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Enhancement of methanogenesis by electric syntrophy with biogenic iron-sulfide minerals.

ABSTRACT: Recent studies have shown that interspecies electron transfer between chemoheterotrophic bacteria and methanogenic archaea can be mediated by electric currents flowing through conductive iron oxides, a process termed electric syntrophy. In this study, we conducted enrichment experiments with methanogenic microbial communities from rice paddy soil in the presence of ferrihydrite and/or sulfate to determine whether electric syntrophy could be enabled by biogenic iron sulfides. Although supplementation with either ferrihydrite or sulfate alone suppressed methanogenesis, supplementation with both ferrihydrite and sulfate enhanced methanogenesis. In the presence of sulfate, ferrihydrite was transformed into black precipitates consisting mainly of poorly crystalline iron sulfides. Microbial community analysis revealed that a methanogenic archaeon and iron- and sulfate-reducing bacteria (Methanosarcina, Geobacter, and Desulfotomaculum, respectively) predominated in the enrichment culture supplemented with both ferrihydrite and sulfate. Addition of an inhibitor specific for methanogenic archaea decreased the abundance of Geobacter, but not Desulfotomaculum, indicating that Geobacter acquired energy via syntrophic interaction with methanogenic archaea. Although electron acceptor compounds such as sulfate and iron oxides have been thought to suppress methanogenesis, this study revealed that coexistence of sulfate and iron oxide can promote methanogenesis by biomineralization of (semi)conductive iron sulfides that enable methanogenesis via electric syntrophy.

SUBMITTER: Kato S

PROVIDER: S-EPMC6436484 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Enhancement of methanogenesis by electric syntrophy with biogenic iron-sulfide minerals.

Kato Souichiro S Igarashi Kensuke K

MicrobiologyOpen 20180606 3

Recent studies have shown that interspecies electron transfer between chemoheterotrophic bacteria and methanogenic archaea can be mediated by electric currents flowing through conductive iron oxides, a process termed electric syntrophy. In this study, we conducted enrichment experiments with methanogenic microbial communities from rice paddy soil in the presence of ferrihydrite and/or sulfate to determine whether electric syntrophy could be enabled by biogenic iron sulfides. Although supplementa ...[more]

PMID: 29877051

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Project description:The effects of soil minerals on chromate (CrVIO42-, noted as Cr(VI)) reduction by sulfide were investigated in the pH range of 7.67 to 9.07 under the anoxic condition. The examined minerals included montmorillonite (Swy-2), illite (IMt-2), kaolinite (KGa-2), aluminum oxide (gamma-Al2O3), titanium oxide (TiO2, P-25, primarily anatase), and silica (SiO2). Based on their effects on Cr(VI) reduction, these minerals were categorized into three groups: (i) minerals catalyzing Cr(VI) reduction - illite; (ii) minerals with no effect - Al2O3; and (iii) minerals inhibiting Cr(VI) reduction- kaolinite, montmorillonite, SiO2 and TiO2 . The catalysis of illite was attributed primarily to the low concentration of iron solubilized from the mineral, which could accelerate Cr(VI) reduction by shuttling electrons from sulfide to Cr(VI). Additionally, elemental sulfur produced as the primary product of sulfide oxidation could further catalyze Cr(VI) reduction in the heterogeneous system. Previous studies have shown that adsorption of sulfide onto elemental sulfur nanoparticles could greatly increase sulfide reactivity towards Cr(VI) reduction. Consequently, the observed rate constant, kobs, increased with increasing amounts of both iron solubilized from illite and elemental sulfur produced during the reaction. The catalysis of iron, however, was found to be blocked by phenanthroline, a strong complexing agent for ferrous iron. In this case, the overall reaction rate at the initial stage of reaction was pseudo first order with respect to Cr(VI), i.e., the reaction kinetics was similar to that in the homogeneous system, because elemental sulfur exerted no effect at the initial stage prior to accumulation of elemental sulfur nanoparticles. In the suspension of kaolinite, which belonged to group (iii), an inhibitive effect to Cr(VI) reduction was observed and subsequently examined in more details. The inhibition was due to the sorption of elemental sulfur onto kaolinite, which reduced or completely eliminated the catalytic effect of elemental sulfur, depending on kaolinite concentration. This was consistent with the observation that the catalysis of externally added elemental sulfur (50 muM) on Cr(VI) reduction would disappear with a kaolinite concentration of more than 5.0 g/L. In kaolinite suspension, the overall reaction rate law was:-d[Cr(VI)]/dt = kobs[H+]2[Cr(VI)][HS-]0.70.

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Enhancement of methanogenesis by electric syntrophy with biogenic iron-sulfide minerals.

Publications

Enhancement of methanogenesis by electric syntrophy with biogenic iron-sulfide minerals.

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