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. 2019 Jun 25:10:1452.
doi: 10.3389/fmicb.2019.01452. eCollection 2019.

Goethite Hinders Azo Dye Bioreduction by Blocking Terminal Reductive Sites on the Outer Membrane of Shewanella decolorationis S12

Gang Zhao  1   2 , Enze Li  1   2 , Jianjun Li  1   2 , Feifei Liu  1   2 , Fei Liu  1   2 , Meiying Xu  1   2
Affiliations

Goethite Hinders Azo Dye Bioreduction by Blocking Terminal Reductive Sites on the Outer Membrane of Shewanella decolorationis S12

Gang Zhao et al. Front Microbiol. .

Abstract

Iron (hydr)oxides are the most ubiquitous Fe(III)-containing minerals in the near-surface environments and can regulate organic pollutant biotransformation by participating in bacterial extracellular electron transfer under anaerobic conditions. Mechanisms described so far are based on their redox properties in bacterial extracellular respiration. Here, we find that goethite, a typical iron (hydr)oxide, inhibits the bioreduction of different polar azo dyes by Shewanella decolorationis S12 not through electron competition, but by the contact of its surface Fe(III) with the bacterial outer surface. Through the combined results of attenuated total reflectance (ATR) Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, and confocal laser scanning microscope, we found that the outer membrane proteins MtrC and OmcA of strain S12 are key binding sites for goethite surface. Meanwhile, they were identified as the important reductive terminals for azo dyes. These results suggest that goethite may block the terminal reductive sites of azo dyes on the bacterial outer membrane to inhibit their bioreduction. This discovered role of goethite in bioreduction provides new insight into the microbial transformation processes of organic pollutants in iron (hydr)oxide-containing environments.

Keywords: Shewanella decolorationis S12; azo dye; bioreduction; goethite; mineral interface.

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Figures

FIGURE 1
FIGURE 1
Biological reduction of methyl orange (A) and methyl red (B) by strain S12. The controls (CK) were prepared under the same conditions but without strain S12 inoculation. The plots are the average of triplicate samples and error bars indicate the standard deviation.
FIGURE 2
FIGURE 2
TEM of S12-goethite aggregations when strain S12 and goethite were pre-equilibrated for 4 h (a); ATR-FTIR spectra of S12 cells on ZnSe and goethite after 4 h equilibrium (b).
FIGURE 3
FIGURE 3
Synchronous (A) and asynchronous (B) contour maps obtained from the time-dependent ATR-FTIR spectra of strain S12 attached on goethite for 4 h equilibration.
FIGURE 4
FIGURE 4
Representative CLSM images of strain S12 (a), S12 (△mtrC) (b), and S12 (△omcA) (c) on goethite-coated glass slides after 4 h. The area of each image is 319.53 μm2. The surface cell density of strain S12, △mtrC, and △omcA was 0.176 ± 0.018, 0.077 ± 0.006, and 0.06 ± 0.005 cells μm–2, respectively.
FIGURE 5
FIGURE 5
ATR-FTIR spectra of strain S12, S12 (△mtrC), and S12 (△omcA) on goethite.
FIGURE 6
FIGURE 6
Schematic representation of the proposed effect mechanisms of goethite on bioreduction of methyl orange and methyl red by S. decolorationis S12.
See this image and copyright information in PMC

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