Forschungsdaten – Titel und Zusammenfassungen von Publikationen, extrahierte Daten und Katalogeinträge – erscheinen in ihrer Originalsprache Englisch.
Sulfate-Reducing ElectroAutotrophs and Their Applications in Bioelectrochemical Systems
Valeria Agostino, Miriam A. Rosenbaum
KI-Zusammenfassung
72 % KonfidenzThis mini-review surveys electroautotrophic sulfate-reducing bacteria (SRM) in bioelectrochemical systems, focusing on their cathodic applications for CO₂ fixation. Key pure cultures (Desulfosporosinus orientis, Desulfovibrio piger, Desulfopila corrodens IS4, Desulfobacterium autotrophicum HRM2) operate at cathode potentials of −0.31 to −0.5 V vs. SHE—more positive than the H₂ evolution threshold—enabling direct electron uptake. Mixed-culture biocathodes achieve sulfate reduction rates up to 5.6 g L⁻¹ day⁻¹ at −1.1 V vs. SHE, H₂ production of 2.7 m³ m⁻³ day⁻¹, and enhanced microbial electrosynthesis through syntrophic coupling with acetogens and methanogens. The paper identifies two electron uptake pathways: direct (via outer-membrane cytochromes and nanowires in cytochrome-rich SRM) and indirect (H₂/formate-mediated in cytochrome-poor archaea and Clostridia).
Zentrale Erkenntnisse
Schwellenwert Electroautotrophic SRM operate at cathode potentials (−0.31 to −0.5 V vs. SHE) significantly more positive than abiotic H₂ evolution (−0.41 V vs. SHE), indicating direct electron uptake rather than H₂-mediated metabolism.
Was heißt das. Operators should target potentials in the −0.3 to −0.5 V range to select for direct-uptake SRM and avoid wasting energy on abiotic H₂ production in pure or enriched cultures.
Zielkonflikt Mixed-culture sulfate-reduction rate increased 280-fold from 0.02 g L⁻¹ day⁻¹ (Ecath = −0.2 V) to 5.6 g L⁻¹ day⁻¹ (Ecath = −1.1 V), but coulombic efficiency for sulfate dropped from 72% to 78% (slight gain), suggesting competing reactions at very negative potentials.
Was heißt das. Pushing cathode potential below −0.9 V yields diminishing returns in efficiency; balance rate demand against energy cost and competing side reactions (e.g., H₂ evolution, methanogenesis).
Mechanismus Co-culture of D. corrodens IS4 (high electron-uptake SRM) with M. maripaludis (methanogen) produced methane 20-fold faster (0.6–1.2 µmol h⁻¹ cm⁻²) than pure M. maripaludis (0.05 µmol h⁻¹ cm⁻²) at comparable potentials, via H₂-mediated syntrophy.
Was heißt das. Design mixed biocathodes pairing efficient SRM electron-uptakers with non-electroactive bioproducers; this allows lower potentials (−0.4 V) and better volumetric utilization than pure cultures.
Mechanismus Cytochrome-rich SRM (Deltaproteobacteria, Nitrospirae) likely use direct electron uptake via outer-membrane multiheme c-cytochromes and nanowires, while cytochrome-poor SRM (Archaea, Clostridia) rely on indirect H₂/formate-mediated pathways, but D. orientis (cytochrome-poor) also shows direct uptake at −0.31 V.
Was heißt das. Do not assume cytochrome content predicts electron uptake mechanism; screen candidate strains electrochemically at potentials >−0.4 V to identify direct-uptake phenotypes regardless of phylogeny.
Zielkonflikt SRM-enriched biocathodes for H₂ production require sulfate limitation to suppress sulfate reduction and favor fermentative H₂ production, but sulfate must not be completely absent to avoid H₂S/H₂ off-gas mixtures.
Was heißt das. Maintain a narrow sulfate window (not specified in paper) during H₂ production; implement gas-phase H₂S/H₂ separation or scrubbing for practical deployment.
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Hoch No study reports the minimum sulfate concentration required to suppress H₂S/H₂ off-gas formation while maintaining fermentative H₂ production in SRM biocathodes.
Section 'Hydrogen Production' states 'sulfate concentration in the catholyte of SRM-based MEC has to be limited' but provides no quantitative threshold or operating window (e.g., 0.1–1 mM SO₄²⁻).
Versuch. Vary initial sulfate concentration (0, 0.1, 0.5, 1, 5, 10 mM) in SRM-enriched MEC at fixed Ecath = −0.7 V; measure H₂ production rate, H₂S/H₂ ratio in headspace, and sulfate reduction rate.
Hoch No direct comparison of electron uptake kinetics (current density, overpotential) between cytochrome-rich and cytochrome-poor SRM under identical conditions.
Figure 1B,C and Section 'Direct Mechanism' propose different EEU mechanisms but do not quantify rate differences. D. orientis (cytochrome-poor) achieves direct uptake at −0.31 V, same as D. piger (cytochrome-rich), but no kinetic data provided.
Versuch. Electrochemical impedance spectroscopy and chronoamperometry on pure cultures of D. orientis, D. piger, and D. corrodens IS4 at potentials −0.2 to −0.5 V vs. SHE; extract charge-transfer resistance and maximum current density.
Mittel No systematic study of the effect of catholyte pH on SRM electroautotrophy and product selectivity (H₂ vs. sulfate reduction vs. acetate).
Jafary et al. 2017 operated at pH 4 (acidic) and achieved 1.85 m³ H₂/(m³·d), but all other studies use neutral or near-neutral pH. No pH-dependent mechanism or trade-off is discussed.
Versuch. Operate SRM-enriched MEC at pH 4, 6, 7, 8 with fixed Ecath = −0.7 V; measure H₂ production rate, sulfate reduction rate, and coulombic efficiency to identify optimal pH window.
Mittel No investigation of N₂O or nitrite accumulation in SRM-based biocathodes, despite nitrate-reducing bacteria being listed as electroautotrophs in the abstract.
Abstract mentions 'nitrate-reducing bacteria' as electroautotrophs, but the entire paper focuses on sulfate reduction and H₂/acetate production. No nitrogen cycling data provided.
Versuch. Inoculate SRM-enriched biocathode with mixed culture containing nitrate-reducing bacteria; operate at Ecath = −0.4 to −0.7 V with 10–50 mM NO₃⁻; measure NO₃⁻, NO₂⁻, N₂O, and N₂ concentrations over time.
Mittel No data on the effect of current density or applied potential on the ratio of direct vs. indirect electron uptake in mixed SRM communities.
Section 'Extracellular Electron Uptake in SRM' describes both mechanisms but does not quantify their relative contribution as a function of Ecath or current density in the same reactor.
Versuch. Operate mixed SRM biocathode at constant Ecath = −0.3, −0.4, −0.5, −0.6 V vs. SHE; measure abiotic H₂ production rate (via gas chromatography) and microbial current (via chronoamperometry); calculate H₂-mediated vs. direct electron uptake contribution.
Mittel No comparison of SRM-based biocathodes with acetogenic or methanogenic biocathodes at identical potentials and operating conditions to quantify relative electron uptake rates and product yields.
Paper states 'low rate EEU of electroautotrophic acetogens and methanogens still constitute a big limit' but provides no head-to-head kinetic comparison with SRM under the same conditions.
Versuch. Operate parallel MEC reactors inoculated with pure D. corrodens IS4, Sporomusa ovata, and M. maripaludis at Ecath = −0.4 V vs. SHE; measure current density, product formation rate, and coulombic efficiency.
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Zusammenfassung
Electroautotrophs are microbes able to perform different biocathodic reactions by using CO2 as sole carbon source and electrochemical reducing power as a sole energy source. Electroautotrophy has been discovered in several groups of microorganisms, including iron-oxidizing bacteria, iron-reducing bacteria, nitrate-reducing bacteria, acetogens, methanogens and sulfate-reducing bacteria. The high diversity of electroautrophs results in a wide range of Bioelectrochemical Systems (BES) applications, ranging from bioproduction to bioremediation. In the last decade, particular research attention has been devoted towards the discovery, characterization and application of acetogenic and methanogenic electroautotrophs. Less attention has been given to autotrophic sulfate-reducing microorganisms, which are extremely interesting biocatalysts for multiple BES technologies, with concomitant CO2 fixation. They can accomplish water sulfate removal, hydrogen production and, in some case, even biochemicals production. This mini-review gives a journey into electroautotrophic ability of sulfate-reducing bacteria and highlights their possible importance for biosustainable applications. More specifically, general metabolic features of autotrophic sulfate reducers are introduced. Recently discovered strains able to perform extracellular electron uptake and possible molecular mechanisms behind this electron transfer capacity are explored. Finally, BES technologies based on sulfate-reducing electroautotrophs are illustrated.
Schlagwörter
Kennungen
- Zeitschrift
- Frontiers in Energy Research
- Jahr
- 2018
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