Forschungsdaten – Titel und Zusammenfassungen von Publikationen, extrahierte Daten und Katalogeinträge – erscheinen in ihrer Originalsprache Englisch.
Isolation and Characterization of Electrochemically Active Subsurface Delftia and Azonexus Species
Yamini Jangir, Sarah French, Lily Momper, Duane P. Moser +2
KI-Zusammenfassung
72 % KonfidenzThis paper reports electrochemical enrichment and isolation of Delftia and Azonexus strains from a deep subsurface aquifer, demonstrating their ability to transfer electrons to anodes poised at 272–572 mV vs. SHE using acetate as electron donor. The enrichment was performed in a 1 L half-cell reactor with four carbon cloth electrodes at different potentials over 6 months, yielding anodic currents and biofilm formation. Both isolates were confirmed to produce current when tested individually at +522 mV vs. SHE, though absolute current magnitudes were modest. The work extends known EET diversity to Betaproteobacteria families previously suspected but not directly confirmed as electrochemically active.
Zentrale Erkenntnisse
Schwellenwert Anodic current developed within 20 days across all four electrode potentials (272–572 mV vs. SHE), indicating that Delftia and Azonexus can accept electrons across a wide redox potential window.
Was heißt das. When designing bioelectrochemical systems for subsurface or acetate-oxidizing communities, do not assume a narrow operating window; test across 300 mV range to identify the optimal potential for your target organisms.
Mechanismus Abrupt current decrease occurred with every medium change, then recovered, suggesting soluble redox shuttles or transient cell-surface binding dynamics mediate electron transfer rather than purely direct contact.
Was heißt das. Maintain stable medium composition and minimize dilution events in long-term enrichments; if medium must be changed, expect temporary loss of current and plan for recovery time.
Leistung Acetate concentration decreased from 10 to 7.5 mM over 1 month, correlating with anodic current rise, confirming acetate oxidation coupled to electrode reduction.
Was heißt das. Use HPLC monitoring of acetate as a quantitative proxy for anode-respiring activity in enrichments; a 25% drop over 30 days is a realistic benchmark for these organisms.
Mechanismus SEM revealed extracellular filaments morphologically similar to bacterial nanowires, suggesting direct EET mechanisms beyond soluble shuttles may operate in parallel.
Was heißt das. Do not assume a single EET mechanism; design electrochemical experiments to distinguish direct contact (nanowire-like) from indirect (shuttle-mediated) pathways, e.g., by varying electrode spacing or adding shuttle inhibitors.
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Hoch No quantitative current density or power output reported for pure culture isolates; only qualitative 'rise in anodic current' mentioned.
The paper states 'The rise in anodic current upon inoculation was correlated with a modest increase in total protein content' but provides no numerical values (mA, mA/m², W/m²) for either isolate, making it impossible to compare performance to other EET organisms or scale predictions.
Versuch. Perform chronoamperometry with quantified current (mA) and electrode area (cm²) to calculate current density (mA/cm²) and power density (mW/m²) for Delftia WE1-13 and Azonexus WE2-4 at 522 mV vs. SHE.
Hoch No investigation of nitrogen cycling (denitrification, nitrification, N2O production) despite enrichment at potentials (300–750 mV vs. SHE) overlapping nitrate redox couples and despite prior knowledge that Comamonadaceae and Rhodocyclaceae are denitrifiers.
The paper notes 'With acetate as the electron donor and electrodes poised within the redox potential range (300–750 mV vs. SHE) of nitrogen-based redox couples like nitrate in neutral waters' and 'both families have been observed on anodes in previous microbial fuel cell (MFC) enrichments' where 'some members of these families could utilize electrodes as electron acceptors, in the absence of nitrate'. No NO₃⁻, NO₂⁻, or N₂O measurements were performed.
Versuch. Test Delftia WE1-13 and Azonexus WE2-4 in NDW2 medium supplemented with 1–10 mM NO₃⁻ (or NO₃⁻-N basis) at 272–572 mV vs. SHE; measure NO₃⁻, NO₂⁻, N₂O, and N₂ by HPLC/GC to determine if electrode potential shifts denitrification pathway or causes N2O accumulation.
Mittel No systematic variation of cathode potential to identify optimal window for current production or to test trade-offs between current and biomass yield.
Four potentials were tested during enrichment (272–572 mV vs. SHE) but pure culture tests used only one potential (+522 mV vs. SHE). No comparison of current, growth rate, or protein yield across the potential range.
Versuch. Perform chronoamperometry on pure isolates at 272, 372, 472, 522, and 572 mV vs. SHE; plot current density and specific growth rate (µ, h⁻¹) vs. potential to identify peak performance and trade-offs.
Mittel No measurement of dissolved oxygen, pH, or ionic strength in the electrochemical reactor during enrichment; no control for oxygen leakage or pH drift.
The paper states 'Filter-sterilized N₂ gas was used throughout to maintain anaerobic conditions' but provides no dissolved oxygen measurements, pH monitoring, or discussion of potential oxygen contamination. Abiotic control showed no current, but does not rule out microaerobic niches.
Versuch. Monitor dissolved oxygen (Clark electrode or optical probe), pH, and conductivity continuously during enrichment and pure culture tests; perform abiotic controls with and without oxygen to quantify any contribution from aerobic respiration.
Mittel Hydraulic retention time (HRT) not specified; dilution rate stated as 'one reactor volume per day' but no analysis of how HRT affects community composition or current production.
Text states 'The dilution rate in the bioreactor amounted to one reactor volume per day' but does not discuss whether this favors fast-growing or slow-growing organisms, or whether shorter/longer HRT would enrich different EET phenotypes.
Versuch. Repeat enrichment at HRT of 0.5, 1, 2, and 4 days; measure current density, community composition (16S), and isolate diversity to identify HRT-dependent selection.
Niedrig No measurement of C/N ratio or its effect on community composition; acetate concentration fixed at 10 mM with no variation.
The paper uses 10 mM acetate throughout but does not test whether lower or higher acetate concentrations, or different C/N ratios, would shift the enriched community or improve current production.
Versuch. Test acetate concentrations of 1, 5, 10, 20 mM and C/N ratios (acetate:NH₄⁺) of 5:1, 10:1, 20:1 in batch or fed-batch mode; measure current, growth, and community composition.
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Was gemacht wurde
- Systemtyp
- MFC
Was funktioniert hat
Noch keine Ergebniskennzahlen extrahiert.
Zusammenfassung
Continental subsurface environments can present significant energetic challenges to the resident microorganisms. While these environments are geologically diverse, potentially allowing energy harvesting by microorganisms that catalyze redox reactions, many of the abundant electron donors and acceptors are insoluble and therefore not directly bioavailable. Extracellular electron transfer (EET) is a metabolic strategy that microorganisms can deploy to meet the challenges of interacting with redox-active surfaces. Though mechanistically characterized in a few metal-reducing bacteria, the role, extent, and diversity of EET in subsurface ecosystems remains unclear. Since this process can be mimicked on electrode surfaces, it opens the door to electrochemical techniques to enrich for and quantify the activities of environmental microorganisms in situ. Here, we report the electrochemical enrichment of microorganisms from a deep fractured-rock aquifer in Death Valley, CA, USA. In experiments performed in mesocosms containing a synthetic medium based on aquifer chemistry, four working electrodes (WEs) were poised at different redox potentials (272, 373, 472, 572 mV vs. SHE) to serve as electron acceptors, resulting in anodic currents coupled to the oxidation of acetate during enrichment. The anodes were dominated by Betaproteobacteria from the families Comamonadaceae and Rhodocyclaceae. A representative of each dominant family was subsequently isolated from electrode-associated biomass. The EET abilities of the isolated Delftia strain (designated WE1-13) and Azonexus strain (designated WE2-4) were confirmed in electrochemical reactors using WEs poised at 522 mV vs. SHE. The rise in anodic current upon inoculation was correlated with a modest increase in total protein content. Both genera have been previously observed in mixed communities of microbial fuel cell enrichments, but this is the first direct measurement of their electrochemical activity. While alternate metabolisms (e.g., nitrate reduction) by these organisms were previously known, our observations suggest that additional 'hidden' interactions with external electron acceptors are also possible. Electrochemical approaches are well positioned to dissect such extracellular interactions that may be prevalent in the subsurface.
Schlagwörter
Kennungen
- PubMed
- 27242768
- Zeitschrift
- Frontiers in Microbiology
- Jahr
- 2016
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