Methanogenesis inhibition

Sierra-Alvarez R, I Cortinas, U Venal, JA Field (2004) Methanogenesis inhibited by arsenic compounds. Appl Environ Microbiol 70 5688-5691. 

Nandan, R., Tondwalkar, V., and Ray, R.K., Biomethanation of spent wash Heavy metal inhibition of methanogenesis in synthetic medium, J Ferment Bioeng, 69 (5), 276-281, 1990. 

The standard free energy change for methanogenesis from hydrogen and CO2 is more exergonic than that of acetogenesis (AG o = -135.6kJ per mole methane and AG o = -104.6kJ per mole acetate, respectively). However, certain conditions compromise or inhibit methanogenesis (Fig. 13.5). In a complex ecosystem, the metabolic interactions of the anaerobic populations... 

Anaerobic treatment of high-strength wastewater containing high sulfate poses several unique problems. The conversion of sulfate to sulfide inhibits methanogenesis in anaerobic treatment processes and thus reduces the overall performance efficiency of the system. Treatment of high sulfate pharmaceutical wastewater via an anaerobic baffled reactor coupled... 

A control loop based on H2 measurements has been set up by Lloyd and Whitmore [243] and Whitmore et al. [457] in order to prevent inhibition of methanogenesis they controlled the addition of the carbon source to a thermophilic anaerobic digestion process. Even linked p02, pH and OUR control are reported based on direct mass spectrometric measurements [103,312]. 

Cobamides or corrinoids are involved in methyl-transfer reactions in the methanogenic pathways, especially from methyl substrates [143-156]. At least one cobamide is involved in methanogenesis from H2-CO2 by M. thermoautotrophicum, where it is found in the methyl-H4MPT CoM methyltransferase [157]. The majority are either associated with membranes or bound to soluble proteins [143,158]. Methanogens are inhibited by corrinoid antagonists, suggesting an important metabolic role [159]. 

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. 

A second site for ATP synthesis in acetate fermentation appears be the oxidation of the enzyme-bound CO to CO2. This was deduced from the following findings cell suspensions of Methanosarcina barkeri catalyze the oxidation of free CO to CO2 with as electron acceptor, when methanogenesis is inhibited by bromoethanesulfonate [233] ... 

Methanogenesis is inhibited by O2. This is evident from field studies that show no overlap in the depth distributions of O2 penetration in soils or sediments and net CH4 production. Inhibition by O2 is one reason that water table depth in soils is often a strong predictor of CH4 emissions (Kettunen et al., 1999 Roulet and Moore, 1995 Sundh et al., 1995), the other reason being its influence on CH4 oxidation. 

Laboratory incubations of wetland soils with nitrogen and phosphorus amendments have shown either no elfect or an inhibitory effect on methanogenesis (Bodelier et al., 2000a,b Bridgham and Richardson, 1992 Wang and Lewis, 1992). A low rate of phosphate supply to rice roots stimulated CH4 emission (Lu et al., 1999), while phosphate concentrations 20mM specifically inhibited acetotrophic methanogenesis (Conrad et al., 2000). 

A wide variety of evidence suggests that carbon availability limits methanogenesis in situ. The fact that methanogenesis is often inhibited by the presence of alternative electron acceptors such as Fe(lll) and SO is evidence of competition for fermentation products and thus widespread carbon limitation of the process (Section 8.08.8). 

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