Methanogenesis Of Methane

Introduction

Methane in the earth atmosphere is an important greenhouse gas with global warming potential 23 times greater than carbon dioxide and considerable evidence of climate change is also associated with emission of greenhouse gases (GHG), mainly carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), in the atmosphere (IPCC, 2007). The primary sources of methane emission may be divided into natural (30%) and anthropogenic (70%) (Wuebbles & Hayhoe, 2001). Among the anthropogenic factors agriculture, including animal production is a major sector with highly significant contribution to environmental pollution. According to Steinfeld et al. (2006), 80 million tonnes of methane is released annually to the atmosphere from animal production

Methanogens are phylogenetically distinct from both eukaryotes and bacteria, although exist in close association with anaerobic bacteria. Methanogenesis involves in the uptake of hydrogen and stepwise reduction of carbon dioxide. There are three major substrates used by methanogens to produce methane, carbon dioxide, compounds containing methyl group or acetate (Liu and Whitman, 2008). In the rumen, the major pathway uses CO2 as the carbon source and H2 as the main electron donor. Formate also serves as a substrate for ruminal methanogenesis but most of the formate is converted to H2 and CO2 prior to methanogenesis. Methylamine and methanol produced in the rumen also be used for methane production by methylotrophic methanogens of the order methanosarcinales and methanosphaera sps. from the methanobacteriales. Methane is also produced from acetate via aceticlastic pathway by methanosarcinales. The anaerobic conversion of organic matter to methane in the rumen involves a consortium of rumen microorganism with final step lead by methanogens. However, methanogens do not produce fibrolytic enzymes they enhance the energy efficiency and extend the fiber digestion by other microbes. The nature and rate of fermentation of carbohydrates influence the proportion of individual VFA formed and thereby the amount of CH4 produced in the

Therefore, reducing ruminal methane production is not only improves the efficiency of nutrient utilization but also helps to protect the environment from warming. Manipulating the rumen microbial ecosystem to reduce methane emission by ruminants to improve their performance are important issues for animal nutritionists. There is a need to reduce methanogensis by promoting a shift in fermentation pattern towards appropriate metabolic production as well as most economic and long term effective without making an adverse effect on animal and consumers. Inhibition of ruminal CH4 production may improve the efficiency of ruminal fermentation as well as decreasing the atmospheric concentration of a greenhouse