Targeting physiological activities to modify the ecology and functionality of rumen and gastrointestinal ecosystems, prototypical anaerobic digester

Authors: Anderson, Robin; RICKE, STEVEN - UNIVERSITY OF ARKANSAS; Krueger, Nathan; Nisbet, David

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 1/25/2009
Publication Date: 4/20/2009
Citation: Anderson, R.C., Ricke, S.C., Krueger, N.A., Nisbet, D.J. 2009. Targeting physiological activities to modify the ecology and functionality of rumen and gastrointestinal ecosystems, prototypical anaerobic digesters. In: Biswas, S., Kaushik, N., Pandey, A., editors. Bioprocess and Bioproducts: Technology Trends and Opportunities. New Delhi, India: Asiatech Publishers Inc. p. 50-65.

Interpretive Summary: In the biotechnology industry, anaerobic fermentation of animal and municipal wastes provides an opportunity to transform low value biomass into higher value products such as ethanol, organic acids, or methane. However, because pathogenic bacteria can reside in animal and municipal wastes, the biotechnology industry is interested in learning how to minimize the potential contamination of end, or byproducts produced during their anaerobic digestion. Additionally, in order to optimize the biochemical conversions that take place in these ecosystems, the biotechnology industry is looking to learn from studies conducted with other microbial ecosystems. Of particular interest is the microbial population inhabiting the cow’s stomach because it also can harbor pathogenic bacteria and is highly regarded for its ability to digest and transform low quality plant material into chemical forms of value for the host animal. In this review, we summarize the development of strategies targeting unique biochemical pathways of pathogenic Salmonella, Escherichia coli, and Campylobacter that have been proven successful in reducing the survivability of these pathogens in the cow’s gut. We also summarize the use of a certain type of chemical known as a nitrocompound to inhibit the energetically wasteful process of methane production that occurs in the cow’s stomach. Another undesirable reaction that occurs within the cow’s stomach is the conversion of beneficial fats to unhealthy fats, and we present results from experiments that show how we can minimize this process. This review will help the biotechnology industry produce safer products at less cost, with the ultimate products derived from these processes being more affordable for the American consumer.

Technical Abstract: The rumen microbial ecosystem is highly regarded for its ability to digest and transform low quality plant material into chemical forms of use by the host. However, less than 35% of the dietary energy consumed by the ruminant is conserved by the host. Methane production within the rumen contributes the loss of up to 15% of the animal’s gross energy intake and, as in certain other anaerobic digesters, contributes significantly to the carbon footprint of this industry. Certain short chain nitrocompounds, such as nitroethane, 2-nitroethanol, and the phytotoxins, 3-nitro-1-propionic acid, and 3-nitro-1-propanol, markedly inhibit ruminal methane production by inhibiting the oxidation of hydrogen and formate, the primary reducing substrates for methanogenesis within the rumen. An attractive aspect of nitro-caused inhibition of methanogenesis is that these inhibitors also consume electrons via their reduction to amines or amino acids, and thus provide the ecosystem an alternative mechanism for the disposal of reducing equivalents generated during glycolysis. Lipolysis within the rumen liberates free fatty acids from dietary lipids thereby making unsaturated fatty acids available for biohydrogenation. Consequently, ruminant-derived foods contain high proportions of saturated fats which are associated with negative-health effects such as coronary heart disease. High concentrations of free long-chain fatty acids also negatively impact digestion via inhibition of cellulolytic bacteria. Addition of glycerol to rumen incubations inhibits rumen lipolysis by as much as 80% suggesting that supplementation of ruminant diets with this common byproduct of biofuel production would exert endproduct inhibition of microbial fat hydrolysis. The ruminant gastrointestinal tract can be a reservoir for certain pathogenic bacteria, thus requiring exporters of ruminant-derived products to implement food security standards. Strategies targeting nitrate respiration of Salmonella and enterohemorrhagic Escherichia coli and targeting amino acid metabolism of Campylobacter, have been proven successful in reducing the survivability of these pathogens in the ruminant gut. Strategies targeting specific physiological activities have successfully modified the ecology and functionality of the rumen ecosystem and may have application in other anaerobic fermentations as well.