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Correlative Cryogenic Spectromicroscopy to Investigate Selenium Bioreduction Products
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posted on 2015-09-15, 00:00 authored by Sirine C. Fakra, Birgit Luef, Cindy J. Castelle, Sean W. Mullin, Kenneth
H. Williams, Matthew A. Marcus, Denise Schichnes, Jillian F. BanfieldAccurate
mapping of the composition and structure of minerals and
associated biological materials is critical in geomicrobiology and
environmental research. Here, we have developed an apparatus that
allows the correlation of cryogenic transmission electron microscopy
(cryo-TEM) and synchrotron hard X-ray microprobe (SHXM) data sets
to precisely determine the distribution, valence state, and structure
of selenium in biofilms sampled from a contaminated aquifer near Rifle,
CO. Results were replicated in the laboratory via anaerobic selenate-reducing
enrichment cultures. 16S rRNA analyses of field-derived biofilm indicated
the dominance of Betaproteobacteria from the Comamonadaceae family
and uncultivated members of the Simplicispira genus. The major product in field and culture-derived biofilms is
∼25–300 nm red amorphous Se0 aggregates of
colloidal nanoparticles. Correlative analyses of the cultures provided
direct evidence for the microbial dissimilatory reduction of Se(VI)
to Se(IV) to Se0. Extended X-ray absorption fine-structure
spectroscopy showed red amorphous Se0 with a first shell
Se–Se interatomic distance of 2.339 ± 0.003 Å. Complementary
scanning transmission X-ray microscopy revealed that these aggregates
are strongly associated with a protein-rich biofilm matrix. These
findings have important implications for predicting the stability
and mobility of Se bioremediation products and understanding of Se
biogeochemical cycling. The approach, involving the correlation of
cryo-SHXM and cryo-TEM data sets from the same specimen area, is broadly
applicable to biological and environmental samples.
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Keywords
Se biogeochemical cyclingCorrelative Cryogenic SpectromicroscopySe bioremediation productscryogenic transmission electron microscopyselenate-reducing enrichment culturesSe 0cryo-TEM data setsÅ.Se 0 aggregatesprotein-rich biofilm matrixExtended X-ray absorption fine-structure spectroscopyInvestigate Selenium Bioreduction ProductsCO16 S rRNA analysesSHXM
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