scholarly journals Interpretation of kinetic isotope fractionation between aqueous Fe(II) and ferrihydrite under a high degree of microbial reduction

2020 ◽  
Author(s):  
Lei Jiang ◽  
Chuanjun Wu ◽  
Mingqing Li ◽  
Xuegong Li ◽  
Jiwei Li
Keyword(s):  
Isotope Exchange ◽  
Iron Reduction ◽  
Isotope Fractionation ◽  
Shewanella Oneidensis ◽  
Microbial Reduction ◽  
Fractionation Factor ◽  
Terminal Electron Acceptor ◽  
Iron Mineral ◽  
Dissimilatory Iron Reduction ◽  
Kinetic Fractionation

Abstract. Microbial dissimilatory iron reduction (DIR) often ceases when the degree of iron mineral reduction is low, at which point isotope fractionation occurs between an aqueous Fe(II) solution and a reactive Fe(III) phase on the surface of ferric (oxyhydro) oxides, forming an equilibrium fractionation factor (~ 3 ‰). Recent experimental abiotic studies suggest that Fe(II) adsorption onto the mineral surface may affect the isotope fractionation, which reminds us that the isotope exchange may be greatly inhibited during the DIR process. In this study, ferrihydrite is used as a terminal electron acceptor to conduct Shewanella piezotolerans WP3 and Shewanella oneidensis MR-1 experiments at 0.1 and 15 MPa to ensure a significant variation in the degree of reduction. During the 30-day experiment, the degree of ferrihydrite reduction by S. piezotolerans WP3 is 14 % (at 0.1 MPa) and 8 % (at 15 MPa), whereas the degree of ferrihydrite reduction by S. oneidensis MR-1 is 39 % (at 0.1 MPa) and 36 % (at 15 MPa). Based on the isotope mass balance, the estimated ranges of iron isotope fractionation for S. piezotolerans WP3 and S. oneidensis MR-1 are obtained. The former ranges between −3.58 ‰ and −0.88 ‰ (at 0.1 MPa) and between −2.37 ‰ and −0.66 ‰ (at 15 MPa), and the latter ranges between −0.39 ‰ and 0.10 ‰ (at 0.1 MPa) and between −0.6 ‰ and −0.16 ‰ (at 15 MPa). However, it is difficult to distinguish variations in the same bacteria at 0.1 and 15 MPa due to the large estimation ranges of isotope fractionation. In the S. oneidensis MR-1 experiment, the fractionation factor obtained is significantly different from that obtained in the S. piezotolerans WP3 experiment, indicating that kinetic fractionation occurred. In combination with previous studies, we propose a transient modified Fe(II) adsorption mechanism to explain the isotope fractionation between aqueous Fe(II) and ferrihydrite. When the adsorbed Fe(II) exceeds the surface saturation, the atom (isotope) exchange will be suppressed.

scholarly journals Kinetic Characterization of OmcA and MtrC, Terminal Reductases Involved in Respiratory Electron Transfer for Dissimilatory Iron Reduction in Shewanella oneidensis MR-1

2009 ◽  
Vol 75 (16) ◽  
pp. 5218-5226 ◽  
Author(s):  
Daniel E. Ross ◽  
Susan L. Brantley ◽  
Ming Tien
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Rate Constants ◽  
Iron Reduction ◽  
Shewanella Oneidensis ◽  
Transient State ◽  
Whole Cells ◽  
Soluble Iron ◽  
Reactive Iron ◽  
Dissimilatory Iron Reduction

ABSTRACT We have used scaling kinetics and the concept of kinetic competence to elucidate the role of hemeproteins OmcA and MtrC in iron reduction by Shewanella oneidensis MR-1. Second-order rate constants for OmcA and MtrC were determined by single-turnover experiments. For soluble iron species, a stopped-flow apparatus was used, and for the less reactive iron oxide goethite, a conventional spectrophotometer was used to measure rates. Steady-state experiments were performed to obtain molecular rate constants by quantifying the OmcA and MtrC contents of membrane fractions and whole cells by Western blot analysis. For reduction of soluble iron, rates determined from transient-state experiments were able to account for rates obtained from steady-state experiments. However, this was not true with goethite; rate constants determined from transient-state experiments were 100 to 1,000 times slower than those calculated from steady-state experiments with membrane fractions and whole cells. In contrast, addition of flavins to the goethite experiments resulted in rates that were consistent with both transient- and steady-state experiments. Kinetic simulations of steady-state results with kinetic constants obtained from transient-state experiments supported flavin involvement. Therefore, we show for the first time that OmcA and MtrC are kinetically competent to account for catalysis of soluble iron reduction in whole Shewanella cells but are not responsible for electron transfer via direct contact alone with insoluble iron-containing minerals. This work supports the hypothesis that electron shuttles are important participants in the reduction of solid Fe phases by this organism.

scholarly journals Involvement of theShewanella oneidensisDecaheme Cytochrome MtrA in the Periplasmic Stability of the β-Barrel Protein MtrB

2010 ◽  
Vol 77 (4) ◽  
pp. 1520-1523 ◽  
Author(s):  
Marcus Schicklberger ◽  
Clemens Bücking ◽  
Bjoern Schuetz ◽  
Heinrich Heide ◽  
Johannes Gescher
Keyword(s):  
Gene Expression ◽  
Outer Membrane ◽  
Quantitative Pcr ◽  
Protein Complex ◽  
Iron Reduction ◽  
Heterologous Gene Expression ◽  
Shewanella Oneidensis ◽  
Heterologous Gene ◽  
Dissimilatory Iron Reduction ◽  
Membrane Spanning

ABSTRACTTheShewanella oneidensisouter membrane β-barrel protein MtrB is part of a membrane-spanning protein complex (MtrABC) which is necessary for dissimilatory iron reduction. Quantitative PCR, heterologous gene expression, and mutant studies indicated that MtrA is required for periplasmic stability of MtrB. DegP depletion compensated for this MtrA dependence.

scholarly journals Genomic Plasticity Enables a Secondary Electron Transport Pathway in Shewanella oneidensis

2012 ◽  
Vol 79 (4) ◽  
pp. 1150-1159 ◽  
Author(s):  
M. Schicklberger ◽  
G. Sturm ◽  
J. Gescher
Keyword(s):  
Electron Transfer ◽  
Cell Surface ◽  
Outer Membrane ◽  
Iron Reduction ◽  
Shewanella Oneidensis ◽  
Transport Pathway ◽  
Content Type ◽  
Reducing Conditions ◽  
Dissimilatory Iron Reduction ◽  
Membrane Spanning

ABSTRACTMicrobial dissimilatory iron reduction is an important biogeochemical process. It is physiologically challenging because iron occurs in soils and sediments in the form of insoluble minerals such as hematite or ferrihydrite.Shewanella oneidensisMR-1 evolved an extended respiratory chain to the cell surface to reduce iron minerals. Interestingly, the organism evolved a similar strategy for reduction of dimethyl sulfoxide (DMSO), which is reduced at the cell surface as well. It has already been established that electron transfer through the outer membrane is accomplished via a complex in which β-barrel proteins enable interprotein electron transfer between periplasmic oxidoreductases and cell surface-localized terminal reductases. MtrB is the β-barrel protein that is necessary for dissimilatory iron reduction. It forms a complex together with the periplasmic decahemec-type cytochrome MtrA and the outer membrane decahemec-type cytochrome MtrC. Consequently,mtrBdeletion mutants are unable to reduce ferric iron. The data presented here show that this inability can be overcome by a mobile genomic element with the ability to activate the expression of downstream genes and which is inserted within the SO4362 gene of the SO4362-to-SO4357 gene cluster. This cluster carries genes similar tomtrAandmtrBand encoding a putative cell surface DMSO reductase. Expression of SO4359 and SO4360 alone was sufficient to complement not only anmtrBmutant under ferric citrate-reducing conditions but also a mutant that furthermore lacks any outer membrane cytochromes. Hence, the putative complex formed by the SO4359 and SO4360 gene products is capable not only of membrane-spanning electron transfer but also of reducing extracellular electron acceptors.

The Effect of Anharmonic Vibrational Coupling on Deuterium Isotope. Exchange Equilibria Involving Ring Dimers of Carboxylic Acids

1973 ◽  
Vol 28 (2) ◽  
pp. 174-176 ◽  
Author(s):  
E. U. Monse
Keyword(s):  
Isotope Exchange ◽  
Isotope Fractionation ◽  
Hydrogen Gas ◽  
Harmonic Force ◽  
Fractionation Factor ◽  
Vibrational Coupling ◽  
A Value ◽  
Bond Stretching ◽  
Anharmonic Coupling ◽  
Factor Α

The observed isotope fractionation factor, α, for deuterium isotope exchange between liquid acetic acid and hydrogen gas is compared with a value of a calculated on the basis of a harmonic force field for the dimer. The calculated value of a is found to be about 30 % higher than the observed value. The discrepancy is considered to be due to the neglect of anharmonic coupling between the hydroxyl bond stretching- and the hydrogen bond stretching vibrations of the dimer.

Fulvic Acid-Mediated Interfacial Reactions on Exposed Hematite Facets during Dissimilatory Iron Reduction

Langmuir ◽  
2021 ◽  
Author(s):  
Shiwen Hu ◽  
Yundang Wu ◽  
Fangbai Li ◽  
Zhenqing Shi ◽  
Chao Ma ◽  
...  
Keyword(s):  
Fulvic Acid ◽  
Iron Reduction ◽  
Interfacial Reactions ◽  
Dissimilatory Iron Reduction

scholarly journals Measurement on Diffusion Coefficients and Isotope Fractionation Factors by a Through-Diffusion Experiment

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 208
Author(s):  
Takuma Hasegawa ◽  
Kotaro Nakata ◽  
Rhys Gwynne
Keyword(s):  
Groundwater Flow ◽  
Diffusion Coefficients ◽  
Isotope Fractionation ◽  
Free Water ◽  
Effective Porosity ◽  
Diffusion Experiment ◽  
Fractionation Factor ◽  
Through Diffusion ◽  
Geological Formations ◽  
Fractionation Factors

For radioactive waste disposal, it is important that local groundwater flow is slow as groundwater flow is the main transport medium for radioactive nuclides in geological formations. When the groundwater flow is very slow, diffusion is the dominant transport mechanism (diffusion-dominant domain). Key pieces of evidence indicating a diffusion-dominant domain are the separation of components and the fractionation of isotopes by diffusion. To prove this, it is necessary to investigate the different diffusion coefficients for each component and the related stable isotope fractionation factors. Thus, in this study, through-diffusion and effective-porosity experiments were conducted on selected artificial materials and natural rocks. We also undertook measurements relating to the isotope fractionation factors of Cl and Br isotopes for natural samples. For natural rock samples, the diffusion coefficients of water isotopes (HDO and H218O) were three to four times higher than those of monovalent anions (Cl−, Br- and NO3−), and the isotope fractionation factor of 37Cl (1.0017–1.0021) was slightly higher than that of free water. It was experimentally confirmed that the isotope fractionation factor of 81Br was approximately 1.0007–1.0010, which is equivalent to that of free water. The enrichment factor of 81Br was almost half that of 37Cl. The effective porosity ratios of HDO and Cl were slightly different, but the difference was not significant compared to the ratio of their diffusion coefficients. As a result, component separation was dominated by diffusion. For artificial samples, the diffusion coefficients and effective porosities of HDO and Cl were almost the same; it was thus difficult to assess the component separation by diffusion. However, isotope fractionation of Cl and Br was confirmed using a through-diffusion experiment. The results show that HDO and Cl separation and isotope fractionation of Cl and Br can be expected in diffusion-dominant domains in geological formations.

scholarly journals Iron and Carbon Isotope Constraints on the Formation Pathway of Iron-Rich Carbonates within the Dagushan Iron Formation, North China Craton

Minerals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 94
Author(s):  
Xiaoxue Tong ◽  
Kaarel Mänd ◽  
Yuhao Li ◽  
Lianchang Zhang ◽  
Zidong Peng ◽  
...  
Keyword(s):  
Iron Reduction ◽  
Isotope Composition ◽  
Iron Formation ◽  
Banded Iron Formations ◽  
Organic C ◽  
Formation Pathway ◽  
Wide Range ◽  
Dissimilatory Iron Reduction ◽  
O Isotope ◽  
Iron Formations

Banded iron formations (BIFs) are enigmatic chemical sedimentary rocks that chronicle the geochemical and microbial cycling of iron and carbon in the Precambrian. However, the formation pathways of Fe carbonate, namely siderite, remain disputed. Here, we provide photomicrographs, Fe, C and O isotope of siderite, and organic C isotope of the whole rock from the ~2.52 Ga Dagushan BIF in the Anshan area, China, to discuss the origin of siderite. There are small magnetite grains that occur as inclusions within siderite, suggesting a diagenetic origin of the siderite. Moreover, the siderites have a wide range of iron isotope compositions (δ56FeSd) from −0.180‰ to +0.463‰, and a relatively negative C isotope composition (δ13CSd = −6.20‰ to −1.57‰). These results are compatible with the reduction of an Fe(III)-oxyhydroxide precursor to dissolved Fe(II) through microbial dissimilatory iron reduction (DIR) during early diagenesis. Partial reduction of the precursor and possible mixing with seawater Fe(II) could explain the presence of siderite with negative δ56Fe, while sustained reaction of residual Fe(III)-oxyhydroxide could have produced siderite with positive δ56Fe values. Bicarbonate derived from both DIR and seawater may have provided a C source for siderite formation. Our results suggest that microbial respiration played an important role in the formation of siderite in the late Archean Dagushan BIF.

Impact of Graphitic Structures in Pyrogenic Carbon on Microbial Reduction of Ferrihydrite

2021 ◽  
Author(s):  
wentao yu ◽  
baoliang chen
Keyword(s):  
Electron Transfer ◽  
Pyrolysis Temperature ◽  
Shewanella Oneidensis ◽  
Exchange Capacity ◽  
Microbial Reduction ◽  
Systematic Evaluation ◽  
Extracellular Electron Transfer ◽  
Pyrogenic Carbon ◽  
The Impact

<p>Pyrogenic carbon plays important roles in microbial reduction of ferrihydrite by shuttling electrons in the extracellular electron transfer (EET) processes. Despite its importance, a full assessment on the impact of graphitic structures in pyrogenic carbon on microbial reduction of ferrihydrite has not been conducted. This study is a systematic evaluation of microbial ferrihydrite reduction by Shewanella oneidensis MR-1 in the presence of pyrogenic carbon with various graphitization extents. The results showed that the rates and extents of microbial ferrihydrite reduction were significantly enhanced in the presence of pyrogenic carbon, and increased with increasing pyrolysis temperature. Combined spectroscopic and electrochemical analyses suggested that the rate of microbial ferrihydrite reduction were dependent on the electrical conductivity of pyrogenic carbon (i.e., graphitization extent), rather than the electron exchange capacity. The key role of graphitic structures in pyrogenic carbon in mediating EET was further evidenced by larger microbial electrolysis current with pyrogenic carbon prepared at higher pyrolysis temperatures. This study provides new insights into the electron transfer in the pyrogenic carbon-mediated microbial reduction of ferrihydrite.</p>

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