Quantitative analysis of cellulose degradation and growth of cellulolytic bacteria in the rumen

Abstract

Ruminant animals digest cellulose via a symbiotic relationship with ruminal microorganisms. Because feedstuffs only remain in the rumen for a short time, the rate of cellulose digestion must be very rapid. This speed is facilitated by rumination, a process that returns food to the mouth to be rechewed. By decreasing particle size, the cellulose surface area can be increased by up to 10(6)-fold. The amount of cellulose digested is then a function of two competing rates, namely the digestion rate (K(d)) and the rate of passage of solids from the rumen (K(p)). Estimation of bacterial growth on cellulose is complicated by several factors: (1) energy must be expended for maintenance and growth of the cells, (2) only adherent cells are capable of degrading cellulose and (3) adherent cells can provide nonadherent cells with cellodextrins. Additionally, when ruminants are fed large amounts of cereal grain along with fiber, ruminal pH can decrease to a point where cellulolytic bacteria no longer grow. A dynamic model based on STELLA software is presented. This model evaluates all of the major aspects of ruminal cellulose degradation: (1) ingestion, digestion and passage of feed particles, (2) maintenance and growth of cellulolytic bacteria and (3) pH effects.

Effects of increasing dietary concentrations of fish oil on lamb performance, ruminal fermentation, and leptin gene expression in perirenal fat

“…Marinova et al (2007) suggested that changes in propionate and acetate are related to the depression of acetate-producing bacteria, which are inhibited by polyunsaturated fatty acids. However, in high-grain diets, these bacteria do not grow (Russell et al, 2009); therefore, the changes in propionate and acetate could be related to effects on the rumen protozoa, because polyunsaturated fatty acids are also toxic to rumen protozoa (Oldick and Firkins, 2000). The microbial defaunation by high-grain diets have similar effects on the fermentation pattern (Mendoza et al, 1993).…”

Rumen microbial (meta)genomics and its application to ruminant production

“…Most of the work on fibre degradation in the rumen is based on three cultivable bacteria: Fibrobacter succinogenes, Ruminococcus albus and Ruminococcus flavefaciens. Because they are able to hydrolyse crystalline cellulose, they were considered to be important in the rumen (Flint et al, 2008;Wallace, 2008;Russell et al, 2009). The genomes of these three bacteria have been sequenced (see 'Rumen microbial genome projects section') and the enzymatic strategies to hydrolyse cellulose used by each species have been partially unravelled.…”

Rumen microorganisms and fermentation

“…Because cellulose is the main component of the cell wall of these plants, cellulolytic ruminal microorganisms play an important role in animal nourishment (Russell et al 2009). Cellulose is digested in the rumen (Michalet-Doreau et al 2002).…”