Methanogenesis inhibitors

Thalib A (2004) In vitro study of effectiveness of saponin from Sapindus rarak fruit as methanogenesis inhibitor on ruminal digestion system. J Dmu Temak Veteriner 9 164-171 (in Indonesiem)... 

Methanogens catalyze this reaction if methanogenesis was blocked by inhibitors of the CH3-S-C0M reductase [105,106],... 

In order to explain the Na stimulation of ATP synthesis driven by a diffusion potential the presence of a Na /H antiporter was proposed [175]. In this artificial system the acidification of the cytoplasm, which occurs in response to electrogenic potassium efflux, could be prevented by the antiporter. Subsequently, Na /H antiporter activity has been demonstrated in both Methanobacterium thermoautotrophicum [176] and in Methanosarcina harden [108]. An important result of these studies was that the Na /H antiporter could be inhibited by amiloride and harmaline, which have been described as inhibitors of eucaryotic Na" /H" antiporters [177]. Using these inhibitors it has been shown that an active antiporter is essential for methanogenesis from H2/CO2 [176,178]. The antiporter also accepts Li instead of Na, since Li stimulates CH4 formation from H2/CO2 in the absence of Na [176]. In subsequent studies the use of amiloride and the more potent derivative ethyl-isopropylamiloride permitted the discrimination of primary and secondary Na potentials generated in partial reactions of the CO2 reduction pathway. 

Despite the lower rate in the presence of inhibitor, radioactively labelled palmitate was added to a CHCla-inhibited system. Table IV shows that butyrate was formed at a faster rate than formate, acetate, or propionate. The fact that butyrate was now one of the major end products of palmitate dissimilation indicates that secondary reactions involving acetate and/or propionate were probably serving to remove hydrogen produced during dissimilation since methanogenesis was inhibited in these experiments. This was partially verified by the findings that radioactively labelled acetate was converted to formate and butyrate at faster rates in inhibited than in uninhibited sludge. It is also possible that formation of butyrate indicates some alternative to -oxidation as a dissimilatory reaction. Acetate itself was formed from C02 in the presence or absence... 

Fig. 5.15 Inhibitor experiment for the demonstration of substrates used by sulfate reducing bacteria in a coastal marine sediment. The concentrations of volatile fatty acids, hydrogen and methane are followed during a time-course experiment over 8 hours. At 3.5 hours (arrow) molybdate was added and the substrates accumulate at a rate corresponding to their rate of consumption before inhibition. The formation of methane shows the release of competition for the common substrates for methanogenesis and sulfate reduction (H and acetate). Data from Sorensen et al. (1981).

Another environmental parameter that is important to methane emissions is soil temperatnre. Soil temperature affects the metabolic activity of microorganisms that prodnce substrates for inhibitors of methanogenesis as well as the methanogens themselves. Temperatnre is directly related to methanogenesis under field conditions (Schutz et al., 1990 Westermann, 1993). Methane emission rates generally parallel soil temperature levels. 

Chan, A. S. K. and T. B. Parkin. 2000. Evaluation of potential inhibitors of methanogenesis and methane oxidation in a landfill cover soil. Soil Biol. Biochem. 32 1581-1590. 

Thymol (0.4 g L" ), the main component of EOs derived from Thymus and Origanum plants, a strong inhibitor of in vitro methane production (Evans and Martin 2000), caused a reduction in methane to the extent of 99% at 6 mM concentration (Macheboeuf et al. 2008). Anethole at 20 mg L of medium caused an inhibition of methane in vitro (Chaves et al. 2008c). Other EOs like. Juniper berry EOs and cinnamon oil (Chaves et al. 2008c) and peppermint oil (Tatsouka et al. 2008 Agarwal et al. 2009) have been shown to have a strong inhibitory effect on methanogenesis. The active component of cinnamon oil i.e. cinnamaldehyde caused a depression in methane production to the extent of 94% at 5 mM (Macheboeuf et al. 2008). Methanol and ethanol extracts of fennel seeds and clove buds inhibited in vitro methane production (Patra et al. 2010). Eucalyptus oil inhibited methane production up to 58% at 1.66 mL L (Kumar et al. 2009), 90.3% at 2 mL L" (Sallam et al. 2009) and 70% at a dose of 0.33 g of a-cyclodextrin-eucalyptus oil complex... 

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