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Structure & Reactivity of Biogenic Minerals
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Manganese Oxide Precipitation and Reactivity in Bacterial Flocs
Manganese
oxides, as a class of prevalent secondary minerals, are some of the
most reactive surfaces in soil and marine environments. The
Mn oxidation states of Mn(II), Mn(III), and Mn(IV) are environmentally
relevant. The oxidation of Mn(II)aq by
dissolved oxygen is a thermodynamically favorable reaction in most
natural waters (i.e., pH 5 and greater); however, this reaction is
kinetically sluggish. In most cases, where Mn oxides are forming
rapidly, the oxidation reaction is being catalyzed by microbial
activity. During my dissertation research, I examined Mn
oxidation processes catalyzed by bacterial flocs (extracellular
polymeric substance, EPS, encased aggregates of cells). These
experiments were carried out with Mn oxide formation, structure, and
reactivity in soils and freshwater settings in mind. Through a
combination of spatially-resolved synchrotron-radiation
spectromicroscopy (STXM and Mn L-edge NEXAFS) and bulk kinetic
measurements (reductive dissolution by ascorbic acid), I discovered:
(1) the Mn oxidation process proceeded from Mn(II), to Mn(III) as an
intermediate, and Mn(IV) as a final product, (2) the Mn(IV) oxide
accumulated immediately adjacent to the bacterial cells, (3) the Mn(IV)
oxide was encased in bacterial EPS, (4) the bacterial EPS did not
significantly inhibit the movement of small organic molecules from bulk
solution to the Mn(IV) oxide particles.
This research, and the projects discussed below, were carried out at
the University of California at Berkeley under the advisement of
Garrison Sposito, in collaboration with Bradley Tebo (then Scripps, now
OGI), John Bargar and Samuel Webb (Stanford Synchrotron Radiation
Laboratory), Thomas Spiro (then Princeton, now University of
Washington), Alain Manceau (University of Grenoble), Sirine Fakra and
Matthew Marcus (Advanced Light Source), and with assistance from Mary
Firestone and Donald Herman (UCB).
References:
Toner, B., Fakra, S., Villalobos, M.,
Warwick, T., and Sposito, G. (2005). Spatially resolved
characterization of biogenic manganese oxide production within a
bacterial biofilm. Appl. Environ. Microbiol 71: 1300-1310.
Toner, B. and Sposito, G. (2005). Reductive dissolution of
biogenic manganese oxides in the presence of a hydrated biofilm.
Geomicrobiol. J. 22: 171-180.
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Zinc Complexation by Bacterial Flocs and Biogenic Manganese Oxides
*Under Construction*
References:
Toner, B., Manceau, A., Webb, S. M., and Sposito, G. (2006).
Zinc sorption to biogenic hexagonal-birnessite particles within a
hydrated bacterial biofilm. Geochim. Cosmochim. Acta. 70: 27-43.
Toner,
B., Manceau, A., Marcus, M. A., Millet, D. B., and Sposito, G. (2005).
Zinc sorption by a bacterial biofilm. Environ. Sci. Technol. 39:
8288-8294.
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Mineral Structure of Biogenic Manganese Oxides and Synthetic Analogs
*Under Construction*
References:
Villalobos, M., Toner, B.M., Bargar, J., and Sposito, G.
(2003). Characterization of the manganese oxide produced by
Pseudomonas putida strain MnB1. Geochim. Cosmochim. Acta 67: 2649-2662.
Villalobos,
M., Lanson, B., Manceau, A., Toner, B.M., and Sposito, G. (2006).
Structural model for the biogenic Mn oxide produced by Pseudomonas
putida. Am. Mineral. 91:489-502.
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