How specific is the inhibition by methyl fluoride of acetoclastic methanogenesis in anoxic rice field soil?

Abstract

Acetoclastic methanogens have been described to be inhibited at much lower concentrations of methyl fluoride, CH3F, than H2/CO2‐utilizing methanogens. Therefore, we tested whether CH3F inhibition may be used to determine, in anoxic rice field soil, the contribution of H2/CO2‐dependent methanogenesis to the total CH4 production by comparing this technique with the incorporation of 14CO2 into CH4. In general, addition of 0.01–1% CH3F to the gas phase resulted in an immediate partial inhibition of the total CH4 production which lasted for at least 200 h. Inhibition increased with the logarithm of the initial CH3F concentration up to about 0.2–0.6%. The initial CH3F concentration slowly decreased with time, probably due to decomposition. CH4 production sometimes completely recovered during the course of the experiment. The presence of CH3F resulted in the accumulation of acetate, the final concentration of which was usually stoichiometrically related to the deficit in CH4 production and increased with the initial CH3F concentration. In some experiments, acetate accumulation was larger than expected from the CH4 deficit and a substantial incorporation of 14CO2 into acetate was observed. Hydrogen, on the other hand, was only slightly elevated in the presence of CH3F. Addition of increasing CH3F resulted in an increase of the percentage of H2‐dependent methanogenesis (measured by conversion of 14CO2 to 14CH4) demonstrating that acetoclastic methanogenesis was preferentially inhibited by CH3F. However, the conversion of 14CO2 to 14CH4 was also slightly inhibited by CH3F. Apparently, CH3F inhibited the H2‐dependent methanogenesis to some extent, depending on the concentration of CH3F applied. Indeed, the ratio between the residual CH4 production rate and the fraction of CH4 produced from 14CO2 decreased with an increasing CH3F concentration. A ratio of unity was obtained at initial CH3F concentrations of 0.2–0.6% (58–174 μM). Both methods, i.e. inhibition using 0.5% CH3F and conversion of 14CO2 to 14CH4, were applied to determine the temporal change of the contribution of H2/CO2‐dependent methanogenesis to the total CH4 production in two different batches of Italian rice field soil during a 120‐days anoxic incubation period. The results of the two methods agreed well within the error of the methods and showed a relatively constant contribution of H2/CO2‐dependent methanogenesis of about 25–30% as soon as CH4 was produced at a steady rate and H2 partial pressures had stabilized at about 1.5–2.5 Pa.

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

“…Also, the capacity for fatty acid synthesis from CO 2 was more pronounced on the rice roots than in the soil. In the soil, incorporation of CO 2 into acetate only became apparent after inhibition of methanogenesis [22]. The rather high potential activity of microorganisms on rice roots is consistent with the observation that a signi¢cant percentage of the CO 2 that is photoassimilated by the plants is released by the roots and converted to CH 4 [373 9].…”

Syntrophobacteraceae‐affiliated species are major propionate‐degrading sulfate reducers in paddy soil

“…S1), including an unamended control (Control), and treatments with gypsum (Gypsum), with propionate (Propionate), with propionate followed by propionate plus gypsum (P2PG), with propionate followed by propionate plus gypsum plus methyl fluoride (P2PGF), with propionate followed by propionate plus gypsum plus fluoroacetate (P2PGA) and with propionate plus gypsum followed by propionate only (PG2P). Methyl fluoride served as specific inhibitor of acetoclastic methanogenesis (Conrad and Klose, 1999), fluoroacetate of acetate consumption by both methanogens and SRB (Chidthaisong and Conrad, 2000). The two soils were chosen, as their physicochemical properties were different and as their archaeal and bacterial community structures have been investigated before (Kruger et al, 2005;Breidenbach and Conrad, 2015;Hernandez et al, 2015).…”

“…After the depletion of propionate, both about 60 mmol gypsum and propionate were added 2-3 times to replenish their concentrations. Methyl fluoride served as specific inhibitor of acetoclastic methanogenesis (Conrad and Klose, 1999), fluoroacetate of acetate consumption by both methanogens and SRB (Chidthaisong and Conrad, 2000). In order to differentiate microbial guilds essential in propionate degradation from those in acetate utilization, two treatments with inhibitors were set up.…”

Vertical distribution of structure and function of the methanogenic archaeal community in Lake Dagow sediment

“…However, we assume that the f CO2 values obtained from the isotopic mass balance (Eq. 3) are more robust, as they are not critically dependent on the correct dosage of CH 3 F, which, however, is critical for the determination of f CO2 by the extent of inhibition of CH 4 production (Conrad and Klose, 1999).…”

“…The concentration of CH 3 F was optimized by measuring the extent of inhibition and the recovery of acetate at the end of the incubation (Frenzel and Bosse, 1996;Conrad and Klose, 1999).…”