Cellulose Degradation in the Rumen

Cellulose Breakdown by Microorganisms in the Rumen

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Introduction

A diverse group of microbes live within the digestive systems of ruminants, which include some animals with plant-based diets such as cows, sheep, deer, and goats. The microbes allow the animals to break down complex plant materials such as amino acids, cellulose, starch, and sugars into simpler products that can then be broken down by the animal’s own metabolism. Ruminants have a four-chambered gut, and these microorganisms live primarily in the rumen. One particularly important bacterial genus that takes part in the degradation of cellulose is Ruminococcus. Ruminococcus bacteria break down the plant fiber into the monosaccharide glucose, which can then be further broken down through glycolysis. This symbiotic relationship enables ruminants to digest this fiber without having to encode for more enzymes to do this job in their own genomes. The relationship with microbes provides ruminants with about 15% of their caloric intake. The Ruminococcus genus, which includes Ruminococcus albus and Ruminococcus flavifaciens, is just one of many microbes living in the rumen. Others include Megasphaera, Fibrobacter, Streptococcus, Escherichia, Chytridiomycetes fungi, and methanogens. The proportions of microbes present vary greatly depending upon the diet of the ruminant. For this reason, the diets of the animals greatly impact their own health, and also effects consumers of their meat and the environment as a whole.

Electron micrograph of Ruminococcus bacteria.

The Four Chambered Stomach and Function of Ruminant Microbes

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File:Rumen

The four chambered stomach of ruminants. Microorganisms live primarily in the rumen, but all four chambers are essential for digestion.

Metabolic Pathway

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Factors that Effect the Microbe Population

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Conclusion

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References

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Diez-Gonzalez F, Callway TR, Kizoulis MG, Russel JB. 1998. Grain feeding and the dissemination of acid-resistant Escherichia coli from cattle. Science 281 (5383) 1666-1668.

Leschine SB. 1995. Cellulose degradation in anaerobic environments. Annual Review of Microbiology 49: 399-426.

McAllister TA, Bae HD, Jones GA, Cheng KJ. 1994. Microbial attachment and feed digestion in the rumen. Journal of Animal Science 72(11): 3004-3018.

Ryosuke K, Saburi W, Odaka R, Taguchi H, Ito S, Mori H, Matsui H. 2012. Metabolic mechanism of Mannan in ruminal bacterium, Ruminococcus albus, involving two mannoside phosphorylases and cellobiose 2-epimerase. Journal of Biological Chemistry 287(50): 42389-42399.

Saro C, Ranilla MJ, Carro, MD. 2012. Postprandial changes of fiber-degrading microbes in the rumen of sheep fed diets varying in type of forage as monitored by real-time PCR and automated ribosomal intergenic spacer analysis. Journal of Animal Science 90 (12): 4487-4494.

Slonczewski JL and Foster JW. 2009. Microbiology: An Evolving Science. 2nd Edition. W.W. Norton, New York: 822-825.

Weimer PJ. Cellulose degradation by ruminal microorganisms. 1992. Critical Reviews in Biotechnology 12(3): 189-223.

Edited by KatiePruett, a student of Nora Sullivan in BIOL187S (Microbial Life) in The Keck Science Department of the Claremont Colleges Spring 2013.