Selective inhibition of reactions involved in methanogenesis and fatty acid production on rice roots

Abstract

Washed excised roots of rice (Oryza sativa) produced H(2), CH(4) and fatty acids (millimolar concentrations of acetate, propionate, butyrate; micromolar concentrations of isovalerate, valerate) when incubated under anoxic conditions. Surface sterilization of the root material resulted in the inactivation of the production of CH(4), a strong reduction of the production of fatty acids and a transient (75 h) but complete inhibition of the production of H(2). Radioactive bicarbonate was incorporated into CH(4), acetate, propionate and butyrate. About 20-40% of the fatty acid carbon originated from CO(2) reduction. In the presence of phosphate, CH(4) was exclusively produced from H(2)/CO(2), since phosphate selectively inhibited acetoclastic methanogenesis. Acetoclastic methanogenesis was also selectively inhibited by methyl fluoride, while chloroform or 2-bromoethane sulfonate inhibited CH(4) production completely. Production of CH(4), acetate, propionate and butyrate from H(2)/CO(2) was always exergonic with Gibbs free energies <-20 kJ mol(-1) product. Chloroform inhibited the production of acetate and the incorporation of radioactive CO(2) into acetate. Simultaneously, H(2) was no longer consumed and accumulated, indicating that acetate was produced from H(2)/CO(2). Chloroform also resulted in increased production of propionate and butyrate whose formation from CO(2) became more exergonic upon addition of chloroform. Nevertheless, the incorporation of radioactive CO(2) into propionate and butyrate was inhibited by chloroform. The accumulation of propionate and butyrate in the presence of chloroform probably occurred by fermentation of organic matter, rather than by reduction of acetate and CO(2). [U-(14)C]Glucose was indeed converted to acetate, propionate, butyrate, CO(2) and CH(4). Radioactive acetate, CO(2) and CH(4) were also products of the degradation of [U-(14)C]cellulose and [U-(14)C]xylose. Addition of chloroform and methyl fluoride did not affect the product spectrum of [U-(14)C]glucose degradation. The application of combinations of selective inhibitors may be useful to elucidate anaerobic metabolic pathways in mixed microbial cultures and natural microbial communities.

Soil microbial community structure in a rice paddy field and its relationships to CH4 and N2O fluxes

“…As a consequence of the positive correlation obtained by multivariate statistical analysis between CH 4 emissions and the fatty acid 10Me16:0, it may be possible to hypothesise the presence of methanogens, and consequently their changes depending on soil conditions, by using just the sulfate reducers methylbranched biomarker. Although it is known that sulfate reducers compete with methanogens mainly for H 2 (Chidthaisong , the contribution in rice fields of hydrogenotrophic methanogenesis to total CH 4 production is close to the expected ratio of a third or less (Rothfuss and Conrad 1993;Bilek et al 1999;Conrad and Klose 2000). Thus it is probable that these two anaerobic groups can coexist.…”

Biohydrogen production in granular up‐flow anaerobic sludge blanket (UASB) reactors with mixed cultures under hyper‐thermophilic temperature (70°C)

“…The lack of methanogens in R1 and R2 is likely caused by BES addition during the startup period. BES, a structural analog of co-enzyme M, is often used to inhibit methanogenesis (Conrad and Klose, 2000). In this study, BES was put into R1 and R2 in initial time, so BES could stop the adaptation of the methanogenic bacteria to the granules and make them inactive.…”

Methanogenic Archaea and oral infections – ways to unravel the black box

“…Therefore, in order to mitigate the formation of CH 4 in anaerobic environments and in order to understand the ecology of its formation, a wide range of inhibiting compounds have been investigated (e.g. 63–65). Clearly, in our case methanogenesis per se is not what we need to prevent in periodontal plaque but H 2 -consumption.…”

“…Both reactions however, although at opposite ends of a complex biochemical cascade within methanogens, are tightly linked such that once the final step of CH 4 formation is inhibited, the entire process is blocked. For example, 2-bromoethane sulfonate (BES), which is a structural analogue of coenzyme M, is often used to specifically inhibit methanogenesis (63). Coenzyme M is the C1-carrier, required for the final methyl-transfer reactions in the metabolism of methanogens.…”