A PadR family transcriptional repressor regulates the transcription of chromate efflux transporter in Enterobacter sp. Z1.

Chromium is a prevalent toxic heavy metal, and chromate [Cr(VI)] exhibits high mutagenicity and carcinogenicity. The presence of the Cr(VI) efflux protein ChrA has been identified in strains exhibiting resistance to Cr(VI). Nevertheless, certain strains of bacteria that are resistant to Cr(VI) lack the presence of ChrB, a known regulatory factor. Here, a PadR family transcriptional repressor, ChrN, has been identified as a regulator in the response of Enterobacter sp. Z1(CCTCC NO: M 2019147) to Cr(VI). The chrN gene is cotranscribed with the chrA gene, and the transcriptional expression of this operon is induced by Cr(VI). The binding capacity of the ChrN protein to Cr(VI) was demonstrated by both the tryptophan fluorescence assay and Ni-NTA purification assay. The interaction between ChrN and the chrAN operon promoter was validated by reporter gene assay and electrophoretic mobility shift assay. Mutation of the conserved histidine residues His14 and His50 resulted in loss of ChrN binding with the promoter of the chrAN operon. This observation implies that these residues are crucial for establishing a DNA-binding site. These findings demonstrate that ChrN functions as a transcriptional repressor, modulating the cellular response of strain Z1 to Cr(VI) exposure.

Dependence of Interlayer or Sulfur Host on Hollow Framework of Lithium-Sulfur Battery.

Lithium-sulfur batteries are recognized as the next generation of high-specific energy secondary batteries owing to their satisfactory theoretical specific capacity and energy density. However, their commercial application is greatly limited by a series of problems, including disordered migration behavior, sluggish redox kinetics, and the serious shuttle effect of lithium polysulfides. One of the most efficient approaches to physically limit the shuttle effect is the rational design of a hollow framework as sulfur host. However, the influence of the hollow structure on the interlayers has not been clearly reported. In this study, the Mo2 C/C catalysts with hollow(H-Mo2 C/C) and solid(S-Mo2 C/C) frameworks are rationally designed to explore the dependence of the hollow structure on the interlayer or sulfur host. In contrast to the physical limitations of the hollow framework as host, the hollow structure of the interlayer inhibited lithium-ion diffusion, resulting in poor electrochemical properties at high current densities. Based on the superiority of the various frameworks, the H-Mo2 C/C@S | S-Mo2 C/C@PP | Li cells are assembled and displayed excellent electrochemical performance. This work re-examines the design requirements and principles of catalyst frameworks in different battery units.

Arsenite Mediates Selenite Resistance and Reduction in Enterobacter sp. Z1, Thereby Enhancing Bacterial Survival in Selenium Environments.

Arsenic (As) is widely present in the environment, and virtually all bacteria possess a conserved ars operon to resist As toxicity. High selenium (Se) concentrations tend to be cytotoxic. Se has an uneven regional distribution and is added to mitigate As contamination in Se-deficient areas. However, the bacterial response to exogenous Se remains poorly understood. Herein, we found that As(III) presence was crucial for Enterobacter sp. Z1 to develop resistance against Se(IV). Se(IV) reduction served as a detoxification mechanism in bacteria, and our results demonstrated an increase in the production of Se nanoparticles (SeNPs) in the presence of As(III). Tandem mass tag proteomics analysis revealed that the induction of As(III) activated the inositol phosphate, butanoyl-CoA/dodecanoyl-CoA, TCA cycle, and tyrosine metabolism pathways, thereby enhancing bacterial metabolism to resist Se(IV). Additionally, arsHRBC, sdr-mdr, purHD, and grxA were activated to participate in the reduction of Se(IV) into SeNPs. Our findings provide innovative perspectives for exploring As-induced Se biotransformation in prokaryotes.

Chromate-induced methylglyoxal detoxification system drives cadmium and chromate immobilization by Cupriavidus sp. MP-37.

The detoxification of cadmium (Cd) or chromium (Cr) by microorganisms plays a vital role in bacterial survival and restoration of the polluted environment, but how microorganisms detoxify Cd and Cr simultaneously is largely unknown. Here, we isolated a bacterium, Cupriavidus sp. MP-37, which immobilized Cd(II) and reduced Cr(VI) simultaneously. Notably, strain MP-37 exhibited variable Cd(II) immobilization phenotypes, namely, cell adsorption and extracellular immobilization in the co-presence of Cd(II) and Cr(VI), while cell adsorption in the presence of Cd(II) alone. To unravel Cr(VI)-induced extracellular Cd(II) immobilization, proteomic analysis was performed, and methylglyoxal-scavenging protein (glyoxalase I, GlyI) and a regulator (YafY) showed the highest upregulation in the co-presence of Cd(II) and Cr(VI). GlyI overexpression reduced the intracellular methylglyoxal content and increased the immobilized Cd(II) content in extracellular secreta. The addition of lactate produced by GlyI protein with methylglyoxal as substrate increased the Cd(II) content in extracellular secreta. Reporter gene assay, electrophoretic mobility shift assay, and fluorescence quenching assay demonstrated that glyI expression was induced by Cr(VI) but not by Cd(II), and that YafY positively regulated glyI expression by binding Cr(VI). In the pot experiment, inoculation with the MP-37 strain reduced the Cd content of Oryza sativa L., and their secreted lactate reduced the Cr accumulation in Oryza sativa L. This study reveals that Cr(VI)-induced detoxification system drives methylglyoxal scavenging and Cd(II) extracellular detoxification in Cd(II) and Cr(VI) co-existence environment.

Arsenic Removal via the Biomineralization of Iron-Oxidizing Bacteria Pseudarthrobacter sp. Fe7.

Arsenic (As) is a highly toxic metalloid, and its widespread contamination of water is a serious threat to human health. This study explored As removal using Fe(II)-oxidizing bacteria. The strain Fe7 isolated from iron mine soil was classified as the genus Pseudarthrobacter based on 16S rRNA gene sequence similarities and phylogenetic analyses. The strain Fe7 was identified as a strain of Gram-positive, rod-shaped, aerobic bacteria that can oxidize Fe(II) and produce iron mineral precipitates. X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy patterns showed that the iron mineral precipitates with poor crystallinity consisted of Fe(III) and numerous biological impurities. In the co-cultivation of the strain Fe7 with arsenite (As(III)), 100% of the total Fe and 99.9% of the total As were removed after 72 h. During the co-cultivation of the strain Fe7 with arsenate (As(V)), 98.4% of the total Fe and 96.9% of the total As were removed after 72 h. Additionally, the iron precipitates produced by the strain Fe7 removed 100% of the total As after 3 h in both the As(III) and As(V) pollution systems. Furthermore, enzyme activity experiments revealed that the strain Fe7 oxidized Fe(II) by producing extracellular enzymes. When 2% (v/v) extracellular enzyme liquid of the strain Fe7 was added to the As(III) or As(V) pollution system, the total As removal rates were 98.6% and 99.4%, respectively, after 2 h, which increased to 100% when 5% (v/v) and 10% (v/v) extracellular enzyme liquid of the strain Fe7 were, respectively, added to the As(III) and As(V) pollution systems. Therefore, iron biomineralized using a co-culture of the strain Fe7 and As, iron precipitates produced by the strain Fe7, and the extracellular enzymes of the strain Fe7 could remove As(III) and As(V) efficiently. This study provides new insights and strategies for the efficient remediation of arsenic pollution in aquatic environments.

Toxic response of antimony in the Comamonas testosteroni and its application in soil antimony bioremediation.

Antimony (Sb) is toxic to ecosystems and potentially to public health via its accumulation in the food chain. Bioavailability and toxicity of Sb have been reduced using various methods for the remediation of Sb-contaminated soil in most studies. However, Sb-contaminated soil remediation by microbial agents has been rarely evaluated. In this study, we evaluated the potential for the use of Comamonas testosteroni JL40 in the bioremediation of Sb-contamination. Strain JL40 immobilized more than 30 % of the Sb(III) in solution and oxidized over 18 % to Sb(V) for detoxification. Meanwhile, strain JL40 responds to Sb toxicity through such as Sb efflux, intracellular accumulation, biofilm production, and scavenging of reactive oxygen species (ROS), etc. The results of the pot experiment showed the average Sb content of the brown rice was decreased by 59.1%, 38.8%, and 48.4%, for 1.8, 50, and 100 mg/kg Sb spiked soils, respectively. In addition, the results of plant, soil enzyme activity, and rice agronomic trait observations showed that the application of strain JL40 could maintain the health of plants and soil and improve rice production. The single-step and sequential extraction of Sb from rhizosphere soil showed that strain JL40 also plays a role in Sb immobilization and oxidation in the soil environment. During rice potted cultivation, bacterial community analysis and plate counting showed that the strain JL40 could still maintain 103 CFU/g after 30 days of inoculation. With phenotypic and differential proteomics analysis, strain JL40 conferred Sb(III) tolerance by a combination of immobilization, oxidation, efflux and scavenging of ROS, etc. Our study demonstrates the application of Sb-immobilizing and oxidizing bacteria to lower soil Sb and reduce accumulation of Sb in rice. Our results provide guidance for bacterial remediation of Sb-contaminated soil.

Enterobacter sp. E1 increased arsenic uptake in Pteris vittata by promoting plant growth and dissolving Fe-bound arsenic.

Microbes affect arsenic accumulation in the arsenic-hyperaccumulator Pteris vittata, but the associated molecular mechanism remains uncertain. Here, we investigated the effect of Enterobacter sp. E1 on arsenic accumulation by P. vittata. Strain E1 presented capacities of arsenate [As(V)] and Fe(III) reduction during cultivation. In the pot experiment with P. vittata, the biomass, arsenic content, and chlorophyll content of P. vittata significantly increased by 30.03%, 74.9%, and 112.1%, respectively. Strikingly, the water-soluble plus exchangeable arsenic (WE-As) significantly increased by 52.05%, while Fe-bound arsenic (Fe-As) decreased by 29.64% in the potted soil treated with strain E1. The possible role of activation of arsenic by strain E1 was subsequently investigated by exposing As(V)-absorbed ferrihydrite to the bacterial culture. Speciation analyses of As showed that strain E1 significantly increased soluble levels of As and Fe and that more As(V) was reduced to arsenite. Additionally, increased microbial diversity and soil enzymatic activities in soils indicated that strain E1 posed few ecological risks. These results indicate that strain E1 effectively increased As accumulation in P. vittata mainly by promoting plant growth and dissolving soil arsenic. Our findings suggest that As(V) and Fe(III)-reducer E1 could be used to enhance the phytoremediation of P. vittata in arsenic-contaminated soils.

Multiple mechanisms collectively mediate tungsten homeostasis and resistance in Citrobacter sp. Lzp2.

Tungsten (W) is an emerging contaminant, and current knowledge on W resistance profiles of microorganisms remains scarce and fragmentary. This study aimed to explore the physiological responses of bacteria under W stress and to resolve genes and metabolic pathways involved in W resistance using a transcriptome expression profiling assay. The results showed that the bacterium Citrobacter sp. Lzp2, screened from W-contaminated soil, could tolerate hundreds of mM W(VI) with a 50% inhibiting concentration of ∼110 mM. To cope with W stress, Citrobacter sp. Lzp2 secreted large amounts of proteins through the type VI secretory system (T6SS) to chelate W oxoanions via carboxylic groups in extracellular polymeric substances (EPS), and could transport cytosolic W outside via the multidrug efflux pumps (mdtABC and acrD). Intracellular W is probably bound by chaperone proteins and metal-binding pterin (tungstopterin) through the sulfur relay system. We propose that tetrathionate respiration is a new metabolic pathway for cellular W detoxification likely producing thio-tungstate. We conclude that multiple mechanisms collectively mediate W homeostasis and resistance in Citrobacter sp. Lzp2. Our results have important implications not only for understanding the intricate regulatory network of W homeostasis in microbes but also for bio-recovery and bioremediation of W in contaminated environments.

A Coculture of Enterobacter and Comamonas Species Reduces Cadmium Accumulation in Rice.

The accumulation of cadmium (Cd) in plants is strongly impacted by soil microbes, but its mechanism remains poorly understood. Here, we report the mechanism of reduced Cd accumulation in rice by coculture of Enterobacter and Comamonas species. In pot experiments, inoculation with the coculture decreased Cd content in rice grain and increased the amount of nonbioavailable Cd in Cd-spiked soils. Fluorescence in situ hybridization and scanning electron microscopy detection showed that the coculture colonized in the rhizosphere and rice root vascular tissue and intercellular space. Soil metagenomics data showed that the coculture increased the abundance of sulfate reduction and biofilm formation genes and related bacterial species. Moreover, the coculture increased the content of organic matter, available nitrogen, and potassium and increased the activities of arylsulfatase, ß-galactosidase, phenoloxidase, arylamidase, urease, dehydrogenase, and peroxidase in soils. In subsequent rice transcriptomics assays, we found that the inoculation with coculture activated a hypersensitive response, defense-related induction, and mitogen-activated protein kinase signaling pathway in rice. Heterologous protein expression in yeast confirmed the function of four Cd-binding proteins (HIP28-1, HIP28-4, BCP2, and CID8), a Cd efflux protein (BCP1), and three Cd uptake proteins (COPT4, NRAM5, and HKT6) in rice. Succinic acid and phenylalanine were subsequently proved to inhibit rice divalent Cd [Cd(II)] uptake and activate Cd(II) efflux in rice roots. Thus, we propose a model that the coculture protects rice against Cd stress via Cd immobilization in soils and reducing Cd uptake in rice. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Effective and stable adsorptive removal of Cadmium(II) and Lead(II) using selenium nanoparticles modified by microbial SmtA metallothionein.

Metallothionein SmtA-modified selenium nanoparticles (SmtA-SeNPs), efficient adsorbents for Cd(II) and Pb(II), were synthesized in the present work. The ligand, microbial SmtA protein, was synthesized using an engineered strain Escherichia coli, posing the benefits of simplicity, safety, and high production. SmtA-SeNPs were spheres with diameters between 68.1 and 122.4 nm, containing amino, hydroxyl, and sulfhydryl functional groups with negatively charged (pH > 5). SmtA-SeNPs displayed better adsorption performance than dissociative SmtA and SeNPs. The adsorption of Cd(II) and Pb(II) mainly depends on the electrostatic attractions and the metal chelation of abundant functional groups. The maximum adsorption capacity was 506.3 mg/g for Cd(II) and 346.7 mg/g for Pb(II), which were higher than the values of most nanoparticles. In addition, SmtA-SeNPs were immobilized with a membrane filter to produce a SmtA-SeNPs filter, and the percentage removal of Cd(II) and Pb(II) increased from 26.75% to 98.13% for Cd(II) and from 9.95% to 99.20% compared with the blank filter. Moreover, the SmtA-SeNPs filter was regenerated using subacid deionized water, and the filter exhibited a stable removal ratio of Cd(II) and Pb(II) in ten continuous cycles of Cd(II)- or Pb(II)-containing wastewater treatment. The residual amounts of Cd and Pb met national standard levels of wastewater discharge.

Achieving job-synergistic polysulfides adsorption-conversion within hollow structured MoS2/Co4S3/C heterojunction host for long-life lithium-sulfur batteries.

Lithium-sulfur batteries are considered one of the most promising next-generation energy storage devices owing to their ultrahigh theoretical energy density and environmental friendliness. However, the sluggish electrode reaction kinetics of the sulfur cathode and shuttle effects of lithium polysulfide (LiPSs) restrict their active material utilization and cycling stability. Herein, a hollow, free-standing MoS2/Co4S3/C heterojunction was fabricated and employed as a cathode host for high-performance lithium-sulfur batteries (LSBs). The unique hollow nanostructured MoS2/Co4S3/C can achieve job-synergistic polysulfide adsorption-conversion, in which the conductive nitrogen-doped carbon framework facilitates rapid electron/ion diffusion; polar Co4S3 species provide strong chemisorption capability and endow intrinsic catalytic sites towards LiPSs, and MoS2 serves as a nanocrystal to accelerate the reaction dynamics. As a result, MoS2/Co4S3/C/S exhibited high reversible specific capacities at 2C and was maintained at 394 mAh g-1 after 1000 cycles, with a 0.04% capacity decay rate. Impressively, the high reversible specific capacities with high sulfur loading of 4.1 mg cm-2 were maintained at 906.7 mAh g-1.

Indole-Acetic Acid Promotes Ammonia Removal Through Heterotrophic Nitrification, Aerobic Denitrification With Mixed Enterobacter sp. Z1 and Klebsiella sp. Z2.

Mixed Enterobacter sp. Z1 and Klebsiella sp. Z2 displayed an outstanding ammonia removal capacity than using a single strain. Metabolomics, proteomics, and RNA interference analysis demonstrated that the HNAD process was closely related to indole-acetic acid (IAA). Under the cocultured conditions, the excess IAA produced by Z2 could be absorbed by Z1 to compensate for the deficiency of IAA in the cells. IAA directly induced the expression of denitrifying enzymes and further activated the IAA metabolism level, thus greatly improving the nitrogen removal ability of Z1. In turn, nitrate and nitrite induced the expression of key enzymes in the IAA pathways. Moreover, Z1 and Z2 enhanced two IAA metabolic pathways in the process of mixed removal process. The activated hydrolysis-redox pathway in Z1 reduced the oxidative stress level, and the activated decarboxylation pathway in Z2 promoted intracellular energy metabolism, which indirectly promoted the process of HNAD in the system.

Simultaneous removal of nitrogen and arsenite by heterotrophic nitrification and aerobic denitrification bacterium Hydrogenophaga sp. H7.

Introduction: Nitrogen and arsenic contaminants often coexist in groundwater, and microbes show the potential for simultaneous removal of nitrogen and arsenic. Here, we reported that Hydrogenophaga sp. H7 was heterotrophic nitrification and aerobic denitrification (HNAD) and arsenite [As(III)] oxidation bacterium. Methods: The appearance of nitrogen removal and As(III) oxidation of Hydrogenophaga sp. H7 in liquid culture medium was studied. The effect of carbon source, C/N ratio, temperature, pH values, and shaking speeds were analyzed. The impact of strains H7 treatment with FeCl3 on nitrogen and As(III) in wastewater was assessed. The key pathways that participate in simultaneous nitrogen removal and As(III) oxidation was analyzed by genome and proteomic analysis. Results and discussion: Strain H7 presented efficient capacities for simultaneous NH4 +-N, NO3 --N, or NO2 --N removal with As(III) oxidation during aerobic cultivation. Strikingly, the bacterial ability to remove nitrogen and oxidize As(III) has remained high across a wide range of pH values, and shaking speeds, exceeding that of the most commonly reported HNAD bacteria. Additionally, the previous HNAD strains exhibited a high denitrification efficiency, but a suboptimal concentration of nitrogen remained in the wastewater. Here, strain H7 combined with FeCl3 efficiently removed 96.14% of NH4 +-N, 99.08% of NO3 --N, and 94.68% of total nitrogen (TN), and it oxidized 100% of As(III), even at a low nitrogen concentration (35 mg/L). The residues in the wastewater still met the V of Surface Water Environmental Quality Standard of China after five continuous wastewater treatment cycles. Furthermore, genome and proteomic analyses led us to propose that the shortcut nitrification-denitrification pathway and As(III) oxidase AioBA are the key pathways that participate in simultaneous nitrogen removal and As(III) oxidation.

Reducing cadmium in rice using metallothionein surface-engineered bacteria WH16-1-MT.

Cadmium (Cd) accumulation in rice grains poses a health risk for humans. In this study, a bacterium, Alishewanella sp. WH16-1-MT, was engineered to express metallothionein on the cell surface. Compared with the parental WH16-1 strain, Cd2+ adsorption efficiency of WH16-1-MT in medium was increased from 1.2 to 2.6 mg/kg dry weight. The WH16-1-MT strain was then incubated with rice in moderately Cd-contaminated paddy soil. Compared with WH16-1, inoculation with WH16-1-MT increased plant height, panicle length and thousand-kernel weight, and decreased the levels of ascorbic acid and glutathione and the activity of peroxidase. Compared with WH16-1, WH16-1-MT inoculation significantly reduced the concentrations of Cd in brown rice, husks, roots and shoots by 44.0 %, 45.5 %, 36.1 % and 47.2 %, respectively. Moreover, inoculation with WH16-1-MT reduced the bioavailability of Cd in soil, with the total Cd proportion in oxidizable and residual states increased from 29 % to 32 %. Microbiome analysis demonstrated that the addition of WH16-1-MT did not significantly alter the original bacterial abundance and community structure in soil. These results indicate that WH16-1-MT can be used as a novel microbial treatment approach to reduce Cd in rice grown in moderately Cd-contaminated paddy soil.

Cd immobilization mechanisms in a Pseudomonas strain and its application in soil Cd remediation.

In this study, we isolated a highly cadmium (Cd)-resistant bacterium, Pseudomonas sp. B7, which immobilized 100% Cd(II) from medium. Culturing strain B7 with Cd(II) led to the change of functional groups, mediating extracellular Cd(II) adsorption. Proteomics showed that a carbonic anhydrase, CadW, was upregulated with Cd(II). CadW expression in Escherichia coli conferred resistance to Cd(II) and increased intracellular Cd(II) accumulation. Fluorescence assays demonstrated that CadW binds Cd(II) and the His123 residue affected Cd(II) binding activity, indicating that CadW participates in intracellular Cd(II) sequestration. Chinese cabbage pot experiments were performed using strain B7 and silicate [Si(IV)]. Compared with the control, Cd content in aboveground parts significantly decreased by 21.3%, 29.4% and 32.9%, and nonbioavailable Cd in soil significantly increased by 129.4%, 45.0% and 148.7% in B7, Si(IV) and B7 +Si(IV) treatments, respectively. The application of Si(IV) alone reduced chlorophyll content by 20.8% and arylsulfatase activity in soil by 33.9%, and increased malonaldehyde activity by 15.0%. The application of strain B7 alleviated the negative effect of Si(IV) on plant and soil enzymes. Overall, application of Si(IV) is most conducive to the decreased Cd accumulation in plant, and strain B7 is beneficial to maintaining soil and plant health.

Co4 N-Decorated 3D Wood-Derived Carbon Host Enables Enhanced Cathodic Electrocatalysis and Homogeneous Lithium Deposition for Lithium-Sulfur Full Cells.

The sluggish kinetics of sulfur conversion in the cathode and the nonuniform deposition of lithium metal at the anode result in severe capacity decay and poor cycle life for lithium-sulfur (Li-S) batteries. Resolving these deficiencies is the most direct route toward achieving practical cells of this chemistry. Herein, a vertically aligned wood-derived carbon plate decorated with Co4 N nanoparticles host (Co4 N/WCP) is proposed that can serve as a host for both the sulfur cathode and the metallic lithium anode. This Co4 N/WCP electrode host drastically enhances the reaction kinetics in the sulfur cathode and homogenizes the electric field at the anode for the uniform lithium plating. Density functional theory calculations confirm the experimental observations that Co4 N/WCP provides a lower energy barrier for the polysulfide redox reaction in the cathode and a low adsorption energy for lithium deposition at the anode. Employing the Co4 N/WCP host at both electrodes in a S@Co4 N/WCP||Li@Co4 N/WCP full cell delivers a specific capacity of 807.9 mAh g-1 after 500 cycles at a 1 C rate. Additional experiments are performed with high areal sulfur loading of 4 mg cm-2 to demonstrate the viability of this strategy for producing practical Li-S cells.

Balanced capture and catalytic ability toward polysulfides by designing MoO2-Co2Mo3O8 heterostructures for lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries, as the next generation of energy storage systems, are currently limited by insufficient capture ability and sluggish catalytic reaction kinetics, thus leading to serve the shuttle effect of lithium polysulfides (LiPSs). Realizing the accelerated conversion of polysulfides in the cathode host of Li-S batteries is an effective way to improve its coulombic efficiency. The essence of fast conversion relies on enhanced oxidation reaction kinetics by virtue of the metal catalyst, but the generation of various intermediates exacerbate the complexity of the system and perplex the perfect operation of batteries relying on only one catalyst. In this work, the xMoO2:yCo2Mo3O8 heterostructures were designed, in which controlling the content of cobalt could balance the capture capability towards LiPSs by MoO2 and catalytic ability of liquid-solid conversion by Co2Mo3O8 catalytic sites. Therefore, utilizing synergy effect of MoO2-Co2Mo3O8 heterostructure enhances capture and catalytic ability toward polysulfides in Li-S batteries. As a result, the 9MoO2:2Co2Mo3O8-based cathode delivers excellent reversibility of 880 mA h g-1 after 100 cycles at 0.2C and 509 mA h g-1 after 1000 cycles at 1C with 0.056% capacity decay each cycle. This work provides a new method for synthesizing heterostructures by doping metals. Moreover, it promotes the understanding of balancing and promoting the capture capacity and catalytic conversion ability toward LiPSs.

NemA Catalyzes Trivalent Organoarsenical Oxidation and Is Regulated by the Trivalent Organoarsenical-Selective Transcriptional Repressor NemR.

Synthetic aromatic arsenicals such as roxarsone (Rox(V)) and nitarsone (Nit(V)) have been used as animal growth enhancers and herbicides. Microbes contribute to redox cycling between the relatively less toxic pentavalent and highly toxic trivalent arsenicals. In this study, we report the identification of nemRA operon from Enterobacter sp. Z1 and show that it is involved in trivalent organoarsenical oxidation. Expression of nemA is induced by chromate (Cr(VI)), Rox(III), and Nit(III). Heterologous expression of NemA in Escherichia coli confers resistance to Cr(VI), methylarsenite (MAs(III)), Rox(III), and Nit(III). Purified NemA catalyzes simultaneous Cr(VI) reduction and MAs(III)/Rox(III)/Nit(III) oxidation, and oxidation was enhanced in the presence of Cr(VI). The results of electrophoretic mobility shift assays and fluorescence assays demonstrate that the transcriptional repressor, NemR, binds to either Rox(III) or Nit(III). NemR has three conserved cysteine residues, Cys21, Cys106, and Cys116. Mutation of any of the three resulted in loss of response to Rox(III)/Nit(III), indicating that they form an Rox(III)/Nit(III) binding site. These results show that NemA is a novel trivalent organoarsenical oxidase that is regulated by the trivalent organoarsenical-selective repressor NemR. This discovery expands our knowledge of the molecular mechanisms of organoarsenical oxidation and provides a basis for studying the redox coupling of environmental toxic compounds.

Comamonas testosteroni antA encodes an antimonite-translocating P-type ATPase.

Antimony, like arsenic, is a toxic metalloid widely distributed in the environment. Microbial detoxification of antimony has recently been identified. Here we describe a novel bacterial P1B-type antimonite (Sb(III))-translocating ATPase from the antimony-mining bacterium Comamonas testosterone JL40 that confers resistance to Sb(III). In a comparative proteomics analysis of strain JL40, an operon (ant operon) was up-regulated by Sb(III). The ant operon includes three genes, antR, antC and antA. AntR belongs to the ArsR/SmtB family of metalloregulatory proteins that regulates expression of the ant operon. AntA belongs to the P1B family of the P-type cation-translocating ATPases. It has both similarities to and differences from other members of the P1B-1 subfamily and appears to be the first identified member of a distinct subfamily that we designate P1B-8. Expression AntA in E. coli AW3110 (Δars) conferred resistance to Sb(III) and reduced the intracellular concentration of Sb(III) but not As(III) or other metals. Everted membrane vesicles from cells expressing antA accumulated Sb(III) but not As(III), where uptake in everted vesicles reflects efflux from cells. AntC is a small protein with a potential Sb(III) binding site, and co-expression of AntC with AntA increased resistance to Sb(III). We propose that AntC functions as an Sb(III) chaperone to AntA, augmenting Sb(III) efflux. The identification of a novel Sb(III)-translocating ATPase enhances our understanding of the biogeochemical cycling of environmental antimony by bacteria.

Microbial Oxidation of Arsenite: Regulation, Chemotaxis, Phosphate Metabolism and Energy Generation.

Arsenic (As) is a metalloid that occurs widely in the environment. The biological oxidation of arsenite [As(III)] to arsenate [As(V)] is considered a strategy to reduce arsenic toxicity and provide energy. In recent years, research interests in microbial As(III) oxidation have been growing, and related new achievements have been revealed. This review focuses on the highlighting of the novel regulatory mechanisms of bacterial As(III) oxidation, the physiological relevance of different arsenic sensing systems and functional relationship between microbial As(III) oxidation and those of chemotaxis, phosphate uptake, carbon metabolism and energy generation. The implication to environmental bioremediation applications of As(III)-oxidizing strains, the knowledge gaps and perspectives are also discussed.