Effects of methanogenesis and sulfate-reduction on acetogenetic oxidation of propionate and further decomposition of acetate in paddy soil

Abstract

Under laboratory conditions, submerged paddy soil with the addition of propionate was incubated anaerobically. Propionate oxidation was suppressed by the addition of H2, and the specific inhibitor for methanogenesis (2-bromoethanesulfonate; BES). The inhibition with H2 can be associated to the negative feedback of endergonic propionate oxidation with H2. The BES inhibition on propionate oxidation can be attributed to the uncoupling of propionate oxidation and methanogenesis. When sulfate was added, propionate oxidation was not suppressed by the addition of H2, but it was suppressed by the addition of the specific inhibitor for sulfate-reduction (molybdate). These findings suggest the occurrence of preferential coupling of propionate oxidation with sulfate reduction. During the oxidation of propionate after the addition of sulfate, acetate hardly accumulated in the absence of BES, but accumulated in the presence of BES. Propionate oxidation proceeded irrespective of the addition of BES. These findings indicate that the decomposition of acetate, which was produced from propionate, was associated with methanogenesis even in the presence of sulfate, and that electrons flowed through methanogenesis and sulfate-reduction without competition as long as propionate was present.

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

“…Washed excised rice roots (not sterilized) contained about 100^250 WM glucose (Table 2) which was completely consumed within 24 h. Addition of carrier-free [U- 14 C]glucose also resulted in complete consumption within 24 h (Fig. 4) with apparent turnover times of 6 7 h per 10 g fresh roots ( Table 2).…”

“…We assume that glucose was assimilated by the excised roots and/or the microorganisms on the root surface. The inhibitors CHCl 3 6 CH 3 FIphosphate stimulated rather than inhibited the consumption of [U- 14 C]glucose, while the consumption of radioactive acetate and the production of 14 CH 4 was inhibited ( Table 2). Addition of [U- 14 C]cellulose or [U- 14 C]xylose to washed rice roots (carbonate bu¡er) also resulted in rapid conversion of the radioactive compounds to radioactive CO 2 , acetate and ¢nally also CH 4 , which all together accounted for about 20% of the added radioactivity (data not shown).…”

“…The inhibitors CHCl 3 6 CH 3 FIphosphate stimulated rather than inhibited the consumption of [U- 14 C]glucose, while the consumption of radioactive acetate and the production of 14 CH 4 was inhibited ( Table 2). Addition of [U- 14 C]cellulose or [U- 14 C]xylose to washed rice roots (carbonate bu¡er) also resulted in rapid conversion of the radioactive compounds to radioactive CO 2 , acetate and ¢nally also CH 4 , which all together accounted for about 20% of the added radioactivity (data not shown). Similarly as with [U- 14 C]glucose, most of the radioactivity was recovered in the roots at the end of the The roots were incubated in carbonate or phosphate bu¡er, and in the presence or absence of inhibitors (mean þ S.D., n = 3).…”

“…4). After about 200 h of incubation, 14 CH 4 also started to accumulate and radioactive acetate decreased (Fig. 4).…”

“…The fraction of acetate, propionate and butyrate that was produced from reduction of H 14 CO 3 3 was calculated analogously from the speci¢c radioactivities of the fatty acid carbon and the 14 CO 2 assuming that each of the carbon atoms was equally labeled. The turnover times of [U- 14 C]glucose and [U-…”