Kinetic studies on the electron transfer between bacterial c-type cytochromes and metal oxides (original) (raw)
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Electrochimica Acta, 2002
Cytochromes c 3 are polyheme c-type cytochromes characterized by low redox potentials, that have been shown to develop metalreductase activity. In this paper, different strategies are explored to immobilize one of them, Desulfovibrio vulgaris Hildenborough cytochrome c 3 , a highly basic tetraheme cytochrome, including adsorption, covalent bonding, imprisonment in a layer-by-layer assembly, and entrapment within cast films or a dialysis membrane. The performance and efficiency of modified (carbon or gold) electrodes have been evaluated using electrochemical (cyclic and square-wave voltammetry, current Á/time curves) techniques in the presence of a soluble Fe(III) complex, ammonium Fe(III) citrate acting as the soluble substrate, and chosen as a model system. The advantages and drawbacks of each strategy are discussed with the view of further extension of environmental interest to more toxic metal contaminants. #
Bioremediation of chromate by sulfate-reducing bacteria, cytochromes c 3 and hydrogenases
Water, Air, & Soil …, 2003
The treatment of soils and ground waters polluted by heavy metals is of economical and environmental interest. Reduction of Cr(VI) to the less toxic Cr(III) associated to its precipitation is a potentially useful process for bioremediation. In order to develop ecological processes using micro-organisms, we have compared various sulfate-reducing bacteria for enzymatic reduction of chromate. The best Cr(VI) reductase activity was obtained with Desulfomicrobium norvegicum. Despite morphological changes induced by the presence of chromate, this strain can grow in the presence of up to 500 µM Cr(VI) and can decontaminate waters polluted by Cr(VI) when seeded in bioreactors. We have demonstrated the ability of several metalloenzymes (cytochromes c 3 and hydrogenases) to reduce chromate. Biophysical investigations of the chromate/protein interaction in order to get further informations on the mechanism of metal reduction by cytochromes c 3 are under the way.
Applied Microbiology and Biotechnology, 2006
Toxic heavy metals constitute a worldwide environmental pollution problem. Bioremediation technologies represent efficient alternatives to the classic cleaningup of contaminated soil and ground water. Most toxic heavy metals such as chromium are less soluble and toxic when reduced than when oxidized. Sulfate-reducing bacteria (SRB) are able to reduce heavy metals by a chemical reduction via the production of H 2 S and by a direct enzymatic process involving hydrogenases and c 3 cytochromes. We have previously reported the effects of chromate [Cr(VI)] on SRB bioenergetic metabolism and the molecular mechanism of the metal reduction by polyhemic cytochromes. In the current work, we pinpoint the bacteria-metal interactions using Desulfovibrio vulgaris strain Hildenborough as a model. The bacteria were grown in the presence of high Cr(VI) concentration, where they accumulated precipitates of a reduced form of chromium, trivalent chromium [Cr(III)], on their cell surfaces. Moreover, the inner and outer membranes exhibited precipitates that shared the spectroscopic signature of trivalent chromium. This subcellular localization is consistent with enzymatic metal reduction by cytochromes and hydrogenases. Regarding environmental significance, our findings point out the Cr(VI) immobilization mechanisms of SRB; suggesting that SRB are highly important in metal biogeochemistry.
Applied and Environmental Microbiology, 2004
Kinetic parameters and the role of cytochrome c 3 in sulfate, Fe(III), and U(VI) reduction were investigated in Desulfovibrio vulgaris Hildenborough. While sulfate reduction followed Michaelis-Menten kinetics (K m ؍ 220 M), loss of Fe(III) and U(VI) was first-order at all concentrations tested. Initial reduction rates of all electron acceptors were similar for cells grown with H 2 and sulfate, while cultures grown using lactate and sulfate had similar rates of metal loss but lower sulfate reduction activities. The similarities in metal, but not sulfate, reduction with H 2 and lactate suggest divergent pathways. Respiration assays and reduced minus oxidized spectra were carried out to determine c-type cytochrome involvement in electron acceptor reduction. c-type cytochrome oxidation was immediate with Fe(III) and U(VI) in the presence of H 2 , lactate, or pyruvate.
Progress in bioleaching: fundamentals and mechanisms of bacterial metal sulfide oxidation—part A
Applied Microbiology and Biotechnology, 2013
Bioleaching of metal sulfides is performed by a diverse group of microorganisms. The dissolution chemistry of metal sulfides follows two pathways, which are determined by the mineralogy and the acid solubility of the metal sulfides: the thiosulfate and the polysulfide pathways. Bacterial cells can effect this metal sulfide dissolution via iron(II) ion and sulfur compound oxidation. Thereby, iron(III) ions and protons, the metal sulfide-attacking agents, are available. Cells can be active either in planktonic state or in forming biofilms on the mineral surface; however, the latter is much more efficient in terms of bioleaching kinetics. In the case of Acidithiobacillus ferrooxidans, bacterial exopolymers contain iron(III) ions, each complexed by two uronic acid residues. The resulting positive charge allows an electrostatic attachment to the negatively charged pyrite. Thus, the first function of complexed iron(III) ions is the mediation of cell attachment, while their second function is oxidative dissolution of the metal sulfide, similar to the role of free iron(III) ions in non-contact leaching. In both cases, the electrons extracted from the metal sulfide reduce molecular oxygen via a redox chain forming a supercomplex spanning the periplasmic space and connecting both outer and inner membranes. In this review, we summarize some recent discoveries relevant to leaching bacteria which contribute to a better understanding of these fascinating microorganisms. These include surface science, biochemistry of iron and sulfur metabolism, anaerobic metabolism, and biofilm formation. The study of microbial interactions among multispecies leaching consortia, including cell-to-cell communication mechanisms, must be considered in order to reveal more insights into the biology of bioleaching microorganisms and their potential biotechnological use.
Removal of heavy metals in a flow‐through vertical microbial electrolysis cell
Canadian Journal of Chemical Engineering, 2019
This work describes laboratory experiments aimed at evaluating the feasibility of removing heavy metals from metal-contaminated water in flowthrough microbial electrolysis cells (MECs) with peat moss as a source of organic carbon. MECs were assembled in upflow glass columns containing granular activated carbon (GAC) bioelectrodes preceded by a layer of peat moss. The MECs were fed with metal-contaminated surface water collected at a firing range. At hydraulic retention times (HRT) of 4-6 days, up to 99 % removal of Pb, Zn, Cu, and Fe was observed. The removal efficiency of Zn and Cu declined at an HRT of 1.7 days, while effluent Pb concentration remained below the detection limit for all of the HRTs tested. Metal extraction from MEC compartments showed an accumulation of metals in both the peat moss layer and the GAC cathode, i.e., the removal was achieved by a combination of anaerobic and bioelectrochemical pathways of metal reduction. A proliferation of sulphate reducing bacteria in the peat moss layer and electroactive species in GAC electrodes was confirmed by biomolecular analysis. The proposed flowthrough system, which combines sulphate-reducing and electroactive microbial activities to achieve near-complete metal removal, can be used for removing a broad range of heavy metals from contaminated water in a low-cost passive flow treatment system.
The influence of various ions in the bioleaching of metal sulphides
Hydrometallurgy, 1990
The catalytic effect of various metallic ions (Hg 2 +, Co 2 +, Ag +, Bi 3 + and Cu 2 +) in the bioleaching of a sphalerite concentrate and complex sulphide concentrate was studied. Bacteria of the type ThiobaciUus [erro oxidans adapted to sulphide concentrates were used. The cations studied increase the copper dissolution from complex sulphides, with Ag + and Hg 2 + prominent with an extraction efficiency of 90% and 72.5%, respectively, compared with a 26.5% recovery in the absence of a catalyst. The microbiological dissolution of the sphalerite improves considerably with the addition of Ag + and Cu 2+ as catalysts, with zinc dissolution of 90% Furthermore, it is shown that additional amounts of Cu 2 + increase the percentage of metal leached. The influence of catalytic ions in electrochemical processes of dissolution of complex sulphides is discussed.
pH, Dissolved Oxygen, and Adsorption Effects on Metal Removal in Anaerobic Bioreactors
Journal of Environment Quality, 2003
quently used. These treatment processes can be expensive and inefficient, and generate large quantities of Anaerobic bioreactors were used to test the effect of the pH of wet sludge. influent on the removal efficiency of heavy metals from acid-rock drainage. Two studies used a near-neutral-pH, metal-laden influent One innovative technique for the treatment of acidto examine the heavy metal removal efficiency and hydraulic residence rock drainage has been the use of natural and artificial time requirements of the reactors. Another study used the more typical wetlands as a biological pollution abatement process low-pH mine drainage influent. Experiments also were done to (i) (Dvorak et al., 1992). The self-regenerative properties test the effects of oxygen content of feed water on metal removal and of biological treatment systems have been thought to (ii) the adsorptive capacity of the reactor organic substrate. Analysis reduce the need for continuous maintenance, offering of the results indicates that bacterial sulfate reduction may be a zeroan attractive, alternative abatement technology to the order kinetic reaction relative to sulfate concentrations used in the conventional systems. The biological systems also avoid experiments, and may be the factor that controls the metal mass the production of copious amounts of wet sludge associremoval efficiency in the anaerobic treatment systems. The sorptive ated with oxidative and hydrolytic processes. These pascapacities of the organic substrate used in the experiments had not been exhausted during the experiments as indicated by the loading sive biological systems can also operate at a fraction of rates of removal of metals exceeding the mass production rates of the production and maintenance costs of the convensulfide. Microbial sulfate reduction was less in the reactors receiving tional chemical and physical treatment methods. low-pH influent during experiments with short residence times. Sul-Cohen and Staub (1992), Reynolds (1991), and Mafate-reducing bacteria may have been inhibited by high flows of lowchemer (1992) examined the chemical and biological pH water. Dissolved oxygen content of the feed waters had little processes in wetland treatment systems receiving acidic effect on sulfate reduction and metal removal capacity. drainage and found that the rate of sulfate reduction was the most crucial process involved. The metal-removing characteristics of the natural Engineering, Coolbaugh Hall, Golden, CO 80401.