permitted a better understanding of the cellulolytic process. Enhancement of ruminal cellulose fermentation will be best achieved in the near term by exploitation of recent improvements in the technology of substrate pretreatment. However, advances in the development of improved rumen microbial strains and more digestible forage varieties may yield additional improvements in ruminant cellulose utilization.

Physiological variability in volatile organic compounds (VOCs) in exhaled breath and released from faeces due to nutrition and somatic growth in a standardized caprine animal model

“…Becoming ruminants, cellulose and other complex carbohydrates are degraded by the gastrointestinal microbiota into volatile fatty acids (VFAs, e.g. acetate, propionate and butyrate) that replace glucose as the primary source of energy (Weimer 1992, Van Soest 1994. The decrease in plasma glucose in the first few weeks correlates with the increasing concentration of VFAs in blood (McCarthy and Kesler 1956).…”

In vitro methane formation and carbohydrate fermentation by rumen microbes as influenced by selected rumen ciliate species

“…Both crystalline and amorphous cellulose are occurring in forages (Weimer 1992). The other carbohydrate type used was xylan (a form of highly complex polysaccharides; produced from oat spelts; product number 38500 (discontinued product; Serva, Heidelberg, Germany), serving as a model for hemicellulose.…”

Predicting the profile of nutrients available for absorption: from nutrient requirement to animal response and environmental impact

“…The engulfment of solid feed particles by protozoa is well known and this is also expected to result in engulfment of bacteria attached to these particles. On the other hand, the converse hypothesis of protection against engulfment by means of attachment, has been supported by observations that the fluid-phase, non-fibrolytic bacteria increase to a far higher extent upon defaunation than do the attached bacteria (Weimer, 1992). However, it should be noted that the preference of protozoa for starch and sugars, rather than fibre, will result in a relatively higher availability of starch and sugars compared to fibre upon defaunation and hence a smaller increase in attached, fibrolytic bacteria compared to non-attached bacteria.…”