Formation of manganese oxides by bacterially generated superoxide

Learman, Deric R.; Voelker, Bettina M.; Vazquez-Rodriguez, A. I.; Hansel, Colleen M.

doi:10.1038/ngeo1055

Cited by 322 publications

(273 citation statements)

References 27 publications

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“…Metal oxide surfaces are able to accelerate Mn(II) oxidation by O 2 . Examples are provided by hematite and manganese dioxide (32); lepidocrocite (33); goethite, lepidocrocite, and alumina (34); and colloidal hexagonal birnessite (35). The present study suggests that these reactions will be affected or perhaps even thermodynamically driven by both particle size and degree of hydration and that the equilibria can respond rapidly to changes in water availability.…”

Section: Discussion: Geochemical and Technological Implicationsmentioning

confidence: 97%

Rapidly reversible redox transformation in nanophase manganese oxides at room temperature triggered by changes in hydration

Birkner

Navrotsky

2014

Proc. Natl. Acad. Sci. U.S.A.

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Chemisorption of water onto anhydrous nanophase manganese oxide surfaces promotes rapidly reversible redox phase changes as confirmed by calorimetry, X-ray diffraction, and titration for manganese average oxidation state. Surface reduction of bixbyite (Mn 2 O 3 ) to hausmannite (Mn 3 O 4 ) occurs in nanoparticles under conditions where no such reactions are seen or expected on grounds of bulk thermodynamics in coarse-grained materials. Additionally, transformation does not occur on nanosurfaces passivated by at least 2% coverage of what is likely an amorphous manganese oxide layer. The transformation is due to thermodynamic control arising from differences in surface energies of the two phases (Mn 2 O 3 and Mn 3 O 4 ) under wet and dry conditions. Such reversible and rapid transformation near room temperature may affect the behavior of manganese oxides in technological applications and in geologic and environmental settings.phase transformation | oxidation/reduction | water adsorption/desorption M anganese oxides are ubiquitous in the natural environment, often occurring as very fine grained (nanopahase) precipitates and coatings, and also find numerous technological applications, especially in catalysis. Easy variation of manganese oxidation state (Mn 2+ , Mn 3+ , Mn 4+ ) lends complexity to phase behavior and physical and chemical properties of manganese oxides. The thermodynamic stability of manganese oxide nanoparticles helps determine the robustness of such oxides and their behavior in soils and larger-scale geochemical cycles, as well as in applications in catalysis, renewable energy, and environmental remediation. The structure and energetics of nanoparticle surfaces are influenced by the phase present and its oxidation state and by the extent of surface hydration; thus dry surfaces are structurally and thermodynamically distinct from hydrated surfaces (1, 2). Using Mn 3 O 4 (hausmannite), Mn 2 O 3 (bixbyite), and MnO 2 (pyrolusite), previously, we showed that the position in temperature−oxygen fugacity space, of oxidation−reduction (redox) phase equilibria, is shifted at the nanoscale due to differences in nanophase surface energy as a function of particle size and surface hydration and that this thermodynamic shift is in favor of the lower surface energy phase (3). In the manganese oxides, the surface energy increases in the order hausmannite, bixbyite, pyrolusite, so small particle size favors the more reduced oxide phase.This paper summarizes observations in the nanoscale Mn 2 O 3 − Mn 3 O 4 system, which is found to undergo rapidly reversible redox phase transformations at room temperature induced by the adsorption/desorption of surface water. It is expected that the degree of reduction is a function of both average particle size and particle size distribution, but this work focuses on only one representative material to provide proof of concept. The rapid response of activated surfaces to changing hydration condition implies thermodynamic control and has implications for geochemistry, planetary scie...

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Section: Discussion: Geochemical and Technological Implicationsmentioning

confidence: 97%

Rapidly reversible redox transformation in nanophase manganese oxides at room temperature triggered by changes in hydration

Birkner

Navrotsky

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…It was reported that superoxide can be produced by bacteria and fungi. [19][20][21]23,24 Here, for the first time, we demonstrated the production of superoxide by F. oxysporum by using continuous flow CL (Figure 2). No CL signal was observed when only F.…”

Section: Environmental Science and Technology Lettersmentioning

confidence: 99%

“…As the antibacterial activities of AgNPs are much lower than that of Ag + , 50 this bioreduction is also a possible natural antidote to mitigate the toxicity of silver to organisms. Considering the key roles of superoxide in the redox cycles of Fe, 23,51 Mn, 20,21 Cu, 32,52,53 Cr, 54,55 As, 56,57 and I, 22 it is expected that the superoxide-produced organisms should also have great impacts on the biogeochemical cycles of these elements. …”

Section: Environmental Science and Technology Lettersmentioning

confidence: 99%

“…Cu 2+ is an effective and rapid superoxide scavenger, while chemically similar Zn 2+ cannot catalyze the dismutation of superoxide. 20,21,31 The effect of Cu 2+ (as a superoxide scavenger) and Zn 2+ (as a control) on the formation of AgNPs by F. oxysporum was therefore investigated ( Figure 3A). The addition of Cu 2+ can induce a concentration-dependent inhibition of AgNP formation, suggesting a critical role of superoxide as the reductant of Ag + .…”

Section: Environmental Science and Technology Lettersmentioning

confidence: 99%

“…Recently, it has been demonstrated that bacteria and fungi can produce superoxide, 19,20 which can further mediate the oxidation of Mn(II) 20,21 and I − , 22 and the reduction of Fe(III). 23,24 As demonstrated previously, superoxide produced from KO 2 25,26 or photoirradiated natural organic matter 27 can also reduce Ag + into AgNPs.…”

Section: ■ Introductionmentioning

confidence: 99%

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Superoxide-Mediated Extracellular Biosynthesis of Silver Nanoparticles by the Fungus Fusarium oxysporum

Yin

Xiao-ya

et al. 2016

Environ. Sci. Technol. Lett.

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The biosynthesis of silver nanoparticles (AgNPs) by microorganisms has become a hot topic in recent years, although its mechanism is still not well understood. Here we report the extracellular biosynthesis of AgNPs by the fungus Fusarium oxysporum through a superoxide-dependent mechanism. Reduction of Ag + to AgNPs in the extracellular region of F. oxysporum was verified by transmission electron microscopy, while the superoxide produced extracellularly by F. oxysporum was evidenced by chemiluminescence. We further demonstrated that the biosynthesis of AgNPs was inhibited by a superoxide scavenger or the inhibitor of NADH oxidases, and the addition of NADH significantly improved the formation of AgNPs. These results demonstrated that, for the first time, the fungus F. oxysporum can mediate the synthesis of AgNPs through the enzymatic generation of extracellular superoxide, which is helpful in understanding the biosynthesis of AgNPs and the biomineralization and transformation of silver and other metals or metalloids.

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Manganese Cycling in the Oceans

Tebo

Luther

2019

Encyclopedia of Water

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Manganese (Mn) is an essential element for life. Although its concentration is at (sub)nanomolar levels throughout the ocean, it affects the oxygen concentration of the ocean because it is central to the photosynthetic formation of dioxygen, O 2 , in photosystem center II. Mn inputs into the ocean are from atmospheric transport of particles and their dissolution to form dissolved Mn, and from the flux of dissolved Mn from rivers, sediments, and hydrothermal vents. The main removal mechanism is transport of particulate Mn from dust and organic matter to the sediments. The environmental chemistry of manganese centers on its +2, +3, and +4 oxidation states. Most recent data show that Mn(II) is dissolved, that Mn(IV) is particulate MnO 2 , and that Mn(III) can be particulate or dissolved when bound to organic complexes [denoted as Mn(III)‐L]. Mn(II) is oxidized primarily by microbial processes whereas MnO 2 is reduced by abiotic and biotic processes. Photochemical processing aids redox cycling in surface waters. In suboxic zones, which are defined as areas where both dissolved O 2 and H 2 S concentrations are below 3 μM, both oxidation and reduction processes can occur but usually at different depths. In suboxic zones, dissolved Mn is also released from organic matter during its decomposition and from MnO 2 reduction.

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Formation of manganese oxides by bacterially generated superoxide

Cited by 322 publications

References 27 publications

Rapidly reversible redox transformation in nanophase manganese oxides at room temperature triggered by changes in hydration

Rapidly reversible redox transformation in nanophase manganese oxides at room temperature triggered by changes in hydration

Superoxide-Mediated Extracellular Biosynthesis of Silver Nanoparticles by the Fungus Fusarium oxysporum

Manganese Cycling in the Oceans

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