Presence Of Anthraquinone-2,6-disulfonate Research Articles

Insight into the model quinone compound AQDS mediated the Mn(II) abiotic oxidation and mineral mineralization on hematite surface under oxic and neutral conditions

Oxidation of Mn(II) and the subsequent mineral mineralization can significantly influence the transport and fate of trace metals and organic pollutants in the soil and sediment environments. Abiotic oxidation of Mn(II) on the surface of Fe mineral in the open air is a vital formation pathway of Mn (oxyhydr)oxides; however, the impact of electron shuttle substances at neutral pH has seldomly been reported. Anthraquinone-2, 6-disulfonate (AQDS) is a typical electron shuttle and might affect the abiotic oxidation of Mn(II). In this study, abiotic oxidation of Mn(II) on the surface of a hematite substrate and mineralization of oxidation product in the presence of AQDS (0–1 mM) were investigated at pH 7.5 in the open air. In the Mn(II)-AQDS treatments, most Mn(II) remained in solution, suggesting that AQDS shows little catalytic activity in the abiotic oxidation of Mn(II) without hematite present. By contrast, Mn(II) was rapidly oxidized, and oxidation rates increased from 4.2 × 10−2 to 8.8 × 10−2 h−1 with increasing AQDS concentration from 0 to 1 mM in the hematite-Mn(II)-AQDS treatments. Abiotic oxidation of Mn(II) produced granular-like Mn3O4, fibrous-like β-MnOOH, and rod-like γ-MnOOH, and no other secondary Fe minerals were found. The proposed mechanism of the AQDS-mediated abiotic oxidation of Mn(II) on a hematite surface is the AQDS serving as an electronic medium with semiconductor hematite as a foreign substrate, promoting electron transfer between oxygen and Mn(II) on its surface. Our results revealed that electron mediators impart crucial control on not only the rate but also the compositions of Mn(II) oxidation product. The findings of this study provide new insights into the geochemical functions of electron shuttles on the dynamics of redox-sensitive elements under oxic and neutral conditions and expand the understanding of interfacial heterogeneous nucleation reactions at the molecular scale.

Effects of biochar/AQDS on As(III)-adsorbed ferrihydrite reduction and arsenic (As) and iron (Fe) transformation: Abiotic and biological conditions

Microbe induced iron (Fe) reduction play an important role in arsenic (As) transformation and the related secondary mineral formation. Meanwhile biochar could react as electron shuttle for this process. Impact of biochar and model electron shuttle anthraquinone-2,6-disulfonate (AQDS) on the chemical/biological iron reduction of As(III)-adsorbed ferrihydrite and the solid-liquid redistribution of As in M1 buffer were studied. Fe reduction results in the release of As adsorbed on ferrihydrite into the solution. Under abiogenic conditions, both biochar and AQDS promoted ferrous production, the chemical oxidation of As(III) and As release. Inoculate with Shewanella oneidensis MR-1, AQDS has greater electronic shuttle function than biochar (with the maximum Fe(II) contents: 154 mg/L > 76.6 mg/L respectively). However, only 12.8 mg/L As was released in the presence of AQDS, which was much lower than that in the presence of biochar (21.6 mg/L), and may be associated with the transformation of As speciation and the formation of secondary minerals. XRD and EDX-SEM confirmed that the As could be fixed by the generated secondary mineral vivianite. The relative contents of vivianite in biological control and AQDS addition were 2.7% and 18.4%, respectively. This study provides information on the transformation and migration of As and Fe with the addition of biochar under anaerobic conditions, which is potential to understand the mechanism of As(III)-contaminated soil remediation.

The catalytic effect of AQDS as an electron shuttle on Mn(II) oxidation to birnessite on ferrihydrite at circumneutral pH

Abstract Birnessite (δ-MnO2) is the most common manganese (Mn) oxide mineral in soils, sediments, and ocean manganese nodules, and it significantly affects the speciation and mobility of trace metals and organic pollutants. Abiotic oxidation of Mn(II) by dissolved O2 is an important birnessite formation pathway, however, it has rarely been reported at neutral pH due to its very slow oxidation kinetics. Anthraquinone-2, 6-disulfonate (AQDS) is an important electron shuttle in biotic systems and might induce birnessite formation by promoting abiotic Mn(II) oxidation. Herein, the effects of AQDS concentration and types of mineral surfaces on 24 mM Mn(II) oxidation were explored at pH 7.0 using macroscopic and spectroscopic analyses. In the absence of AQDS, birnessite cannot form through the abiotic oxidation of 24 mM Mn(II) unless pH ≥ 8.5. In contrast, birnessite rapidly forms at pH 7.0 in the presence of AQDS, which acts as a catalyst. The catalytic effect of AQDS first increases and then decreases with increasing concentration, and as a “shuttle”, the concentration almost remains constant during Mn(II) oxidation. Additionally, in the absence of ferrihydrite or in the presence of montmorillonite, which is an analogous insulating mineral, AQDS shows a weak catalytic effect on Mn(II) oxidation; thus, no birnessite forms. The mechanisms of Mn(II) oxidation promoted by AQDS and ferrihydrite can be described as AQDS acting as an electronic carrier with semiconductor ferrihydrite as a specific channel facilitating electron transfer between Mn(II) and O2 on its surface. This study provides new evidence that AQDS can transfer electrons in abiotic systems as in biotic systems, leading to efficient Mn(II) oxidation and birnessite formation through an abiotic pathway at circumneutral pH in various geological settings.

Electron shuttles alter selenite reduction pathway and redistribute formed Se(0) nanoparticles

The reduction of selenite and formation of selenium nanoparticles tuned by electron shuttles was investigated using Shewanella oneidensis MR-1. Results showed that anthraquinone-2,6-disulfonate (AQDS) and riboflavin profoundly accelerated the reduction of selenite ranging from 0.5 to 5.0mM. Selenite of 2.5mM was completely removed from the solution after 12-h reduction by S. oneidensis MR-1 with OD600 of 0.5. The acceleration heavily depended on extracellular cytochromes OmcA and MtrC and bypassed the fumarate reductase FccA in the periplasm. These results indicated that electron shuttles diverted the selenite reduction from inside to outside cells. Consistently, extracellular formation of Se(0) nanoparticles was observed in the presence of AQDS, which will benefit for the extraction and purification of these nanoparticles. This study indicates that electron shuttles are readily controllable parameter for selenite reduction and biosynthesis of Se(0) nanoparticles.

Accelerated removal of Sudan dye by Shewanella oneidensis MR-1 in the presence of quinones and humic acids

Although there have been many studies on bacterial removal of soluble azo dyes, much less information is available for biological treatment of water-insoluble azo dyes. The few bacterial species capable of removing Sudan dye generally require a long time to remove low concentrations of insoluble dye particles. The present work examined the efficient removal of Sudan I by Shewanella oneidensis MR-1 in the presence of redox mediator. It was found that the microbially reduced anthraquinone-2,6-disulfonate (AQDS) could abiotically reduce Sudan I, indicating the feasibility of microbially-mediated reduction. The addition of 100 μM AQDS and other different quinone compounds led to 4.3-54.7 % increase in removal efficiencies in 22 h. However, adding 5-hydroxy-1,4-naphthoquinone into the system inhibited Sudan I removal. The presence of 10, 50 and 100 μM AQDS stimulated the removal efficiency in 10 h from 26.4 to 42.8, 54.9 and 64.0 %, respectively. The presence of 300 μM AQDS resulted in an eightfold increase in initial removal rate from 0.19 to 1.52 mg h⁻¹ g⁻¹ cell biomass. A linear relationship was observed between the initial removal rates and AQDS concentrations (0-100 μM). Comparison of Michaelis-Menten kinetic constants revealed the advantage of AQDS-mediated removal over direct reduction. Different species of humic acid could also stimulate the removal of Sudan I. Scanning electronic microscopy analysis confirmed the accelerated removal performance in the presence of AQDS. These results provide a potential method for the efficient removal of insoluble Sudan dye.

Microbial reduction of structural iron in interstratified illite‐smectite minerals by a sulfate‐reducing bacterium

Clay minerals are ubiquitous in soils, sediments, and sedimentary rocks and could coexist with sulfate-reducing bacteria (SRB) in anoxic environments, however, the interactions of clay minerals and SRB are not well understood. The objective of this study was to understand the reduction rate and capacity of structural Fe(III) in dioctahedral clay minerals by a mesophilic SRB, Desulfovibrio vulgaris and the potential role in catalyzing smectite illitization. Bioreduction experiments were performed in batch systems, where four different clay minerals (nontronite NAu-2, mixed-layer illite-smectite RAr-1 and ISCz-1, and illite IMt-1) were exposed to D.vulgaris in a non-growth medium with and without anthraquinone-2,6-disulfonate (AQDS) and sulfate. Our results demonstrated that D.vulgaris was able to reduce structural Fe(III) in these clay minerals, and AQDS enhanced the reduction rate and extent. In the presence of AQDS, sulfate had little effect on Fe(III) bioreduction. In the absence of AQDS, sulfate increased the reduction rate and capacity, suggesting that sulfide produced during sulfate reduction reacted with the phyllosilicate Fe(III). The extent of bioreduction of structural Fe(III) in the clay minerals was positively correlated with the percentage of smectite and mineral surface area of these minerals. X-ray diffraction, and scanning and transmission electron microscopy results confirmed formation of illite after bioreduction. These data collectively showed that D.vulgaris could promote smectite illitization through reduction of structural Fe(III) in clay minerals.

Improved volatile fatty acids production from proteins of sewage sludge with anthraquinone-2,6-disulfonate (AQDS) under anaerobic condition

Organic matters in sewage sludge can be converted into volatile fatty acids (VFAs) as renewable carbon sources. This work for the first time applied anthraquinone-2,6-disulfonate (AQDS) for enhancing VFA production from sewage sludge. With 0.066 or 0.33g AQDSg−1 dried solids (DS), the yields for VFAs peak at 403 or 563mgl−1, 1.9- or 2.7-fold to the control. The accumulated VFAs were principally composed of acetate and propionate. The AQDS enhances degradation rates of model proteins (bovine serum albumin), but had little enhancement on that of model polysaccharides (dextrans). The acidification step is proposed the rate-limiting step for VFA production from sewage sludge, in which the AQDS molecules shuttle electrons to accelerate the redox reactions associated with amino acid degradation. Methanogenic activities are inhibited in the presence of AQDS. The AQDS-assisted VFAs are renewable organic carbon sources, although their direct use for anaerobic digestion is not advised.

Removal of Arsenic from Contaminated Soils by Microbial Reduction of Arsenate and Quinone

We investigated bioremediation of As-contaminated soils by reductive dissolution of As using a dissimilatory As(V)-reducing bacterium (DARB), Bacillus selenatarsenatis SF-1. We also examined the effect of anthraquinone-2,6-disulfonate (AQDS), an extracellular electron-shuttling quinone, on the As extraction. When B. selenatarsenatis was incubated with As(V)-laden Al precipitates, no acceleration of As dissolution was observed in the presence of AQDS, even though the microbial reduction of AQDS occurred actively. In contrast, AQDS addition significantly enhanced the reductive dissolution of As and Fe in analogous experiments with As(V)-laden Fe(III) precipitates, whereas As dissolution did not occur in the absence of the As(V) reducer. These results indicate the dissolution of As was accelerated by indirect reduction of solid-phase Fe(III) following microbial AQDS reduction, although As(V) reduction is vital for As extraction. B. selenatarsenatis was able to extract As from two types of industrially contaminated soils through reduction of solid-phase As(V) and Fe(III). The copresence of AQDS with B. selenatarsenatis improved the removal efficiency of As from the contaminated soils, concomitantly releasing Fe(II), suggesting that simultaneous use of DARB and electron-shuttling compounds can be an effective strategy for remediation of As-contaminated soils.

Reductive biotransformation of Fe in shale–limestone saprolite containing Fe(III) oxides and Fe(II)/Fe(III) phyllosilicates

A <2.0-mm fraction of a mineralogically complex subsurface sediment containing goethite and Fe(II)/Fe(III) phyllosilicates was incubated with Shewanella putrefaciens (strain CN32) and lactate at circumneutral pH under anoxic conditions to investigate electron acceptor preference and the nature of the resulting biogenic Fe(II) fraction. Anthraquinone-2,6-disulfonate (AQDS), an electron shuttle, was included in select treatments to enhance bioreduction and subsequent biomineralization. The sediment was highly aggregated and contained two distinct clast populations: (i) a highly weathered one with “sponge-like” internal porosity, large mineral crystallites, and Fe-containing micas, and (ii) a dense, compact one with fine-textured Fe-containing illite and nano-sized goethite, as revealed by various forms of electron microscopic analyses. Approximately 10–15% of the Fe(III) TOT was bioreduced by CN32 over 60 d in media without AQDS, whereas 24% and 35% of the Fe(III) TOT was bioreduced by CN32 after 40 and 95 d in media with AQDS. Little or no Fe 2+, Mn, Si, Al, and Mg were evident in aqueous filtrates after reductive incubation. Mössbauer measurements on the bioreduced sediments indicated that both goethite and phyllosilicate Fe(III) were partly reduced without bacterial preference. Goethite was more extensively reduced in the presence of AQDS whereas phyllosilicate Fe(III) reduction was not influenced by AQDS. Biogenic Fe(II) resulting from phyllosilicate Fe(III) reduction remained in a layer-silicate environment that displayed enhanced solubility in weak acid. The mineralogic nature of the goethite biotransformation product was not determined. Chemical and cryogenic Mössbauer measurements, however, indicated that the transformation product was not siderite, green rust, magnetite, Fe(OH) 2, or Fe(II) adsorbed on phyllosilicate or bacterial surfaces. Several lines of evidence suggested that biogenic Fe(II) existed as surface associated phase on the residual goethite, and/or as a Fe(II)–Al coprecipitate. Sediment aggregation and mineral physical and/or chemical factors were demonstrated to play a major role on the nature and location of the biotransformation reaction and its products.

Microbial reduction of Fe(III) in the Fithian and Muloorina illites: Contrasting extents and rates of bioreduction

AbstractShewanella putrefaciens CN32 reduces Fe(III) within two illites which have different properties: the Fithian bulk fraction and the &lt;0.2 µm fraction of Muloorina. The Fithian illite contained 4.6% (w/w) total Fe, 81% of which was Fe(III). It was dominated by illite with some jarosite (∼32% of the total Fe(III)) and goethite (11% of the total Fe(III)). The Muloorina illite was pure and contained 9.2% Fe, 93% of which was Fe(III). Illite suspensions were buffered at pH 7 and were inoculated with CN32 cells with lactate as the electron donor. Select treatments included anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. Bioproduction of Fe(II) was determined by ferrozine analysis. The unreduced and bioreduced solids were characterized by Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy. The extent of Fe(III) reduction in the bulk Fithian illite was enhanced by the presence of AQDS (73%) with complete reduction of jarosite and goethite and partial reduction of illite. Mössbauer spectroscopy and chemical extraction determined that 21–25% of illite-associated Fe(III) was bioreduced. The extent of bioreduction was less in the absence of AQDS (63%) and only jarosite was completely reduced with partial reduction of goethite and illite. The XRD and TEM data revealed no significant illite dissolution or biogenic minerals, suggesting that illite was reduced in the solid state and biogenic Fe(II) from jarosite and goethite was either released to aqueous solution or adsorbed onto residual solid surfaces. In contrast, only 1% of the structural Fe(III) in Muloorina illite was bioreduced. The difference in the extent and rate of bioreduction between the two illites was probably due to the difference in layer charge and the total structural Fe content between the Fithian illite (0.56 per formula) and Muloorina illite (0.87). There may be other factors contributing to the observed differences, such as expandability, surface area and the arrangements of Fe in the octahedral sheets. The results of this study have important implications for predicting microbe-induced physical and chemical changes of clay minerals in soils and sediments.

Impact of Ferrihydrite and Anthraquinone-2,6-Disulfonate on the Reductive Transformation of 2,4,6-Trinitrotoluene by a Gram-Positive Fermenting Bacterium

Batch studies were conducted to explore differences in the transformation pathways of 2,4,6-trinitrotoluene (TNT) reduction by a Gram-positive fermenting bacterium (Cellulomonas sp. strain ES6) in the presence and absence of ferrihydrite and the electron shuttle anthraquinone-2,6-disulfonate (AQDS). Strain ES6 was capable of TNT and ferrihydrite reduction with increased reduction rates in the presence of AQDS. Hydroxylaminodinitrotoluenes, 2,4-dihydroxylamino-6-nitrotoluene (2,4-DHANT), and tetranitroazoxytoluenes were the major metabolites observed in ferrihydrite- and AQDS-free systems in the presence of pure cell cultures. Ferrihydrite enhanced the production of amino derivatives because of reactions with microbially produced surface-associated Fe(ll). The presence of AQDS in the absence of ferrihydrite promoted the fast initial formation of arylhydroxylamines such as 2,4-DHANT. However, unlike in pure cell systems, these arylhydroxylamines were transformed into several unidentified polar products. When both microbially reduced ferrihydrite and AQDS were present simultaneously, the reduction of TNT was more rapid and complete via pathways thatwould have been difficult to infer solely from single component studies. This study demonstrates the complexity of TNT degradation patterns in model systems where the interactions among bacteria, Fe minerals, and organic matter have a pronounced effect on the degradation pathway of TNT.

Iron(III) reduction and phosphorous solubilization in humid tropical forest soils

Phosphorus is one of the nutrients most commonly limiting net primary production in soils of humid tropical forests, mainly because insoluble Al and Fe phosphates and strong sorption to Fe(III) (hydr)oxides remove P from the bioavailable pool. Recent field studies have suggested, however, that this loss may be balanced by organic P accumulation under a wet moisture regime (>3350 mm annual precipitation). It has been hypothesized that, as the moisture regime changes from dry to mesic to wet, periods of anoxic soil conditions increase in intensity and duration, depleting Fe(III) (hydr)oxides and releasing sorbed P, but also slowing organic matter turnover, thus shifting the repository of soil P from minerals to humus. Almost no quantitative information is available concerning the coupled biogeochemical behavior of Fe and P in highly weathered forest soils that would allow examination of this hypothesis. In this paper, we report a laboratory incubation study of the effects of biotic Fe(III) (hydr)oxide reduction on P solubilization in a humid tropical forest soil (Ultisol) under a wet moisture regime (3000–4000 mm annual rainfall). The objectives of our study were: (1) to quantify Fe(III) reduction and P solubilization processes in a highly weathered forest soil expected to typify the hypothesized mineral dissolution-organic matter accumulation balance; (2) to examine the influence of electron shuttling on these processes using anthraquinone-2,6-disulfonate (AQDS), a well-known surrogate for the semiquinone electron shuttles in humic substances, as an experimental probe; and (3) to characterize the chemical forms of Fe(II) and P produced under anoxic conditions, both with and without AQDS. Two series of short-term incubation experiments were carried out, one without AQDS and another with an initial AQDS concentration of 150 μM. We measured pH, pE, and the production of Fe(II), total Fe [Fe(II) + Fe(III)], inorganic P, total P (inorganic P + organic P), and biogenic gases (CO 2, H 2 and CH 4). The same positive correlation was found between soluble P release and soluble Fe(II) production throughout incubation, implying that reduction of Fe(III) solubilized P. The Fe(II) produced was mainly particulate, evidently due to the formation of Fe(II) solid phases. Thermodynamic calculations indicated that precipitation of siderite and, in the presence of AQDS, vivianite was favored under the anoxic conditions that developed rapidly in the soil suspensions. Inorganic soluble P released during incubation was very small, indicating that the soluble P produced was mainly in organic form, which is consistent with the hypothesis that P accumulates in soil humus. Our net CO 2 production, H 2 consumption, and Fe(II) production data all suggested that reductive dissolution of Fe(III) (hydr)oxides was a terminal electron-accepting process coupled both to H 2 consumption and organic C oxidation by the native population of microorganisms in the soil. Addition of AQDS accelerated the production of Fe(II) and the release of soluble P, while hastening the decline in H 2 gas levels and suppressing CH 4 production. However, throughout incubation, the same quantitative relationships between soluble Fe(II) and P, and between pE and pH, were found, irrespective of AQDS addition. Thus we conclude that, in our soil incubation experiments, added AQDS functioned with the native microbial population solely as an electron shuttle catalyzing Fe(III) reduction. Whether humic substances in the soil also can act as electron shuttles in this way is a matter for future investigation.

Quinone-respiration improves dechlorination of carbon tetrachloride by anaerobic sludge.

The impact of humic acids and the humic model compound, anthraquinone-2,6-disulfonate (AQDS), on the biodegradation of carbon tetrachloride (CT) by anaerobic granular sludge was studied. Addition of both humic acids and AQDS at sub-stoichiometric levels increased the first-order rate of conversion of CT up to 6-fold, leading to an increased production of inorganic chloride, which accounted for 40-50% of the CT initially added. Considerably less dechlorination occurred in sludge incubations lacking humic substances. By comparison, very limited dechlorination occurred in sterile controls with autoclaved sludge. Accumulation of chloroform (1-10%) and dichloromethane (traces) also accounted for the CT converted. The accumulation of a chlorinated ethene, perchloroethylene (up to 9% of added CT), is also reported for the first time as an end-product of CT degradation. A humus-respiring enrichment culture (composed primarily of a Geobacter sp.) derived from the granular sludge also dechlorinated CT, yielding products similar to the AQDS-supplemented granular sludge consortium. The dechlorination of CT by the Geobacter enrichment was dependent on the presence of AQDS or humic acids, which were reduced during the assays. The reduced form of AQDS, anthrahydroquinone-2,6-disulfonate, was shown to cause the chemical reduction of CT when incubated in sterile medium. The results taken as a whole indicate that the formation of reduced humic substances by quinone-respiring microorganisms can contribute to the reductive dechlorination of CT.

Reaction-based modeling of quinone-mediated bacterial iron(III) reduction

This paper presents and validates a new paradigm for modeling complex biogeochemical systems using a diagonalized reaction-based approach. The bioreduction kinetics of hematite (α-Fe 2O 3) by the dissimilatory metal-reducing bacterium (DMRB) Shewanella putrefaciens strain CN32 in the presence of the soluble electron shuttling compound anthraquinone-2,6-disulfonate (AQDS) is used for presentation/validation purposes. Experiments were conducted under nongrowth conditions with H 2 as the electron donor. In the presence of AQDS, both direct biological reduction and indirect chemical reduction of hematite by bioreduced anthrahydroquinone-2,6-disulfonate (AH 2DS) can produce Fe(II). Separate experiments were performed to describe the bioreduction of hematite, bioreduction of AQDS, chemical reduction of hematite by AH 2DS, Fe(II) sorption to hematite, and Fe(II) biosorption to DMRB. The independently determined rate parameters and equilibrium constants were then used to simulate the parallel kinetic reactions of Fe(II) production in the hematite-with-AQDS experiments. Previously determined rate formulations/parameters for the bioreduction of hematite and Fe(II) sorption to hematite were systematically tested by conducting experiments with different initial conditions. As a result, the rate formulation/parameter for hematite bioreduction was not modified, but the rate parameters for Fe(II) sorption to hematite were modified slightly. The hematite bioreduction rate formulation was first-order with respect to hematite ”free“ surface sites and zero-order with respect to DMRB based on experiments conducted with variable concentrations of hematite and DMRB. The AQDS bioreduction rate formulation was first-order with respect to AQDS and first-order with respect to DMRB based on experiments conducted with variable concentrations of AQDS and DMRB. The chemical reduction of hematite by AH 2DS was fast and considered to be an equilibrium reaction. The simulations of hematite-with-AQDS experiments were very sensitive to the equilibrium constant for the hematite-AH 2DS reaction. The model simulated the hematite-with-AQDS experiments well if it was assumed that the ferric oxide “surface” phase was more disordered than pure hematite. This is the first reported study where a diagonalized reaction-based model was used to simulate parallel kinetic reactions based on rate formulations/parameters independently obtained from segregated experiments.