Aggregation-regulated bioreduction process of graphene oxide by Shewanella bacteria

The bioreduction of graphene oxide(GO)using environmentally functional bacteria such as Shewanella represents a green approach to produce reduced graphene oxide(rGO).This process differs from the chemical reduction that involves instantaneous molecular reactions.In bioreduction,the contact of bacterial cells and GO is considered the rate-limiting step.To reveal how the bacteria-GO integration regulates rGO production,the comparative experiments of GO and three Shewanella strains were carried out.Fourier-transform infrared spectroscopy,X-ray photoelectron spectroscopy,Raman spectroscopy,and atomic force microscopy were used to characterize the reduction degree and the aggregation degree.The results showed that a spontaneous aggregation of GO and Shewanella into the condensed entity occurred within 36 h.A positive linear correlation was established,linking three indexes of the aggregation potential,the bacterial reduction ability,and the reduction degree(ID/IG)comprehensively.

Rapid Preparation Process of Silver Nanoparticles by Bioreduction and Their Characterizations

Bioreduction as a novel nanoparticle synthesizing technology attracts increasing attention. Dried cells of the bacterium Aeromonas sp. SH10 rapidly reduced [Ag（NH3）2]^＋ to Ago in the solution into which some amount of OH^- was introduced. The surface plasmon resonance centered at 425 nm on the UV-vis spectra and five broad Bragg reflections on the XRD pattern showed that stable silver nanoparticles were formed during the bioreduction process. TEM and SEM observations suggested that the silver nanoparticles were uniform in size and well dispersed on the cells and in the solution. Therefore, silver nanoparticles could be prepared rapidly by this bioreduction technology.

Asymmetric bioreduction of substituted acenaphthenequinones using plant enzymatic systems:A novel strategy for the preparation of(+)- and(-)-mono hydroxyacenaphthenones

Regio- and enantioselective reduction of substituted acenaphthenequinones were conducted under mild reaction conditions using plant enzymatic systems. A screening of 15 plants allowed the selection of two suitable plants fulfilling enantiocomple- mentarity. The （＋）- and （-）-mono hydroxyacenaphthenones were achieved with high conversion and good enantiomeric purity using peach （Prunus persica （L.） Batsch., conversion 98%, 71% ee） and carrot （Daucus carota L., conversion 95%, 81% ee）, respectively.

The biochemical behavior and mechanism of uranium(Ⅵ)bioreduction induced by natural Bacillus thuringiensis

For a broader understanding of uranium migration affected by microorganisms in natural anaerobic environment,the bioreduction of uranium(Ⅵ)(U(Ⅵ))was revealed in Bacillus thuringiensis,a dominant bacterium strain with potential of uranium-tolerant isolated from uranium contaminated soil.The reduction behavior was systematically investigated by the quantitative analysis of U(Ⅳ)in bacteria,and mechanism was inferred from the pathway of electron transmission.Under anaerobic conditions,appropriate biomass and sodium lactate as electron donor,reduction behavior of U(Ⅵ)induced by B.thuringiensis was restricted by the activity of lactate dehydrogenase,which was directly affected by the initial pH,temperature and initial U(Ⅵ)concentration of bioreduction system.Bioreduction of U(Ⅵ)was driven by the generation of nicotinamide adenine dinucleotide(NADH)from enzymatic reaction of sodium lactate with various dehydrogenase.The transmission of the electrons from bacteria to U(Ⅵ)was mainly supported by the intracellular NADH dehydrogenase-ubiquinone system,this process could maintain the biological activity of cells.

Contribution of redox-active properties of compost-derived humic substances in hematite bioreduction

The compost-derived humic substances(HS)can function as electron mediators for promoting hematite bioreduction because of its redox capacity.Humification process can affect redox capacities of compost-derived HS by changing its intrinsic structure.However,the redox properties of compost-derived HS link-ing with hematite bioreduction during composting still remain unclear.Herein,we investigated the redox capacities of compost-derived HS,and assessed the responses of the redox capacities to the hematite bioreduction.The result showed that compost-derived HS(i.e.,humic acids(HA)and fulvic acids(FA))were able to accept electrons from Shewanella oneidensis MR-1,and the electron accepting capacity was increased during composting.Furthermore,it could be functioned as electron mediators for promoting the hematite bioreduction,achieving 1.19-2.15 times compared with the control experience.Not only the aromatic structures(quinone)but also the non-quinone structures such as nitrogen-and sulfur-containing functional moieties were served as the redox-active functional groups of compost-derived HS.Our work proved that the aromatic functional groups and the heteroatom structures(especially N)were important to the hematite bioreduction.This study highlights the redox-active properties of compost-derived HS and its impact on the microbial reduction of iron mineral.Redox capacity of compost-derived HS might mitigate the environmental risk of contaminants when the composting production was added into the contaminated soils as low-cost repair materials.

Bioreduction of vanadium(V) in groundwater by autohydrogentrophic bacteria:Mechanisms and microorganisms

As one of the transition metals, vanadium（V）（V（V）） in trace amounts represents an essential element for normal cell growth, but becomes toxic when its concentration is above 1 mg/L. V（V） can alter cellular differentiation, gene expression, and other biochemical and metabolic phenomena. A feasible method to detoxify V（V） is to reduce it to V（IV）, which precipitates and can be readily removed from the water. The bioreduction of V（V） in a contaminated groundwater was investigated using autohydrogentrophic bacteria and hydrogen gas as the electron donor. Compared with the previous organic donors,H2 shows the advantages as an ideal electron donor, including nontoxicity and less production of excess biomass. V（V） was 95.5% removed by biochemical reduction when autohydrogentrophic bacteria and hydrogen were both present, and the reduced V（IV）precipitated, leading to total-V removal. Reduction kinetics could be described by a first-order model and were sensitive to p H and temperature, with the optimum ranges of p H 7.5–8.0 and 35–40°C, respectively. Phylogenetic analysis by clone library showed that the dominant species in the experiments with V（V） bioreduction belonged to theβ-Proteobacteria. Previously known V（V）-reducing species were absent, suggesting that V（V）reduction was carried out by novel species. Their selective enrichment during V（V）bioreduction suggests that Rhodocyclus, a denitrifying bacterium, and Clostridium, a fermenter known to carry out metal reduction, were responsible for V（V） bioreduction.

Uranium sequestration in sediment at an iron-rich contaminated site at Oak Ridge, Tennessee via.bioreduction followed by reoxidation

This study evaluated uranium sequestration performance in iron-rich (30 g/kg) sediment via bioreduction followed by reoxidation.Field tests (1383 days) at Oak Ridge,Tennessee demonstrated that uranium contents in sediments increased after bioreduced sediments were re-exposed to nitrate and oxygen in contaminated groundwater.Bioreduction of contaminated sediments (1200 mg/kg U) with ethanol in microcosm reduced aqueous U from 0.37 to 0.023 mg/L.Aliquots of the bioreduced sediment were reoxidized with O2,H2O2,and NaNO3,respectively,over 285 days,resulting in aqueous U of 0.024,1.58 and 14.4 mg/L at pH 6.30,6.63 and 7.62,respectively.The source-and the three reoxidized sediments showed different desorption and adsorption behaviors of U,but all fit a Freundlich model.The adsorption capacities increased sharply at pH 4.5 to 5.5,plateaued at pH 5.5 to 7.0,then decreased sharply as pH increased from 7.0 to 8.0.The O2-reoxidized sediment retained a lower desorption efficiency at pH over 6.0.The NO3--reoxidized sediment exhibited higher adsorption capacity at pH 5.5 to 6.0.The pH-dependent adsorption onto Fe(Ⅲ) oxides and formation of U coated particles and precipitates resulted in U sequestration,and bioreduction followed by reoxidation can enhance the U sequestration in sediment.

Bioreduction of hexavalent chromium:Effect of compost-derived humic acids and hematite

Composting can enhance the nutrie nt ele ments cycling and reduce carbon dioxide production.However,little information is available regarding the application of compost for the remediation of the contaminated soil.In this study,we assess the response of the redox capacities(electron accepting capacities(EAC)and electron donating capacities(EDC))of compost-derived humic acids(HAs)to the bioreduction of hexavalent chromium(Cr(Ⅵ)),especially in presence of hematite.The result showed that the compost-derived HAs played an important role in the bioreduction of Cr(Ⅵ)in presence and absence of hematite under the anoxic,neutral(pH 7)and motionless conditions.Based on the pseudo-first order kinetic model,the rate constants of Cr(Ⅵ)reduction increased by 1.36-2.0 times when compost-derived HAs was added.The redox capacity originating from the polysaccharide structure of compost-derived HAs made them effective in the direct Cr(Ⅵ)reduction(without MR-1)at pH 7.Meanwhile,the reduction rates were inversely proportional to the composting treatment time.When iron mineral(Fe_(2)O_(3))and compost-derived HAs were both present,the rate constants of Cr(Ⅵ)reduction increased by 2.35-5.09,which were higher than the rate of Cr(Ⅵ)reduction in HA-only systems,indicating that the hematite played a crucial role in the bioreduction process of Cr(Ⅵ).EAC and quinonoid structures played a major role in enhancing the bioreduction of Cr(Ⅵ)when iron mineral and compost-derived HAs coexisted in the system.The results can extend the application fields of compost and will provide a new insight for the remediation of Cr(Ⅵ)-contaminated soil.

Contributions of adsorption, bioreduction and desorption to uranium immobilization by extracellular polymeric substances

Hexavalent uranium(U(VI))can be immobilized by various microbes.The role of extracellular polymeric substances(EPS)in U(VI)immobilization has not been quantified.This work provides a model framework to quantify the contributions of three processes involved in EPS-mediated U(VI)immobilization:adsorption,bioreduction and desorption.Loosely associated EPS was extracted from a pure bacterial strain,Klebsiella sp.J1,and then exposed to H_(2) and O_(2)(no bioreduction control)to immobilize U(VI)in batch experiments.U(VI)immobilization was faster when exposed to H_(2) than O_(2) and stabilized at 94%for H_(2) and 85%for O_(2),respectively.The non-equilibrium data from the H_(2) experiments were best simulated by a kinetic model consisting of pseudo-second-order adsorption(ka=2.87×10^(−3) g EPS·(mg U)^(−1)·min^(−1)),first-order bioreduction(kb=0.112 min−1)and first-order desorption(kd=7.00×10^(−3) min^(−1))and fitted the experimental data with R^(2) of 0.999.While adsorption was dominant in the first minute of the experiments with H_(2),bioreduction was dominant from the second minute to the 50th min.After 50 min,adsorption was negligible,and bioreduction was balanced by desorption.This work also provides the first set of equilibrium data for U(VI)adsorption by EPS alone.The equilibrium experiments with O_(2) were well simulated by both the Langmuir isotherm and the Freundlich isotherm,suggesting multiple mechanisms involved in the interactions between U(VI)and EPS.The thermodynamic study indicated that the adsorption of U(VI)onto EPS was endothermic,spontaneous and favorable at higher temperatures.

Bioreduction of quinone derivatives by immobilized Baker's yeast in hexane

Immobilization techniques and biocatalytic transformations performed in organic media are new developing methods for organic reactions. Baker's yeast was immobilized on the alginate supports. This preparation contained about 20% of dry yeast cells. The immobilized Baker's yeast were found to be very effective in the reduction of o-benzoquinone, p-benzoquinones, naphthoquinones, and anthraquinones in hexane.

Biofabrication of Ag nanoparticles using Moringa oleifera leaf extract and their antimicrobial activity

Objective:To formulate a simple rapid procedure for bioreduction of silver nanoparticles using aqueous leaves extract of Moringa oleifera(M.oleifera).Methods:10 mL of leaf extract was mixed to 90 mL of 1 mM aqueous of AgNO_3 and was heated at 60-80 ℃ for 20 min.A change from brown to reddish color was observed.Characterization using UV-Vis spectrophotometry, Transmission Electron Microscopy(TEM) was performed.Results:TEM showed the formation of silver nanoparticles with an average size of 57 nm.Conclusions:M.oleifera demonstrates strong potential for synthesis of silver nanoparticles by rapid reduction of silver ions(Ag^+ to Ag^0). Biological methods are good competents for the chemical procedures,which are eco-friendly and convenient.

A Study of Pt^(4+)Adsorption and Its Reduction by Bacillus Megaterium D01

The properties of Pt 4+ adsorption and its reduction by Bacillus megaterium D01 were studied by means of ICP, anode stripping voltammetry, TEM, IR and XPS. The results of ICP analyses showed that the Pt 4+ adsorptive efficiency of the strain D01 was as high as 94.3% under the conditions of 100 mg Pt 4+ /L, 1 g biomass/L, pH 3.5 and at 30 ℃ for 24 h. Moreover, it was confirmed from anode stripping voltammetry that the strain D01 possessed a strong reducibility. The TEM analysis indicated that the strain D01 was able to adsorb and reduce Pt 4+ to Pt 0, small particles. The XPS result further supported the reduction of Pt 4+ to Pt 2+ , followed by the further recuction to Pt 0. The IR spectrum implied that D01 biomass adsorption of Pt 4+ may result in the complexation of the CO bond to the Pt species.

Production of Chiral Aromatic Alcohol by Asymmetric Reduction with Vegetable Catalyst

Chiral aromatic alcohols are the key chiral building block for many important enantiopure pharmaceu-ticals. In this work,we studied asymmetric reduction of prochiral aromatic ketone to produce the corresponding chiral alcohol using vegetables as the biocatalyst. Acetophenone was chosen as the model substrate. The results in-dicate that acetophenone can be reduced to the corresponding chiral alcohols with high enantioselectivity by the chosen vegetables,i.e. apple(Malus pumila),carrot(Daucus carota),cucumber(Cucumis sativus),onion(Allium cepa),potato(Soanum tuberosum),radish(Raphanus sativus),and sweet potato(Ipomoea batatas) . In the reaction,R-1-phenylethanol is produced with apple,sweet potato and potato as the catalyst,while S-1-phenylethanol is the product with the other vegetables as the catalyst. In term of the enantioselectivity and reaction yield,carrot(D. ca-rota) is the best catalyst for this reaction. Furthermore,the reaction characteristics were studied in detail using car-rot(D. carota) as the biocatalyst. The effects of various factors on the reaction were investigated and the optimal reaction conditions were determined. Under the optimal reaction conditions(reaction time 50 h,substrate concen-tration 20 mmol·L-1,reaction temperature 35 °C and pH 7),95% of e.e.(to S-1-phenylethanol) and 85% chemical yield can be obtained. This work extends the biocatalyst for the asymmetric reduction reaction of prochiral aromatic ketones,and provides a novel potential route to produce enantiopure aromatic alcohols.

Soybean (<i>Glycine Max</i>) Leaf Extract Based Green Synthesis of Palladium Nanoparticles

Palladium (Pd) nanoparticles were synthesized using protein rich soybean leaf extract based biological process. Reduction of palladium ions by soybean leaf extract was examined by UV-visible spectroscopic technique. It was believed that the proteins and some of the amino acids that are exist in soybean leaf extracts were actively involved in the reduction of palladium ions. Further it was confirmed by Fourier transformations infrared spectroscopic (FTIR) analysis. These amino acids are not only involving in the reduction of palladium ions but also acting as surfactants that inhibits the rapid agglomeration. The phase purity of the synthesized palladium nanoparticles was investigated through X-Ray Diffraction (XRD) analysis and the obtained pattern was compared with JCPDS data. Transmission electron microscopic (TEM) images of the palladium particles were recorded and the particle size was found to be ~15 nm.

Green Process for Impregnation of Silver Nanoparticles into Microcrystalline Cellulose and Their Antimicrobial Bionanocomposite Films

A novel greener method to impregnate silver nanoparticles (AgNPs) into microcrystalline cellulose (MCC) by curry leaf (Murraya koenigii) extract mediated biological process is presented. The active reduction of silver ions by curry leaf extract was explored for the in situ impregnation AgNPs into MCC. Transmission electron microscopy (TEM) analyses of MCC coated with AgNPs showed the formation of silver particle sizes in the range of 10-25 nm and have a spherical shape. Further the, EDS analysis of MCC/Ag nanocomposite confirms the formation of Ag structure on microcrystalline cellulose. Solvent casting of poly(lactic-acid) was used to produce composite films containing silver impregnated MCC aiming for antimicrobial applications.

Simultaneous removal of critical rare earth elements and chalcogen oxyanions by anaerobic granular sludge

Conventional mining of economically and strategically important critical rare earth elements(REEs)(such as neodymium,lanthanum and dysprosium),and chalcogens(such as selenium and tellurium)are associated with a huge economic and environmental cost.Therefore,the need to recover REEs as well as chalcogens from different waste streams including wastewaters is becoming urgent.Batch assays on synthetic chalcogen/REE-laden wastewater showed that the presence of REEs significantly improved the tellurite removal rate(>80%)and enhanced selenate removal by 66%±10%.Three 3.9 L continuous upflow anaerobic granular sludge bed(UASB)reactors were operated at a hydraulic retention time of 24 h and 30℃.Selenate reduction was achieved with a removal efficiency of~98% with an influent p H of 4.0 for more than 28 days.The effect of REEs on tellurite removal in the UASB bioreactor could not be clearly established since a soluble tellurium removal efficiency of more than 98%was observed already before the addition of REEs at elevated tellurite concentrations.The complete REE removal in both batch assays and UASB reactors at higher pH(7.0±0.5)was attributed to precipitation,whereas chalcogen oxyanions removal was due to microbial reduction.However,at acidic p H,biosorption was responsible for REE's removal,and the Se-enriched sludge exhibited a superior REE's removal efficiency than the non-enriched and Te-enriched sludge.

Microbial-driven ectopic uranium extraction with net electrical energy production

The extraction of uranium (U) from U-bearing wastewater is of paramount importance for mitigating negative environmental impacts and recovering U resources. Microbial reduction of soluble hexavalent uranium (U(VI)) to insoluble tetravalent uranium (U(IV)) holds immense potential for this purpose, but its practical application has been impeded by the challenges associated with managing U-bacterial mixtures and the biotoxicity of U. To address these challenges, we present a novel spontaneous microbial electrochemical (SMEC) method that spatially decoupled the microbial oxidation reaction and the U(VI) reduction reaction. Our results demonstrated stable and efficient U extraction with net electrical energy production, which was achieved with both synthetic and real wastewater. U(VI) removal occurred via diffusion-controlled U(VI)-to-U(IV) reduction-precipitation at the cathode, and the UIVO_(2) deposited on the surface of the cathode contributed to the stability and durability of the abiotic U(VI) reduction. Metagenomic sequencing revealed the formation of efficient electroactive communities on the anodic biofilm and enrichment of the key functional genes and metabolic pathways involved in electron transfer, energy metabolism, the TCA cycle, and acetate metabolism, which indicated the ectopic reduction of U(VI) at the cathode. Our study represents a significant advancement in the cost-effective recovery of U from U(VI)-bearing wastewater and may open a new avenue for sustainable uranium extraction.

Adsorption and reduction of palladium (Pd^(2+)) by Bacillus licheniformis R08

Preliminary study on the mechanism of Pd2+ biosorption by resting cells of Bacillus licheniformis R08 biomass has been carried out by means of chemical kinetics and AAS, TEM, XRD and FTIR methods. The results showed that at 30°C and pH 3.5, when dry R08 biomass powder (800 mg/L) was mixed with Pd2+ (100 mg/L) for 45 min, the rate constant k of biosorption of Pd2+ attained a maximum of 5.97×10-2 min-1 and the half life period of the reaction reached 12 min. The part of Pd2+ adsorbed by R08 biomass was reduced to elemental, cell-bound Pd0 at the same condition. The cell wall of R08 biomass was the primary location for accumulating Pd2+, and aldoses, i. e. hy-drolysate of a part of polysaccharides on the peptidoglycan layer in the acidic medium, serving as the electron donor, in situ reduced the Pd2+ to Pd0.

Anaerobic oxidation of arsenite by bioreduced nontronite

The redox state of arsenic controls its toxicity and mobility in the subsurface environment. Understanding the redox reactions of arsenic is particularly important for addressing its environmental behavior. Clay minerals are commonly found in soils and sediments, which are an important host for arsenic. However, limited information is known about the redox reactions between arsenic and structural Fe in clay minerals. In this study, the redox reactions between As(Ⅲ)/As(Ⅴ) and structural Fe in nontronite NAu-2 were investigated in anaerobic batch experiments. No oxidation of As(Ⅲ) was observed by the native Fe(Ⅲ)-NAu-2. Interestingly, anaerobic oxidation of As(Ⅲ) to As(Ⅴ) occurred after Fe(Ⅲ)-NAu-2 was bioreduced. Furthermore, anaerobic oxidization of As(Ⅲ) by bioreduced NAu-2 was significantly promoted by increasing Fe(Ⅲ)-NAu-2 reduction extent and initial As(Ⅲ) concentrations. Bioreduction of Fe(Ⅲ)-NAu-2 generated reactive Fe(Ⅲ)-O-Fe(Ⅱ) moieties at clay mineral edge sites. Anaerobic oxidation of As(Ⅲ) was attributed to the strong oxidation activity of the structural Fe(Ⅲ) within the Fe(Ⅲ)-O-Fe(Ⅱ) moieties. Our results provide a potential explanation for the presence of As(Ⅴ) in the anaerobic subsurface environment. Our findings also highlight that clay minerals can play an important role in controlling the redox state of arsenic in the natural environment.

Chemoenzymatic synthesis of Ro 25-8210 and Ro 25-6630

Here we report the chemoenzymatic synthesis of Ro 25-8210 (1) and Ro 25-6630 (2) by using microbial reduction of α-chloromethyl ketone 4 mediated with baker’s yeast andGeotrichum sp. to afford the optically active (R) and (S)-α-chlorohydrin 8 respectively as the key step.