Forschungsdaten – Titel und Zusammenfassungen von Publikationen, extrahierte Daten und Katalogeinträge – erscheinen in ihrer Originalsprache Englisch.
Extracellular electron transfer-dependent anaerobic oxidation of ammonium by anammox bacteria
Dario Rangel Shaw, Muhammad Ali, Krishna P. Katuri, Jeffrey A. Gralnick +5
KI-Zusammenfassung
82 % KonfidenzThis study demonstrates that phylogenetically distant anammox bacteria (Brocadia, Scalindua, Kuenenia stuttgartiensis) can couple anaerobic ammonium oxidation to extracellular electron transfer (EET) using electrodes or graphene oxide as terminal electron acceptors, without requiring nitrite or nitrate. The process oxidizes NH4+ to N2 via hydroxylamine (NH2OH) as an intermediate, achieving 87.8 ± 3.2% coulombic efficiency at 0.6 V vs. SHE with no accumulation of NO2− or NO3−. This opens a pathway for energy-efficient nitrogen removal in bioelectrochemical systems.
Zentrale Erkenntnisse
Schwellenwert Maximum current density and biofilm formation occurred at 0.6 V vs. SHE; no biofilm or current was observed at potentials ≤0.2 V vs. SHE, establishing a critical potential threshold for electrode-dependent anammox.
Was heißt das. Operators must maintain anode potential ≥0.3 V vs. SHE to sustain EET-dependent anammox; lower potentials will not support biofilm establishment or current generation.
Mechanismus The electrode-dependent pathway produces NH2OH as the primary intermediate (not NO), and uses OH− from water molecules rather than NO2−-derived intermediates, as evidenced by 15NH2OD accumulation in D2O experiments.
Was heißt das. Design bioelectrochemical systems to maintain adequate water availability and pH buffering to sustain OH− generation; this pathway differs fundamentally from traditional anammox and may require different pH control strategies.
Leistung Coulombic efficiency was 87.8 ± 3.2% across all NH4+ concentrations and anammox cultures tested, with electron transfer stoichiometry matching 6 electrons per 2 NH4+ oxidized to N2 (Eq. 1).
Was heißt das. Use 87.8% CE as a baseline for energy recovery calculations in full-scale EET-dependent anammox systems; this high efficiency suggests minimal side reactions or competing pathways.
Zielkonflikt Addition of NO2− immediately suppressed current generation and shifted metabolism back to traditional anammox (ΔNO2−/ΔNH4+ = 1.0–1.3, ΔNO3−/ΔNH4+ = 0.12–0.18), indicating anammox bacteria preferentially use soluble electron acceptors over electrodes.
Was heißt das. In mixed-feed systems containing both NO2− and electrodes, anammox will preferentially consume NO2−, limiting current generation; maintain NO2− ≤ detection limit to maximize EET-dependent pathway utilization.
Mechanismus Cyclic voltammetry revealed midpoint potentials (E1/2) of −0.01 ± 0.05 V vs. SHE for all three anammox species, consistent with cytochrome-based direct EET (not soluble mediators), contrasting with prior nitrifying bioelectrochemical systems operating at 0.73 ± 0.06 V vs. SHE.
Was heißt das. EET-dependent anammox operates at much lower potentials than nitrifying systems; this may reduce energy input requirements but requires electrode materials stable at low potentials and biofilms capable of direct electron transfer.
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Mittel No systematic variation of applied potential between 0.2 and 0.6 V vs. SHE to map the full current density vs. potential curve and identify the minimum potential for sustained activity.
Paper shows no biofilm at ≤0.2 V and maximum current at 0.6 V, but intermediate potentials (0.3–0.5 V) are only shown as discrete points in Fig. 2a without detailed kinetic analysis. This gap prevents optimization of energy input.
Versuch. Chronoamperometry at 0.25, 0.35, 0.45, 0.55 V vs. SHE with mature biofilm; measure current density, NH4+ removal rate, and biofilm thickness over 7 days.
Mittel No investigation of cathode potential or cathodic reaction (H2 evolution) effects on overall system energy balance, despite brief mention that single vs. double-chamber MECs showed no difference.
Text states 'there was no significant difference in NH4+ oxidation and current production between the different reactor configurations' but provides no data on H2 production, cathode potential, or overall cell voltage. This is critical for energy efficiency assessment.
Versuch. Operate paired single- and double-chamber MECs at 0.6 V anode potential; measure cathode potential, H2 production rate, and overall cell voltage; calculate net energy input vs. current output.
Mittel No testing of different NH4+ concentrations to establish the operating window and kinetic parameters (Km, Vmax) for EET-dependent anammox.
Fig. 2a shows current is 'proportional to NH4+ concentration' but only tests one concentration (4 mM) in detail. No Monod kinetics, substrate inhibition, or minimum viable concentration are reported.
Versuch. Feed MEC with NH4+ ranging 0.5–10 mM; measure steady-state current density and removal rate; fit to Monod equation to extract Km and Vmax.
Hoch No measurement of N2O or NO accumulation during EET-dependent anammox, despite these being critical environmental and safety concerns in nitrogen cycling systems.
Abstract and text state 'Complete NH4+ oxidation to N2 without accumulation of NO2− and NO3−' and 'NO and N2O were not detected' but detection limits and analytical methods are not specified. This is essential for validating the process as truly clean.
Versuch. Use gas chromatography with electron capture detection (GC-ECD) or cavity ring-down spectroscopy (CRDS) to quantify N2O and NO at detection limits <1 ppm; run 7-day continuous operation at 0.6 V vs. SHE.
Mittel No investigation of pH effects on EET-dependent anammox, despite pH being critical for both anammox metabolism and electrode kinetics.
All experiments appear to be conducted at unspecified pH; text mentions 'OH− ions generated from water' but no pH control or variation is reported. Anammox typically requires pH 6.5–8.5; electrode potential is pH-dependent.
Versuch. Operate MECs at pH 6.5, 7.0, 7.5, 8.0, 8.5 with 0.6 V vs. SHE applied; measure current density, NH4+ removal rate, and biofilm composition (FISH) at each pH.
Mittel No long-term stability data (>200 days) for electrode-dependent anammox biofilms, limiting assessment of practical applicability.
Longest experiment shown is ~144 hours (6 days) in Fig. 3a; Fig. 2a shows ~50 days but with multiple operational changes (NO2− addition/removal). Biofilm fouling, electrode degradation, and microbial drift are not addressed.
Versuch. Operate single MEC at constant 0.6 V vs. SHE with continuous NH4+ feed for 180 days; measure current density, NH4+ removal, biofilm thickness (SEM), and community composition (16S rRNA) monthly.
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Was gemacht wurde
- Systemtyp
- MEC
Was funktioniert hat
Zusammenfassung
Anaerobic ammonium oxidation (anammox) bacteria contribute significantly to the global nitrogen cycle and play a major role in sustainable wastewater treatment. Anammox bacteria convert ammonium (NH 4 + ) to dinitrogen gas (N 2 ) using intracellular electron acceptors such as nitrite (NO 2 - ) or nitric oxide (NO). However, it is still unknown whether anammox bacteria have extracellular electron transfer (EET) capability with transfer of electrons to insoluble extracellular electron acceptors. Here we show that freshwater and marine anammox bacteria couple the oxidation of NH 4 + with transfer of electrons to insoluble extracellular electron acceptors such as graphene oxide or electrodes in microbial electrolysis cells. 15 N-labeling experiments revealed that NH 4 + was oxidized to N 2 via hydroxylamine (NH 2 OH) as intermediate, and comparative transcriptomics analysis revealed an alternative pathway for NH 4 + oxidation with electrode as electron acceptor. Complete NH 4 + oxidation to N 2 without accumulation of NO 2 - and NO 3 - was achieved in EET-dependent anammox. These findings are promising in the context of implementing EET-dependent anammox process for energy-efficient treatment of nitrogen.
Schlagwörter
Kennungen
- PubMed
- 32345973
- Zeitschrift
- Nature Communications
- Jahr
- 2020
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