Perturbation of syntrophic isobutyrate and butyrate degradation with formate and hydrogen

Wu, Wei‐Min; Jain, Mahendra Kumar; Hickey, Robert F.; Zeikus, J. G.

doi:10.1002/(sici)1097-0290(19961105)52:3<404::aid-bit6>3.0.co;2-o

“…Even if we assume that propionate degradation would be uncoupled from ATP synthesis, it should stop at least at a vG s 0. Thus, degradation of butyrate and isobutyrate in a homogeneous syntrophic coculture was completely inhibited by addition of H P causing a positive vG [16]. By contrast, propionate degradation rate constants in anoxic paddy soil decreased gradually with increasing vG.…”

Section: Discussionmentioning

confidence: 93%

Thermodynamics of propionate degradation in methanogenic paddy soil

Krylova

¹

1998

FEMS Microbiology Ecology

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Propionate is syntrophically degraded in methanogenic paddy soil via a randomizing pathway. To study the thermodynamic conditions of this syntrophy, propionate degradation was measured in the presence of different H2 partial pressures (1–20 000 Pa) using methanogenic soil slurries taken from planted Italian paddy soil. The logarithmic decrease of [1‐14C]propionate or [2‐14C]propionate was measured during an incubation period of about 2–3 h to determine degradation rate constants (k). The change of the H2 partial pressure was measured during the same period. Values of k decreased with increasing H2 partial pressures (averaged over the incubation period). However, k was still relatively high, although the Gibbs free energy (ΔG) of syntrophic propionate conversion to acetate, bicarbonate and H2 was already strongly endergonic reaching ΔG values of +60 kJ mol−1 propionate. Assuming propionate conversion to acetate plus formate resulted in the same or even higher ΔG values indicating that this degradation pathway was not realistic. We therefore assume that propionate was degraded within microbial aggregates in which syntrophic propionate degraders were shielded from thermodynamically unfavorable H2 by methanogenic bacteria consuming H2. Gibbs free energies for H2 formation from propionate correlated negatively with the ΔG values for H2 conversion to CH4, but the latter values were generally <−5 kJ mol−1 H2 so that methanogenesis from H2 was always possible. Addition of sulfate did not result in a significant decrease of the ΔG values for H2 formation from propionate demonstrating that H2 consumption by sulfate reducers was not relevant during the short incubation period. Nevertheless, propionate degradation was less strongly inhibited by H2 when sulfate was present indicating that propionate was then mainly degraded by sulfate reduction rather than by syntrophy. The major degradation product of [2‐14C]propionate was 14C‐acetate (followed by 14CO2 and 14CH4) showing that the sulfate reducers oxidized propionate primarily to acetate, bicarbonate and H2. As a conceptual model we therefore speculate that propionate was degraded within methanogenic bacterial aggregates both in the presence and the absence of sulfate and that propionate degraders operated either as sulfate reducers or as H2‐producing syntrophs.

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“…Even if we assume that propionate degradation would be uncoupled from ATP synthesis, it should stop at least at a ΔG>0. Thus, degradation of butyrate and isobutyrate in a homogeneous syntrophic coculture was completely inhibited by addition of H 2 causing a positive ΔG [16]. By contrast, propionate degradation rate constants in anoxic paddy soil decreased gradually with increasing ΔG.…”

Section: Discussionmentioning

confidence: 93%

Thermodynamics of propionate degradation in methanogenic paddy soil

Krylova

¹

,

Conrad

²

1998

FEMS Microbiology Ecology

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Propionate is syntrophically degraded in methanogenic paddy soil via a randomizing pathway. To study the thermodynamic conditions of this syntrophy, propionate degradation was measured in the presence of different H2 partial pressures (1–20 000 Pa) using methanogenic soil slurries taken from planted Italian paddy soil. The logarithmic decrease of [1‐14C]propionate or [2‐14C]propionate was measured during an incubation period of about 2–3 h to determine degradation rate constants (k). The change of the H2 partial pressure was measured during the same period. Values of k decreased with increasing H2 partial pressures (averaged over the incubation period). However, k was still relatively high, although the Gibbs free energy (ΔG) of syntrophic propionate conversion to acetate, bicarbonate and H2 was already strongly endergonic reaching ΔG values of +60 kJ mol−1 propionate. Assuming propionate conversion to acetate plus formate resulted in the same or even higher ΔG values indicating that this degradation pathway was not realistic. We therefore assume that propionate was degraded within microbial aggregates in which syntrophic propionate degraders were shielded from thermodynamically unfavorable H2 by methanogenic bacteria consuming H2. Gibbs free energies for H2 formation from propionate correlated negatively with the ΔG values for H2 conversion to CH4, but the latter values were generally <−5 kJ mol−1 H2 so that methanogenesis from H2 was always possible. Addition of sulfate did not result in a significant decrease of the ΔG values for H2 formation from propionate demonstrating that H2 consumption by sulfate reducers was not relevant during the short incubation period. Nevertheless, propionate degradation was less strongly inhibited by H2 when sulfate was present indicating that propionate was then mainly degraded by sulfate reduction rather than by syntrophy. The major degradation product of [2‐14C]propionate was 14C‐acetate (followed by 14CO2 and 14CH4) showing that the sulfate reducers oxidized propionate primarily to acetate, bicarbonate and H2. As a conceptual model we therefore speculate that propionate was degraded within methanogenic bacterial aggregates both in the presence and the absence of sulfate and that propionate degraders operated either as sulfate reducers or as H2‐producing syntrophs.

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“…Gibbs free energies (Δ G ) of the individual reactions were calculated from the standard Gibbs free energies (Δ G °) and the actual concentrations of reactants and products as described previously [28,41]. The standard Gibbs free energies (Δ G °) of the reactions were calculated from the standard Gibbs free energies of formation ( G f °) of the reactants and products using literature data [46–48].…”

Section: Methodsmentioning

confidence: 99%

Fermentation pattern of methanogenic degradation of rice straw in anoxic paddy soil

Glissmann

¹

,

Conrad

²

2000

FEMS Microbiology Ecology

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The anaerobic degradation of different fractions of rice straw in anoxic paddy soil was investigated. Rice straw was divided up into stem, leaf sheath and leaf blade. The different straw fractions were mixed with paddy soil and incubated under anoxic conditions. Fermentation of straw components started immediately and resulted in transient accumulation of acetate, propionate, butyrate, isobutyrate, valerate, isovalerate and caproate with much higher concentrations in the presence than in the absence of straw. Also some unidentified compounds with UV absorption could be detected. The maximum concentrations of these compounds were different when using different straw fractions, suggesting differences in the degradation pathway of these straw fractions during the early phase of incubation, i.e. with Fe(III) and sulfate serving as oxidants. When concentrations of the intermediates decreased to background values, CH(4) production started. Rates of CH(4)unamended soil. During the methanogenic phase, the percentage contribution of fermentation products to CH(4) production was determined by inhibition with 2-bromoethanesulfonate (BES). Acetate (48-83%) and propionate (18-28%) were found to be the main intermediates of the carbon flow to CH(4), irrespective of the fraction of the rice straw or its absence. Mass balance calculations showed that 84-89% of CH(4) was formed via acetate in the various incubations. Radiotracer experiments showed that 11-27% of CH(4) was formed from H(2)/CO(2), thus confirming that acetate contributed 73-89% to methanogenesis. Our results show that the addition of rice straw and the fraction of the straw affected the fermentation pattern only in the early phase of degradation, but had no effect on the degradation pathway during the later methanogenic phase.

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Perturbation of syntrophic isobutyrate and butyrate degradation with formate and hydrogen

Cited by 26 publications

References 24 publications

Thermodynamics of propionate degradation in methanogenic paddy soil

Thermodynamics of propionate degradation in methanogenic paddy soil

Thermodynamics of propionate degradation in methanogenic paddy soil

Fermentation pattern of methanogenic degradation of rice straw in anoxic paddy soil

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