Addition Of Electron Donors Research Articles

A facile and fast strategy for cathodic electroactive-biofilm assembly via magnetic nanoparticle bioconjugation

Microbial electrosynthesis is a promising electricity-driven technology for converting carbon dioxide into value-added compounds, but the formation of cathodic electroactive-biofilms (CEBs) is challenging. Herein, we have demonstrated an innovative strategy for CEBs assembly via magnetic nanoparticle bioconjugation, which lies in the synergistic interactions among a bonder (Streptavidin, SA), conductive nanomaterials (Fe3O4), and a methanogen (M. barkeri). The results showed that the bioconjugated M. barkeri-SA-Fe3O4 biohybrids significantly enhanced both methane yield (33.2-fold) and faradaic efficiency (5.6-fold), compared with that of bare M. barkeri. Such an enhancement was attributed to the improved viability of CEBs with a higher biomass density. Particularly, more live cells were presented in the inner biofilms and promoted the long-distance electron exchange between the live outer-layer biofilm and the cathode electrode. Meanwhile, the higher redox activity of CEBs with the M. barkeri-SA-Fe3O4 biohybrids resulted in an improved transient charge storage capability, which was beneficial for the biological CO2-to-CH4 conversion via acting as an additional electron donor. This work has provided a new approach to accelerate the formation of CEBs and subsequent electron transfer, which holds a great potential for accomplishing electrosynthesis and CO2 fixation.

Computational Design of Novel Allosteric Inhibitors for Plasmodium falciparum DegP.

The serine protease, DegP exhibits proteolytic and chaperone activities, essential for cellular protein quality control and normal cell development in eukaryotes. The P. falciparum DegP is essential for the parasite survival and required to combat the oscillating thermal stress conditions during the infection, protein quality checks and protein homeostasis in the extra-cytoplasmic compartments, thereby establishing it as a potential target for drug development against malaria. Previous studies have shown that diisopropyl fluorophosphate (DFP) and the peptide SPMFKGV inhibit E. coli DegP protease activity. To identify novel potential inhibitors specific to PfDegP allosteric and the catalytic binding sites, we performed a high throughput in silico screening using Malaria Box, Pathogen Box, Maybridge library, ChEMBL library and the library of FDA approved compounds. The screening helped identify five best binders that showed high affinity to PfDegP allosteric (T0873, T2823, T2801, RJC02337, CD00811) and the catalytic binding site (T0078L, T1524, T2328, BTB11534 and 552691). Further, molecular dynamics simulation analysis revealed RJC02337, BTB11534 as the best hits forming a stable complex. WaterMap and electrostatic complementarity were used to evaluate the novel bio-isosteric chemotypes of RJC02337, that led to the identification of 231 chemotypes that exhibited better binding affinity. Further analysis of the top 5 chemotypes, based on better binding affinity, revealed that the addition of electron donors like nitrogen and sulphur to the side chains of butanoate group are more favoured than the backbone of butanoate group. In a nutshell, the present study helps identify novel, potent and Plasmodium specific inhibitors, using high throughput in silico screening and bio-isosteric replacement, which may be experimentally validated.

Electrochemical enrichment of marine denitrifying bacteria to enhance nitrate metabolization in seawater

High concentrations of nitrate from industrial discharges to coastal marine environments are a matter of concern owing to their ecological consequences. In the last years, Bioelectrochemical Denitrification Systems (BEDS) have emerged as a promising nitrate removal technology. However, they still have limitations, such as the enrichment strategy for specific microbial communities in the electrodes under natural conditions. In this study, three-electrode electrochemical cells were used to test microbial enrichment from natural seawater by applying three reported potentials associated with the dissimilatory denitrification process (−130, −260, and −570 mV vs. Ag/AgCl). The microbial community analysis showed that by applying −260 mV (vs. Ag/AgCl) to the working electrode, it was possible to significantly enrich denitrifying microorganisms, specifically Marinobacter, in comparison with the control. Furthermore, −260 mV (vs. Ag/AgCl) led to a significantly higher nitrate removal than other conditions, which, combined with cyclic voltammetry analysis, suggested that the polarized electrodes worked as external electron donors for nitrate reduction. Hence, this work demonstrates for the first time that it is possible to enrich marine denitrifying microorganisms by applying an overpotential of −260 mV (vs. Ag/AgCl) without the need for a culture medium, the addition of an exogenous electron donor (i.e., organic matter) or a previously enriched inoculum.

Actinonin resistance of pathogenic Vibrio anguillarum in aquaculture

Drug-resistant bacteria are an increasingly serious threat to the aquaculture industry. In order to develop new methods to combat these bacteria, it is necessary to first understand their mechanisms of drug resistance. We previously isolated a potential probiotic strain, Streptomyces sp. NHF165, which produced cytotoxic actinonin against the aquaculture pathogen Vibrio anguillarum. In this study, a spontaneous V. anguillarum mutant with an eight-fold increased MIC for actinonin was characterized for elucidation of actinonin resistance mechanisms. Transcriptomic analysis revealed significant up-regulation of genes related to anaerobic respiratory (nap and tor) and down-regulation of genes involved in anaerobic respiration (nqr, sdh and frd) in mutant strains. Meanwhile, no mutations in bacterial respiration genes or translation initiation genes (the proposed actinonin targeted pathway) were detected by whole genome resequencing analysis. A series of experiments confirmed that actinonin-resistance in the mutant strain was associated with respiration. When aerobic respiration was chemically disrupted by CCCP, the growth of wild-type V. anguillarum changed significantly, with a 11.74-fold increase in cell density under actinonin treatment. For anaerobic respiration, an increased nitrate reductase activity was detected in mutant cells by addition of an exogenous electron donor. Noteworthy was the finding that nitrate inhibited the growth of the wild-type strain but promoted the growth of the mutant. Futhermore, the product of nitrate-dependent anaerobic respiration, nitrite, did not arrest the growth of mutant V. anguillarum, which was contrary to previous reports and might exacerbate the formation of vibriosis. Finally, we showed that chemical inhibition of nitrate reductase could restore the susceptibility of mutant V. anguillarum to actinonin. Together these data demonstrate that the combined use of an anaerobic-respiratory inhibitor and an antibiotic might be a promising approach for the treatment of drug-resistant bacteria in aquaculture.

Cyclic Conversions in the Nitrogen Cycle.

The cyclic nature of specific conversions in the nitrogen cycle imposes strict limitations to the conversions observed in nature and explains for example why anaerobic ammonium oxidation (anammox) bacteria can only use nitrite – and not nitrate – as electron acceptor in catabolism, and why nitrite is required as additional electron donor for inorganic carbon fixation in anabolism. Furthermore, the biochemistry involved in nitrite-dependent anaerobic methane oxidation excludes the feasibility of using nitrate as electron acceptor. Based on the cyclic nature of these nitrogen conversions, we propose two scenarios that may explain the ecological role of recently discovered complete ammonia-oxidizing (comammox) Nitrospira spp., some of which were initially found in a strongly oxygen limited environment: (i) comammox Nitrospira spp. may actually catalyze an anammox-like metabolism using a biochemistry similar to intra-oxic nitrite-dependent methane oxidation, or (ii) scavenge all available oxygen for ammonia activation and use nitrate as terminal electron acceptor. Both scenarios require the presence of the biochemical machinery for ammonia oxidation to nitrate, potentially explaining a specific ecological niche for the occurrence of comammox bacteria in nature.

A staged representation electrochemical stimulated strategy to regulate intracellular reducing power for improving succinate production by Escherichia coli AFP111.

Escherichia coli AFP111 was previously engineered for succinate production by eliminating byproducts of synthesis pathways. Still, the succinate yield is limited due to the insufficient NADH supplement, when fed with glucose. Microbial electrolysis cell (MEC) allows microorganisms to perform unbalanced fermentation by establishing polarized cathode interaction. In this study, a cathode electrode was used as an additional electron donor to improve succinate synthesis by E. coli AFP111. In MEC with -0.65V (vs. Ag/AgCl) poised on cathode electrode, 95.72% electrons were transferred into cells via neutral red (NR), and the ratio of NADH/NAD+ increased by 2.5-fold. Meanwhile, compared with the control experiment, the value of oxidation-reduction potential (ORP) changed from -240 to -265mV in MEC, which was beneficial for NADH generation. During two-stage fermentation (no potential growth stage followed by electric stimulation) in MEC, succinate yield was increased by 29.09% (the final yield was 0.71g g-1 ), and glucose consumption rate was enhanced by 36.22%. In addition, the carbon flux was pumped to succinate and pyruvate metabolism was enhanced. Staged representation of electrochemical stimulated strategy is effective for succinate producing in engineered E. coli by regulating intracellular reducing power, which provides a new concept for producing reduced metabolite in unbalanced fermentation.

Sulfur autotrophic denitrification filter and heterotrophic denitrification filter: Comparison on denitrification performance, hydrodynamic characteristics and operating cost

Sulfur autotrophic denitrification (SAD) process, as an alternative to heterotrophic denitrification (HD) filter, receives growing interest in polishing the effluent from secondary sewage treatment. Although individual studies have indicated several advantages of SAD over HD, rare study has compared these two systems under identical condition and by using real secondary effluent. In this study, two small pilot scale filters (SAD and HD) were designed with identical configuration and operated parallelly by feeding the real secondary effluent from a WWTP. The results showed SAD filter can be started up without the addition of soluble electron donor, although the time (14 days) was about 3 times longer than that of HD filter. The nitrate removal rate of SAD filter at HRT of 1.4 h was measured as 0.268 ± 0.047 kg N/(m3∙d). Similar value was observed in HD filter with supplementing 90 mg/L COD. The COD concentration of effluent always kept lower than that of influent in SAD filter but not in HD filter. In addition, SAD filter could maintain a stable denitrification performance without backwash for 15 days, while decline of nitrate removal rate was observed in HD filter just 2 days after stopping the backwash. This different behavior was further confirmed as the SAD filter had a better hydraulic flow pattern. Analysis according to high-throughput 16S rRNA gene-based Illumina MiSeq sequencing clearly showed the microbial community evolution and differentiation among the samples of seed sludge, SAD and HD filters. Finally, the economic assessment was carried out, showing the operation cost of SAD filter was over 50% lower than that of HD filter.

Direct Conversion of Food Waste Extract into Caproate: Metagenomics Assessment of Chain Elongation Process.

In a circular economy strategy, waste resources can be used for the biological production of high added-value substances, such as medium chain fatty acids (MCFAs), thus minimising waste and favouring a sustainable process. This study investigates single-stage fermentation processes for the production of MCFAs in a semi-continuous reactor treating the extract of real food waste (FW), without the addition of external electron donors. Two sequential acidogenic fermentation tests were carried out at an organic loading rate (OLR) of 5 and 15 gCOD L−1d−1 with a hydraulic retention time of 4 days and pH controlled at 6 ± 0.2. The highest level of caproate (4.8 g L−1) was observed at OLR of 15 gCOD L−1d−1 with a microbiome mainly composed by lactate-producing Actinomyces, Atopobium, and Olsenella species and caproate-producing Pseudoramibacter. Metagenomic analysis revealed the presence of key enzymes for the production of lactate, such as lactate dehydrogenase and pyruvate ferredoxin oxidoreductase, as well as several enzymes involved in the reverse β-oxidation pathway, thus suggesting the occurrence of a lactate-based chain elongation process.

Effect of reactor operating conditions on carboxylate production and chain elongation from co-fermented sludge and food waste

Abstract Nowadays, fermentation of organic wastes for the production of carboxylic acids as precursors of higher-value products has attracted significant attention. In this paper, sewage sludge and food waste were co-fermented to produce carboxylic acids and study the subsequent chain elongation process. The Copenhagen waste stream scenario was taken as a case study. Firstly, design of experiments was used to investigate the overall carboxylic acids and hexanoic acid production in batch, as a function of the co-fermentation ratio, substrate to co-culture ratio and initial pH. Optimal operating conditions for hexanoic acid were obtained with SS/FW 6.61, S/Xo 6.73 and initial pH 6.83. Statistical optimization increased the overall carboxylic acid titer by 41%, while co-fermentation allowed to increase hexanoate annual production up to 77%. Furthermore, a continuous fermentation experiment was performed to study the effect of reactor operating conditions. The overall carboxylates titer was 2 times higher, which also favored chain elongation compared to batch mode. An increasing loading rate did not affect the overall carboxylate titer, however the hexanoic acid titer increased by 44%. A maximum titer of 4.9 g/l of hexanoic acid was produced, achieving a productivity of 2.46 g/l/d of hexanoic acid with a retention time of 2 d and no external electron donor addition. This would correspond to 610 t/y of hexanoic acid and 350 t/y of other carboxylic acids that could be produced, based on the waste availability in Copenhagen.

Construction of self-enhanced photoelectrochemical platform for L-cysteine detection via electron donor-acceptor type coumarin 545 aggregates.

Self-enhanced electron donor-acceptor type coumarin 545 aggregates prepared via an anionic surfactant-assisted reprecipitation method provide an underlying approach for the photoelectrochemical detection of L-cysteine, which can be employed in aqueous solution without the addition of electron donors.

Влияние различных типов электронодонорных добавок и условий полимеризации на температуру стеклования растворных бутадиен-стирольных каучуков

Влияние различных типов электронодонорных добавок и условий полимеризации на температуру стеклования растворных бутадиен-стирольных каучуков

A sustainable way to reuse Cr(VI) into an efficient biological nanometer electrocatalyst by Bacillus megaterium

The remediation of heavy metal is facing the great challenge of failing to achieve valuable transformation. Therefore, the development of a sustainable technology for heavy metal recycling and reuse is essential. The present study proposed a new way to convert Cr(VI) into value-added biological Cr2O3 nanoparticles (bio-Cr2O3 NPs) with B. megaterium-secreted tryptophan residues proteins (TPN). In this process, Cr(VI) was reduced extracellularly to Cr(III) by B. megaterium without additional reductant and electron donors. This study overcomes the difficulty of separation of NPs and biomass, and realizes the recovery of bio-Cr2O3 NPS from biomass. The conversing efficiency of bio-Cr2O3 NPs reached the highest level (96.56%) at the concentration of 10 ppm Cr(VI). In particular, bio-Cr2O3 NPs exhibited excellent catalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, outperforming chemically synthesized Cr-base catalysts. Three-dimensional matrix fluorescence (EEM), verification of tryptophan reduction and computation chemistry fully confirmed that TPN was responsible for the bio-Cr2O3 NPs formation. This comprehensive approach to bioremediation, synthesis NPs and recovery, as well as application will open a window for sustainable energy development and heavy metal pollution remediation.

Surface modification of TiO2 with Pd nanoparticles for enhanced photocatalytic oxidation of benzene micropollutants

This paper describes a simple method for the modification of TiO2 surface with palladium to prepare a highly active photocatalyst for oxidation of benzene micropollutants in air. The method consists of the impregnation of anatase TiO2 with a solution of palladium (II) acetate (Pd(OAc)2) in acetone followed by photodecomposition of Pd(OAc)2 under UV irradiation. No additional electron donor is required for Pd photodeposition because acetate ligands play this role. Photodecomposition of Pd(OAc)2 can be efficiently performed either before the target photocatalytic reaction or in situ during the reaction. Pd-loaded photocatalysts were characterized using UV–vis DRS, XPS, TEM, EDX, and CO chemisorption techniques. The formation of metallic (Pd0) and oxidized (PdOx) palladium on the TiO2 surface was shown. An increased amount of metallic Pd was observed during photodecomposition of Pd(OAc)2 compared to its thermal decomposition at low temperature. The modification of TiO2 with Pd nanoparticles substantially increased its photocatalytic activity in the oxidation of benzene vapor under UV light. A Pd content of 1 wt.% was found to be optimum, which provided a three-fold increase in activity compared to pristine TiO2. In addition to increasing the oxidation rate, Pd nanoparticles suppressed the formation of CO as a byproduct during the process that increased the efficiency of air purification by the photocatalytic oxidation method. The proposed preparation techniques can be employed for easy modification of powdered photocatalysts or fabric filters used in photocatalytic air purifiers.

The effect of the polarised cathode, formate and ethanol on chain elongation of acetate in microbial electrosynthesis

Reduction of CO2 to acetate in microbial electrosynthesis has been widely studied. However, the selective and quantitative production of longer chain chemicals and biofuels is still a bottleneck. Lack of sufficient energy provided by only the cathode electrode in Bio-electrochemical systems during chain elongation is one of the key challenges. It is assumed that additional electron donors than a polarised cathode is required to steer the production towards longer chain of carboxylates than acetate. In this study, formate and ethanol were supplied separately in the reactors fed by CO2 for 45 days in addition to the cathodes poised at −1.0 V vs. Ag/AgCl to investigate their effect on production. Although acetate was still the major product, supplying electron donors directed the production towards more diverse and longer chain organic chemicals than that in presence of the polarised cathode only. Significant improvement in the production of butyrate (×3.8 increase in maximum concentration) and butanol (maximum of 6.8 ± 0.3 mmol C L−1) was observed after supplying formate, while ethanol increased the diversity of the products. Supplying formate and ethanol in reactors for another 30 days under open circuit potential clarified that only ethanol could provide sufficient energy for butyrate production from acetate in the absence of polarised cathode, which reached the highest butyrate concentration of 19.1 ± 2.3 mmol C L−1. Formate was only consumed in presence of polarised cathode. It is proposed in our study that production of C4 products in presence of only cathodic electrode or cathodic electrode and formate could be associated to initial reduction of acetate to ethanol, consumed for production of C4 products through acetate. Trace levels of caproate and hexanol were detected in both reactors supplied with formate and ethanol only in the presence of polarised cathode.

Enhanced low-temperature denitrification by microbial consortium using solid-phase humin

Reducing the use of liquid organic carbon electron donors during biostimulation of heterotrophic denitrification is critical for sustainable groundwater remediation. Solid-phase humin isolated from natural sources can provide a cost-effective alternative to classical electron donors. In this study, the low-temperature denitrification capacity of an acetate-fed microbial community was enhanced using humin at 20 °C and 10 °C. These enhancements were not caused by faster acetate consumption and greater bacterial growth with the addition of humin. Estimation of the electron balance and first-order kinetics suggested that the enhancement in denitrification occurred mainly after acetate exhaustion. Humin may therefore have acted as an additional electron donor for the denitrifying microbial community, with the reduced quinone group in humin potentially responsible for electron donation. The addition of humin increased the richness and diversity of the denitrifying microbial community, in which Dechloromonas spp. played a critical role. Given the prevalence of humin and denitrifiers using humic substances, our results have important implications in the bioremediation of nitrate-contaminated groundwater using less liquid organic carbon electron donors.

Separation of Biological Events from the Photoanode: Toward the Ferricyanide-Mediated Redox Cyclic Photoelectrochemical System of an Integrated Photoanode and Photocathode.

Photoanode sensing platforms with remarkable photoelectrochemical (PEC) response and satisfying visible-light absorption have become the most promising detection systems. Nevertheless, their inevitable electrophilic character limits their expansion in the bioassay because of reductive substances in serum or other body fluids that can severely interfere with the photocurrent to be read. To solve it, a PEC platform-assembled dual-active electrode is designed to realize the separation of biological monitoring from the photoanode. The ferricyanide ([Fe(CN)6]3-)-mediated redox cycle is first proposed to meet the gain and loss electron requirements of the PEC system. It can avoid the self-reaction in the electrolyte caused by the addition of a traditional electron donor and acceptor, for instance, ascorbic acid and hydrogen peroxide. As a consequence, the traditional counter electrode (Pt wire) is replaced by Fe2O3/AgInS2 heterojunction, which can amplify the PEC response of the cathode to meet the requirement of trace analysis. An aptasensor fabricated by the above strategies exhibits convincing data for 17β-estradiol (E2) detection from which a wide detection range is obtained in 10 fg/mL to 1 μg/mL with a detection limit of 2.74 fg/mL (S/N = 3). These advanced elements show a rosy prospect for environmental monitoring and point-of-care biomarker diagnosis.

A kinetic study on carboxylic acids production using bovine slaughterhouse wastewater: a promising substrate for resource recovery in biotechnological processes.

Carboxylic acids (CA) are considered high added-value compounds, and their production from wastes has gained economic and environmental notoriety. However, the CA production and kinetic modeling using some agro-industrial wastewaters, such as bovine slaughterhouse wastewater (SHW), are not well reported in the literature. Therefore, the objective of this work was to evaluate the CA production potential using SHW as a substrate under acidogenic conditions and to apply mathematical models to estimate the kinetic parameters of particulate organic matter hydrolysis, soluble organic matter consumption, and CA production. Tests were carried out in quadruplicate batch reactors with a 250-mL reaction volume, with brewery sludge as inoculum and using chloroform (0.05%, v/v) for methanogenesis inhibition. The obtained yield was 0.55g acids gCODA-1, corresponding to 0.76 gCOD gCODA-1. The production of caproic acid without the addition of electron donors was achieved. Mathematical models that describe exponential growth, such as the first-order exponential model, cone model, and Fitzhugh model, were the most suitable to describe the production kinetics of CA. Finally, SHW seems to be a promising substrate to be investigated in the carboxylic platform.

Enhancement of cell growth by uncoupling extracellular electron uptake and oxidative stress production in sediment sulfate-reducing bacteria

Microbial extracellular electron uptake (EEU) from solid electron donors has critical implications for microbial energy acquisition in energy-limited environments as well as electrochemical microbial technologies. Although EEU supplies sufficient energy to support cellular growth, additional soluble electron donors are required for most microbes to grow on electrode surfaces. Here, we demonstrated that the minimization of exogenous and endogenous oxidative stress greatly enhanced the growth rate of the sediment EEU-capable sulfate-reducing bacterium Desulfovibrio ferrophilus IS5 on an electrode without the addition of a soluble electron donor. Single-cell activity analysis by nanoscale secondary ion mass spectrometry showed that the metabolic activity of IS5 cells on the electrode was significantly enhanced following incubation in an H-type reactor, which was configured to reduce the exposure of cells to the potential oxidative stress source of the Pt counter electrode (CE). Additionally, the highest metabolic activity was observed at an electrode potential of −0.4 V (versus the standard hydrogen electrode), where electron uptake rate was not at peak. Compared to a single-chamber reactor, incubation in an H-type reactor at −0.4 V shortened the cell doubling time by 50-fold, which resulted in sufficient anabolism for cell replication (15N/Ntotal > 50%). The production of strongly oxidizing species at the CE was confirmed by X-ray photoelectron spectroscopy and inductively coupled plasma mass spectrometry analyses. Transcriptome analysis revealed overexpression of antioxidative genes in cells incubated at a potential with higher current production. These results suggested that higher levels of endogenous oxidative species were produced by a more reduced electron-transport chain from trace amounts of oxygen in the reactor, thereby lowering cell activity. In conclusion, EEU may enable sediment microbes to undergo enhanced cell growth and to find niches on minerals under anaerobic energy-limited conditions, where oxidative stress is much less likely to be present.

Stimuli‐Responsive Resorcin[4]arene Cavitands: Toward Visible‐Light‐Activated Molecular Grippers

Resorcin[4]arene cavitands, equipped with diverse quinone (Q) and [Ru(bpy)2 dppz]2+ (bpy=2,2'-bipyridine, dppz=dipyrido[3,2-a:2',3'-c]phenazine) photosensitizing walls in different configurations, were synthesized. Upon visible-light irradiation at 420 nm, electron transfer from the [Ru(bpy)2 dppz]2+ to the Q generates the semiquinone (SQ) radical anion, triggering a large conformational switching from a flat kite to a vase with a cavity for the encapsulation of small guests, such as cyclohexane and heteroalicyclic derivatives, in CD3 CN. Depending on the molecular design, the SQ radical anion can live for several minutes (≈10 min) and the vase can be generated in a secondary process without need for addition of a sacrificial electron donor to accumulate the SQ state. Switching can also be triggered by other stimuli, such as changes in solvent, host-guest complexation, and chemical and electrochemical processes. This comprehensive investigation benefits the development of stimuli-responsive nanodevices, such as light-activated molecular grippers.

Remediation of nitrogen polluted water using Fe–C microelectrolysis and biofiltration under mixotrophic conditions

A hybrid biofilter was established on Fe–C supported carriers aimed to enhance nitrogen removal from polluted water of low Carbon/Nitrogen (C/N) ratio. Effects of organic loadings, hydraulic retention time (HRT), additional electron donor (Fe2+) supplementation and operation mode on the performance of the biofilter were investigated. Results showed that up-flow operation mode was better than down-flow mode in terms of nitrate and total nitrogen (TN) removal at low COD/N. The average removal of NO3−-N, NH4+ –N and TN attained 83.1%, 84.7% and 81.2%, respectively, under the conditions of influent COD/NO3−-N = 1.5–3.6, HRT = 10 h and up-flow operation. When the biofilter was operated under autotrophic conditions without organic compounds in influent as electron donors, the biofilter achieved a NO3−-N removal of 46% and TN removal of 56% depending on the innate electron donors provided by the Fe–C carriers. Supplementation of Fe2+ in influent further promoted autotrophic denitrifying process, and the removal of NO3−-N and TN increased to 96.3% and 84.7%, respectively, at the mol ratio of Fe2+/NO3− = 10 and HRT = 10 h. The microbial community was analyzed for the biofilm samples enriched under heterotrophic and autotrophic conditions. The Fe–C biofilter boosted the growth of a large population of mixotrophic denitrifying bacteria including Gallionella, heterotrophic denitrifying bacteria Denitratisoma, and autotrophic denitrifying bacteria Thiobacillus and Thioalkalispira. On the whole, the biofilter coupled with Fe–C micro-electrolysis provides a novel strategy to treat polluted water of low C/N under both heterotrophic and autotrophic conditions.