Cobalt Resistance via Detoxification and Mineralization in the Iron-Reducing Bacterium Geobacter sulfurreducens

Elucidating the impacts of cobalt (II) ions on extracellular electron transfer and pollutant degradation by anodic biofilms in bioelectrochemical systems during industrial wastewater treatment

Electrogenic biofilms in bioelectrochemical systems (BES) are critical in wastewater treatment. Industrial effluents often contain cobalt (Co2+); however, its impact on biofilms is unknown. This study investigated how increasing Co2+ concentrations (0-30 mg/L) affect BES biofilm community dynamics, extracellular polymeric substances, microbial metabolism, electron transfer gene expression, and electrochemical performance. The research revealed that as Co2+ concentrations increased, power generation progressively declined, from 345.43 ± 4.07 mW/m2 at 0 mg/L to 160.51 ± 0.86 mW/m2 at 30 mg/L Co2+. However, 5 mg/L Co2+ had less effect. The Co2+ removal efficiency in the reactors fed with 5 and 10 mg/L concentrations exceeded 99% and 94%, respectively. However, at 20 and 30 mg/L, the removal efficiency decreased substantially, likely because of reduced biofilm viability. FTIR indicated the participation of biofilm functional groups in Co2+ uptake. XPS revealed Co2+ presence in biofilms as CoO and Co(OH)2, indicating precipitation also aided removal. Cyclic voltammetry and electrochemical impedance spectroscopy tests revealed that 5 mg/L Co2+ had little impact on the electrocatalytic activity, while higher concentrations impaired it. Furthermore, at a concentration of 5 mg/L Co2+, there was an increase in the proportion of the genus Anaeromusa-Anaeroarcus, while the genus Geobacter declined at all tested Co2+ concentrations. Additionally, higher concentrations of Co2+ suppressed the expression of extracellular electron transfer genes but increased the expression of Co2+-resistance genes. Overall, this study establishes how Co2+ impacts electrogenic biofilm composition, function, and treatment efficacy, laying the groundwork for the optimized application of BES in remediating Co2+-contaminated wastewater.

Taxonomic Diversity and Functional Traits of Soil Bacterial Communities under Radioactive Contamination: A Review

Studies investigating the taxonomic diversity and structure of soil bacteria in areas with enhanced radioactive backgrounds have been ongoing for three decades. An analysis of data published from 1996 to 2024 reveals changes in the taxonomic structure of radioactively contaminated soils compared to the reference, showing that these changes are not exclusively dependent on contamination rates or pollutant compositions. High levels of radioactive exposure from external irradiation and a high radionuclide content lead to a decrease in the alpha diversity of soil bacterial communities, both in laboratory settings and environmental conditions. The effects of low or moderate exposure are not consistently pronounced or unidirectional. Functional differences among taxonomic groups that dominate in contaminated soil indicate a variety of adaptation strategies. Bacteria identified as multiple-stress tolerant; exhibiting tolerance to metals and antibiotics; producing antioxidant enzymes, low-molecular antioxidants, and radioprotectors; participating in redox reactions; and possessing thermophilic characteristics play a significant role. Changes in the taxonomic and functional structure, resulting from increased soil radionuclide content, are influenced by the combined effects of ionizing radiation, the chemical toxicity of radionuclides and co-contaminants, as well as the physical and chemical properties of the soil and the initial bacterial community composition. Currently, the quantification of the differential contributions of these factors based on the existing published studies presents a challenge.

An Overview of Bacteria-Mediated Heavy Metal Bioremediation Strategies

Contamination-free groundwater is considered a good source of potable water. Even in the twenty-first century, over 90 percent of the population is reliant on groundwater resources for their lives. Groundwater influences the economical state, industrial development, ecological system, and agricultural and global health conditions worldwide. However, different natural and artificial processes are gradually polluting groundwater and drinking water systems throughout the world. Toxic metalloids are one of the major sources that pollute the water system. In this review work, we have collected and analyzed information on metal-resistant bacteria along with their genetic information and remediation mechanisms of twenty different metal ions [arsenic (As), mercury (Hg), lead (Pb), chromium (Cr), iron (Fe), copper (Cu), cadmium (Cd), palladium (Pd), zinc (Zn), cobalt (Co), antimony (Sb), gold (Au), silver (Ag), platinum (Pt), selenium (Se), manganese (Mn), molybdenum (Mo), nickel (Ni), tungsten (W), and uranium (U)]. We have surveyed the scientific information available on bacteria-mediated bioremediation of various metals and presented the data with responsible genes and proteins that contribute to bioremediation, bioaccumulation, and biosorption mechanisms. Knowledge of the genes responsible and self-defense mechanisms of diverse metal-resistance bacteria would help us to engineer processes involving multi-metal-resistant bacteria that may reduce metal toxicity in the environment.

Exploring the role of microbial proteins in controlling environmental pollutants based on molecular simulation

Molecular simulation has been widely used to study microbial proteins' structural composition and dynamic properties, such as volatility, flexibility, and stability at the microscopic scale. Herein, this review describes the key elements of molecular docking and molecular dynamics (MD) simulations in molecular simulation; reviews the techniques combined with molecular simulation, such as crystallography, spectroscopy, molecular biology, and machine learning, to validate simulation results and bridge information gaps in the structure, microenvironmental changes, expression mechanisms, and intensity quantification; illustrates the application of molecular simulation, in characterizing the molecular mechanisms of interaction of microbial proteins with four different types of contaminants, namely heavy metals (HMs), pesticides, dyes and emerging contaminants (ECs). Finally, the review outlines the important role of molecular simulations in the study of microbial proteins for controlling environmental contamination and provides ideas for the application of molecular simulation in screening microbial proteins and incorporating targeted mutagenesis to obtain more effective contaminant control proteins.

Metabolism and gene sequence variation in Turicella otitidis implies its adaptability and pathogenicity in extra-otic infection: a systematic review

Turicella otitidis belongs to the Corynebacteriaceae family and is a normal inhabitant of the ear and exists in a commensal relationship with its host. In children, T. otitidis is frequently associated with otitis media. The emergence of Turicella otitidis as a pathogen is concerning, particularly due to the limited availability of data on its pathogenic properties. The objective of this study is to conduct a systematic review of T. otitidis infections occurring in both the ear and other anatomical sites, and to summarize the differences in metabolism and genome sequences between isolates obtained from the ear and blood.

Global transcriptional analysis of Geobacter sulfurreducens gsu1771 mutant biofilm grown on two different support structures

Electroactive biofilms formation by the metal-reducing bacterium Geobacter sulfurreducens is a step crucial for bioelectricity generation and bioremediation. The transcriptional regulator GSU1771 controls the expression of essential genes involved in electron transfer and biofilm formation in G. sulfurreducens, with GSU1771-deficient producing thicker and more electroactive biofilms. Here, RNA-seq analyses were conducted to compare the global gene expression patterns of wild-type and Δgsu1771 mutant biofilms grown on non-conductive (glass) and conductive (graphite electrode) materials. The Δgsu1771 biofilm grown on the glass surface exhibited 467 differentially expressed (DE) genes (167 upregulated and 300 downregulated) versus the wild-type biofilm. In contrast, the Δgsu1771 biofilm grown on the graphite electrode exhibited 119 DE genes (79 upregulated and 40 downregulated) versus the wild-type biofilm. Among these DE genes, 67 were also differentially expressed in the Δgsu1771 biofilm grown on glass (56 with the same regulation and 11 exhibiting counter-regulation). Among the upregulated genes in the Δgsu1771 biofilms, we identified potential target genes involved in exopolysaccharide synthesis (gsu1961-63, gsu1959, gsu1972-73, gsu1976-77). RT-qPCR analyses were then conducted to confirm the differential expression of a selection of genes of interest. DNA-protein binding assays demonstrated the direct binding of the GSU1771 regulator to the promoter region of pgcA, pulF, relA, and gsu3356. Furthermore, heme-staining and western blotting revealed an increase in c-type cytochromes including OmcS and OmcZ in Δgsu1771 biofilms. Collectively, our findings demonstrated that GSU1771 is a global regulator that controls extracellular electron transfer and exopolysaccharide synthesis in G. sulfurreducens, which is crucial for electroconductive biofilm development.

Retracted: The bidirectional extracellular electron transfer process aids iron cycling by Geoalkalibacter halelectricus in a highly saline-alkaline condition

Bidirectional extracellular electron transfer (EET) is crucial to upholding microbial metabolism with insoluble electron acceptors or donors in anoxic environments. Investigating bidirectional EET-capable microorganisms is desired to understand the cell-cell and microbe-mineral interactions and their role in mineral cycling besides leveraging their energy generation and conversion, biosensing, and bio-battery applications. Here, we report on iron cycling by haloalkaliphilic Geoalkalibacter halelectricus via bidirectional EET under haloalkaline conditions. It efficiently reduces Fe3+ oxide (Fe2O3) to Fe0 at a 0.75 ± 0.08 mM/mgprotein/d rate linked to acetate oxidation via outward EET and oxidizes Fe0 to Fe3+ at a 0.24 ± 0.03 mM/mgprotein/d rate via inward EET to reduce fumarate. Bioelectrochemical cultivation confirmed its outward and inward EET capabilities. It produced 895 ± 23 µA/cm2 current by linking acetate oxidation to anode reduction via outward EET and reduced fumarate by drawing electrons from the cathode (‒2.5 ± 0.3 µA/cm2) via inward EET. The cyclic voltammograms of G. halelectricus biofilms revealed redox moieties with different formal potentials, suggesting the involvement of different membrane components in bidirectional EET. The cyclic voltammetry and GC-MS analysis of the cell-free spent medium revealed the lack of soluble redox mediators, suggesting direct electron transfer by G. halelecctricus in achieving bidirectional EET. By reporting on the first haloalkaliphilic bacterium capable of oxidizing and reducing insoluble Fe0 and Fe3+ oxide, respectively, this study advances the limited understanding of the metabolic capabilities of extremophiles to respire on insoluble electron acceptors or donors via bidirectional EET and invokes the possible role of G. halelectricus in iron cycling in barely studied haloalkaline environments. IMPORTANCE Bidirectional extracellular electron transfer (EET) appears to be a key microbial metabolic process in anoxic environments that are depleted in soluble electron donor and acceptor molecules. Though it is an ecologically important and applied microbial phenomenon, it has been reported with a few microorganisms, mostly from nonextreme environments. Moreover, direct electron transfer-based bidirectional EET is studied for very few microorganisms with electrodes in engineered systems and barely with the natural insoluble electron acceptor and donor molecules in anoxic conditions. This study advances the understanding of extremophilic microbial taxa capable of bidirectional EET and its role in barely investigated Fe cycling in highly saline-alkaline environments. It also offers research opportunities for understanding the membrane components involved in the bidirectional EET of G. halelectricus. The high rate of Fe3+ oxide reduction activity by G. halelectricus suggests its possible use as a biocatalyst in the anaerobic iron bioleaching process under neutral-alkaline pH conditions.

Purification and Characterization of a DegP-Type Protease from the Marine Bacterium Cobetia amphilecti KMM 296

A new member of the DegP-type periplasmic serine endoproteases of the S1C family from the marine bacterium Cobetia amphilecti KMM 296 (CamSP) was expressed in Escherichia coli cells. The calculated molecular weight, number of amino acids, and isoelectric point (pI) of the mature protein CamSP are 69.957 kDa, 666, and 4.84, respectively. The proteolytic activity of the purified recombinant protease CamSP was 2369.4 and 1550.9 U/mg with the use of 1% bovine serum albumin (BSA) and casein as the substrates, respectively. The enzyme CamSP exhibited maximum activity at pH 6.0-6.2, while it was stable over a wide pH range from 5.8 to 8.5. The optimal temperature for the CamSP protease activity was 50 °C. The enzyme required NaCl or KCl at concentrations of 0.3 and 0.5 M, respectively, for its maximum activity. The Michaelis constant (K_m) and V_max for BSA were determined to be 41.7 µg/mL and 0.036 µg/mL min^-1, respectively. The metal ions Zn²⁺, Cu²⁺, Mn²⁺, Li²⁺, Mg²⁺, and Ca²⁺ slightly activated CamSP, while the addition of CoCl₂ to the incubation mixture resulted in a twofold increase in its protease activity. Ethanol, isopropanol, glycerol, and Triton-X-100 increased the activity of CamSP from two- to four-times. The protease CamSP effectively degraded the wheat flour proteins but had no proteolytic activity towards soybean, corn, and the synthetic substrates, α-benzoyl-Arg-p-nitroanilide (BAPNA) and N-Succinyl-L-alanyl-L-alanyl-L-prolyl-L-phenylalanine 4-nitroanilide (SAPNA).

Microbial community composition and degradation potential of petroleum-contaminated sites under heavy metal stress

Total petroleum hydrocarbons (n-alkanes), semi-volatile organic compounds, and heavy metals pose major ecological risks at petrochemical-contaminated sites. The efficiency of natural remediation in situ is often unsatisfactory, particularly under heavy metal pollution stress. This study aimed to verify the hypothesis that after long-term contamination and restoration, microbial communities in situ exhibit significantly different biodegradation efficiencies under different concentrations of heavy metals. Moreover, they determine the appropriate microbial community to restore the contaminated soil. Therefore, we investigated the heavy metals in petroleum-contaminated soils and observed that heavy metals effects on distinct ecological clusters varied significantly. Finally, alterations in the native microbial community degradation ability were demonstrated through the occurrence of petroleum pollutant degradation function genes in different communities at the tested sites. Furthermore, structural equation modeling (SEM) was used to explain the influence of all factors on the degradation function of petroleum pollution. These results suggest that heavy metal contamination from petroleum-contaminated sites reduces the efficiency of natural remediation. In addition, it infers that MOD1 microorganisms have greater degradation potential under heavy metal stress. Utilizing appropriate microorganisms in situ may effectively help resist the stress of heavy metals and continuously degrade petroleum pollutants.

Metabolic turnover of cysteine-related thiol compounds at environmentally relevant concentrations by Geobacter sulfurreducens

Low-molecular-mass (LMM) thiol compounds are known to be important for many biological processes in various organisms but LMM thiols are understudied in anaerobic bacteria. In this work, we examined the production and turnover of nanomolar concentrations of LMM thiols with a chemical structure related to cysteine by the model iron-reducing bacterium Geobacter sulfurreducens. Our results show that G. sulfurreducens tightly controls the production, excretion and intracellular concentration of thiols depending on cellular growth state and external conditions. The production and cellular export of endogenous cysteine was coupled to the extracellular supply of Fe(II), suggesting that cysteine excretion may play a role in cellular trafficking to iron proteins. Addition of excess exogenous cysteine resulted in a rapid and extensive conversion of cysteine to penicillamine by the cells. Experiments with added isotopically labeled cysteine confirmed that penicillamine was formed by a dimethylation of the C-3 atom of cysteine and not via indirect metabolic responses to cysteine exposure. This is the first report of de novo metabolic synthesis of this compound. Penicillamine formation increased with external exposure to cysteine but the compound did not accumulate intracellularly, which may suggest that it is part of G. sulfurreducens' metabolic strategy to maintain cysteine homeostasis. Our findings highlight and expand on processes mediating homeostasis of cysteine-like LMM thiols in strict anaerobic bacteria. The formation of penicillamine is particularly noteworthy and this compound warrants more attention in microbial metabolism studies.

Selective bacterial separation of critical metals: towards a sustainable method for recycling lithium ion batteries

The large scale recycling of lithium ion batteries (LIBs) is essential to satisfy global demands for the raw materials required to implement this technology as part of a clean energy strategy. However, despite what is rapidly becoming a critical need, an efficient and sustainable recycling process for LIBs has yet to be developed. Biological reactions occur with great selectivity under mild conditions, offering new avenues for the implementation of more environmentally sustainable processes. Here, we demonstrate a sequential process employing two bacterial species to recover Mn, Co and Ni, from vehicular LIBs through the biosynthesis of metallic nanoparticles, whilst Li remains within the leachate. Moreover the feasibility of Mn recovery from polymetallic solutions was demonstrated at semi-pilot scale in a 30 L bioreactor. Additionally, to provide insight into the biological process occurring, we investigated selectivity between Co and Ni using proteomics to identify the biological response and confirm the potential of a bio-based method to separate these two essential metals. Our approach determines the principles and first steps of a practical bio-separation and recovery system, underlining the relevance of harnessing biological specificity for recycling and up-cycling critical materials.

Enhancement effects of dissolved organic matter leached from sewage sludge on microbial reduction and immobilization of Cr(VI) by Geobacter sulfurreducens

Sewage sludge has a high concentration of dissolved organic matter (DOM) which contains compounds that can serve as electron donors or shuttles for metal reduction by dissimilatory metal reducing bacteria (DMRB). In this study, Cr(VI) removal by G. sulfurreducens, a common DMRB present in anaerobic soils, was examined in the presence or absence of sludge DOM. Two different types of sludge DOM were tested; composted sludge DOM (C-DOM) and anaerobically digested sludge DOM (A-DOM). Both sludge DOMs enhanced Cr(VI) reduction by G. sulfurreducens, but C-DOM was more effective likely because it had higher concentrations of humic substances that served as electron shuttles. Transcriptomic studies indicated that G. sulfurreducens utilizes several different mechanisms to tolerate chromium including extracellular Cr(VI) reduction and immobilization by outer membrane c-type cytochromes and electrically conductive pili, intracellular Cr(VI) reduction by triheme cytochromes and NAD(P)H FMN reductase proteins, and chromium efflux by several P-type ATPase and RND transporter proteins. Microscopy experiments also showed that Cr(III) crystals formed on the surface of the cells, indicating that extracellular Cr(VI) reduction and adsorption was involved in the chromium removal process. These results help provide insight into the potential use of sewage sludge as an additive to enhance the bioremediation of chromium contaminated soils.

Extracellular proteins of Desulfovibrio vulgaris as adsorbents and redox shuttles promote biomineralization of antimony

Biomineralization is the key process governing the biogeochemical cycling of multivalent metals in the environment. Although some sulfate-reducing bacteria (SRB) are recently recognized to respire metal ions, the role of their extracellular proteins in the immobilization and redox transformation of antimony (Sb) remains elusive. Here, a model strain Desulfovibrio vulgaris Hildenborough (DvH) was used to study microbial extracellular proteins of functions and possible mechanisms in Sb(V) biomineralization. We found that the functional groups (N-H, CO, O-CO, NH₂-R and RCOH/RCNH₂) of extracellular proteins could adsorb and fix Sb(V) through electrostatic attraction and chelation. DvH could rapidly reduce Sb(V) adsorbed on the cell surface and form amorphous nanometer-sized stibnite and/or antimony trioxide, respectively with sulfur and oxygen. Proteomic analysis indicated that some extracellular proteins involved in electron transfer increased significantly (p < 0.05) at 1.8 mM Sb(V). The upregulated flavoproteins could serve as a redox shuttle to transfer electrons from c-type cytochrome networks to reduce Sb(V). Also, the upregulated extracellular proteins involved in sulfur reduction, amino acid transport and protein synthesis processes, and the downregulated flagellar proteins would contribute to a better adaption under 1.8 mM Sb(V). This study advances our understanding of how microbial extracellular proteins promote Sb biomineralization in DvH.

Influence of cobalt chloride and ferric citrate on purple non-sulfur bacteria Rhodopseudomonas yavorovii

Heavy metals that enter the environment due to natural processes or industrial activities, when accumulated, have a negative impact on organisms, including microorganisms. Microorganisms have developed various adaptations to heavy metal compounds. The aim of our work was to investigate the influence of ferric citrate and cobalt (II) chloride on biomass accumulation, indicators of free radical damage and activity of enzymes of the antioxidant defense system of bacteria Rhodopseudomonas yavorovii IMV B-7620, that were isolated from the water of Yavorivske Lake (Ukraine, Lviv region), which was formed as a result of flooding of a sulfur quarry. We used cultural, photometric methods, and statistical processing of the results was performed using two-way ANOVA and factor analysis. It was found that ferric citrate at a concentration of 1–12 mM causes inhibition of the accumulation of biomass of bacteria Rh. yavorovii IMV B-7620 up to 44.7%, and cobalt (II) chloride at a concentration of 1–15 mM – up to 70.4%, compared with the control. The studied concentrations of ferric citrate and cobalt (II) chloride cause free radical damage to lipids and proteins of Rh. yavorovii IMV B-7620. As a result of two-way ANOVA we found that under the influence of ferric citrate statistically significant changes in biomass accumulation, lipid hydroperoxides and thiobarbiturate reactive species content, superoxide dismutase activity were predetermined by increasing the concentration of metal salts as well as increasing the duration of cultivation of bacteria, while the content of diene conjugates and catalase activity changed with increasing duration of cultivation. Under the influence of cobalt (II) chloride, statistically significant changes in all studied indicators were found both due to the increase in the concentration of metal salts and with increasing duration of bacterial cultivation. The studied parameters of Rh. yavorovii IMV B-7620 cells under the influence of ferric citrate and cobalt (II) chloride are combined into two factors, that explain 95.4% and 99.2% of the total data variance, respectively. Under the influence of ferric citrate, the first latent factor included diene conjugates, thiobarbiturate reactive species, carbonyl groups in proteins, which are closely linked by a direct bond and inversely related to the content of lipid hydroperoxides and catalase activity. The second latent factor included duration of cultivation of bacteria, biomass accumulation, and superoxide dismutase activity, which are inversely related to lipid hydroperoxide content and catalase activity. Under the influence of cobalt (II) chloride, the first latent factor included the content of lipid hydroperoxides, carbonyl groups in proteins, as well as catalase and superoxide dismutase activities, which are inversely related to bacterial biomass.

Heterogeneous Structure Regulated by Selection Pressure on Bacterial Adhesion Optimized the Viability Stratification Structure of Electroactive Biofilms

As the core of microbial fuel cells (MFCs), the components and structure of electroactive biofilms (EABs) are essential for MFC performance. Bacterial adhesion plays a vital role in shaping the structure of EABs, but the effect of bacterial adhesion under selection pressure on EABs has not been systematically studied. Here, the response of the composition, structure, and electrochemical performance of EABs to the selective adhesion pressure due to the selective coordination of Fe(III) and Co(II) with thiol and the different affinities for bacteria on hybrid electrodes (Fe₁Co, Fe₄Co, and Fe₁₀Co) were comprehensively investigated. Compared with carbon cloth (CC), the appropriate selective adhesion pressure of Fe₄Co activated the dead inner core of EABs and optimized their viability stratification structure. Both the total viability and the viability of the inner core layer in the Fe₄Co EAB (0.67, 0.70 ± 0.01) were higher than those of the CC (0.46, 0.54 ± 0.01), Fe₁Co (0.50, 0.48 ± 0.03), and Fe₁₀Co (0.51, 0.51 ± 0.03). Moreover, a higher proportion of proteins was detected in the Fe₄Co EAB, enhancing the redox activity of extracellular polymeric substances. Fe₄Co enriched Geobacter and stimulated microbial metabolism. Electrochemical analysis revealed that the Fe₄Co EAB was the most electroactive EAB, with a maximum power density of 2032.4 mW m^-2, which was 1.7, 1.3, and 1.1 times that of the CC (1202.6 mW m^-2), Fe₁Co (1610.3 mW m^-2), and Fe₁₀Co (1824.4 mW m^-2) EABs, respectively. Our findings confirmed that highly active EABs could be formed by imposing selection pressure on bacterial adhesion.

Mechanisms underlying Clostridium pasteurianum's metabolic shift when grown with Geobacter sulfurreducens

Recently, a study showed that glycerol fermentation by Clostridium pasteurianum could be metabolically redirected when the electroactive bacterium Geobacter sulfurreducens was added in the culture. It was assumed that this metabolic shift of the fermentative species resulted from an interspecies electron transfer. The aim of this study was to find out the mechanisms used for this interaction and how they affect the metabolism of C. pasteurianum. To get insights into the mechanisms involved, several coculture setups and RNA sequencing with differential expression analysis were performed. As a result, a putative interaction model was proposed: G. sulfurreducens produces cobamide molecules that possibly modify C. pasteurianum metabolic pathway at the key enzyme glycerol dehydratase, and affect its vanadium nitrogenase expression. In addition, the results suggested that G. sulfurreducens' electrons could enter C. pasteurianum through its transmembrane flavin-bound polyferredoxin and cellular cytochrome b5-rubredoxin interplay, putatively reinforcing the metabolic shift. Unravelling the mechanisms behind the interaction between fermentative and electroactive bacteria helps to better understand the role of bacterial interactions in fermentation setups. KEY POINTS: • C. pasteurianum-G. sulfurreducens interaction inducing a metabolic shift is mediated • C. pasteurianum's metabolic shift in coculture might be induced by cobamides • Electrons possibly enter C. pasteurianum through a multiflavin polyferredoxin.

Competitive advantage of oxygen-tolerant bioanodes of Geobacter sulfurreducens in bioelectrochemical systems

Oxidative stress greatly limits current harvesting from anode biofilms in bioelectrochemical systems yet insufficient knowledge of the antioxidant responses of electricigens prevents optimization. Using Geobacter sulfurreducens PCA as a model electricigen, we demonstrated enhanced oxygen tolerance and reduced electron losses as the biofilms grew in height on the anode. To investigate the molecular basis of biofilm tolerance, we developed a genetic screening and isolated 11 oxygen-tolerant (oxt) strains from a library of transposon-insertion mutants. The aggregative properties of the oxt mutants promoted biofilm formation and oxygen tolerance. Yet, unlike the wild type, none of the mutants diverted respiratory electrons to oxygen. Most of the oxt mutations inactivated pathways for the detoxification of reactive oxygen species that could have triggered compensatory chronic responses to oxidative stress and inhibit aerobic respiration. One of the mutants (oxt10) also had a growth advantage with Fe(III) oxides and during the colonization of the anode electrode. The enhanced antioxidant response in this mutant reduced the system's start-up and promoted current harvesting from bioanodes even in the presence of oxygen. These results highlight a hitherto unknown role of oxidative stress responses in the stability and performance of current-harvesting biofilms of G. sulfurreducens and identify biological and engineering approaches to grow electroactive biofilms with the resilience needed for practical applications.