To optimise the synthetic or metabolic pathway of micro-organisms related to methane synthesis by employing modern molecular biotechnology to obtain genetically modified microorganisms. Then the genetically modified micro-organisms are introduced back into the rumen ecosystem to establish a relatively stable microbiota that can replace or compete with the original pathway of methanogenesis, to reduce methane synthesis in the rumen.
Feasibility of technology and operational necessities
The reaction of carbon dioxide and hydrogen to form methane is a key step to decrease the hydrogen partial pressure in the rumen, so finding new hydrogen competitor or methane oxidative pathway could reduce methane production. For example, acetogens can also utilise hydrogen as substrate and have been found to be dominant in kangaroos’ rumen. If acetogens that can out compete methanogens in hydrogen intake are selected by genetically modified technology and then form stable microflora in rumen, less methane would be produced from ruminants. Methane oxidation may be another possible solution to solve this problem. Methanotrophic bacteria can oxidize methane to carbon dioxide, and they inhabit widely diverse environments. Through genetic modification, bacteria with high methane-oxidative efficiency can be obtained. Once these bacteria are introduced into rumen and form stable microflora, methane will be used to form carbon dioxide without affecting ruminal fermentation.
At present, the researchers worldwide engaging in methane emission mitigation of ruminants mainly focus on nutrition regulation, optimisation of feed formula and application of additives. In comparison, the methane mitigation in ruminants using genetic modification is only just now being investigated. This technology, marked by complexity of operation, excessively high up-front investment and long period of study, requires multi-disciplinary cooperation. All these factors together restrict the development of genetic modification of micro-organisms to reduce methane emissions.
Status of the technology and its future market potential
- Improving digestibility, fermentation, energy utilisation efficiency of feed, and animal performance.
- Methanogens and other micro-organisms form symbiotic relationships and benefit mutually (Thiele et al, 1988; Joblin et al, 1989), so introducing genetically modified microbes favours the homeostasis of microbial diversity and complexity of symbiotic relationship in rumen, avoiding side effects onrumen ecosystems.
- Many approaches for reducing methane emissions have been tried, including research on feed preparation, vaccines, and additives (Han et al, 1997; Beauchemin et al, 2005; Yvette et al, 2009; Wright et al, 2004; Machmüller et al, 2001; Animut et al, 2008). However, these approaches lack sustainability and heritability. In comparison, once the genetically modified microbes survive in rumen, they will be carried by ruminants as long as they live and can be inherited by their offspring, without any extra costs to maintain methane mitigation.
- Although chemical inhibitors or antibiotics can reduce methane synthesis, the long-term adoption may cause residues of organic matter or antibiotics in meat and milk and bad health conditions of animals. However, genetic modification of micro-organisms in rumen can eliminate all the adverse effects mentioned above and achieve methane emission reduction on the premise that food security is guaranteed.
In spite of the advantages of genetic modification of rumen micro-organisms in reducing methane emissions in rumen, several problems and technical barriers remain.
- Most of the microorganisms in rumen are hard to isolate or culture. Mutagenic screening and genetic modification require more information on the mechanism and ecological functions of microbial metabolism and are still at a trial stage.
- Relevant reports indicate that technical barriers exist for introducing genetically modified strains into the rumen ecosystem, as well as for establishing a stable microflora and a stable symbiotic relationship (Wallace et al., 1994; Cotta et al., 1997; McSweeney et al., 1994).
How the technology could contribute to socio-economic development and environmental protection
Financial requirements and costs
- Animut G., R. Puchala, and A. L. Goetsch (2008): Methane emission by goats consuming diets with different levels of condensed tannins from lespedeza. Animal Feed Science and Technology 144(3-4):212-227.
- Beauchemin K. A., and S. M. McGinn (2005): Methane emissions from feedlot cattle fed barley or corn diets. Journal of Animal Science, 83: 653-661.
- Cotta M. A., T. R. Whitehead and M. A. Rasmussen. (1997): Survival of the recombinant Bacteroides thetaiotaomicron strain BTX in vitro rumen incubations. Appl Microbiol, 82: 743-750.
- Han J. F., Feng Y. L., Zhang X. M., Mo F., Zhao G.Y. and Yang Y. F.. (1997): Effects of Fiber Digestion and VFA in the Rumen on the Methane Production in Steers of Different Type of Diets. Chinese Journal of Veterinary Science, 17:278-280.
- Joblin, K. N., G. P. Campbell, A. J. Richardson and C. S. Stewart (1989): Fermentation of barley straw by anaerobic rumen bacteria and fungi in axenic culture and in co-culture with methanogens. Ltrs. in Appl. Microbiol. 19:195-197.
- Machmüller A, C.R. Soliva and C.R. Soliva. (2001): Diet composition affects the level of ruminal methane suppression bymedium-chain fatty acids. Australian Journal of Agricultural Research, 713-722.
- McSweeney C S, Mackie R I and White B A. (1994): Transport and intracellular metabolism of major feed compounds by ruminal bacteria: the potential for metabolic manipulation. Aust J Agric Res, 45, 731-756.
- Thiele, J. H. and J.G. Zeikus. (1988): Control of interspecies electron flow during anaerobic digestion: Significance of formate transfer versus hydrogen transfer during syntrophic methanogenesis in flocs. Appl. Environ. Microbiol. 54: 20-29
- Wallace R J. (1994): Ruminat microbiology, biotechnology and ruminant nutrition. J Anim Sci, 72, 2992-3003.
- Wright A. D., P. Kennedy, C. J. Neill, A. F. Toovey, S. Popovski, S. M. Rea, C. L. Pimm and L. Klein. (2004): Reducing methane emissions in sheep by immunization against rumen methanogens. Vaccine, 22, 3976-85.
- Yvette J. W., S. Popovski, S. M. Rea, L. C. Skillman, A. F. Toovey, K. S. Northwood and A. D. Wright. (2009): A Vaccine against Rumen Methanogens Can Alter the Composition of Archaeal Populations. Appl Environ Microbiol, 75:1860-1866.