Research ArticleAPPLIED SCIENCES AND ENGINEERING

Extracellular polymeric substances are transient media for microbial extracellular electron transfer

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Science Advances  05 Jul 2017:
Vol. 3, no. 7, e1700623
DOI: 10.1126/sciadv.1700623
  • Fig. 1 Representation of microbial EET mechanisms when a microorganism is working as an electron donor.

    (A) A view of previous studies with proposed direct and indirect microbial EET mechanisms. (B) Can EET processes be affected when EPS cover the cell surface? ETMs, electron transfer mediators.

  • Fig. 2 EPS efficiently removed from MR-1 cells.

    (A) Sphere determination shows a size decrease in MR-1 cells after EPS extraction. (B) AFM image showing that MR-1 cells in the control group are enveloped by EPS. (C) AFM image showing a smooth MR-1 cell surface after EPS extraction. The insets in (B) and (C) enlarge the dashed boxes. Scale bars in (B) and (C), 2 μm.

  • Fig. 3 Electrochemical analysis of MR-1 cells and their EPS.

    (A) DPV of MR-1 cells in the presence of EPS treated at 30°C (blue line) and absence of EPS treated at 38°C (red line). (B) DPV of EPS extracted from MR-1 by heating at 38°C.

  • Fig. 4 Integrity tests on MR-1 cells.

    (A and B) Flow cytometry shows that EPS extraction only destroys insignificantly the MR-1 cells. (A) Flow cytometry of MR-1 cells treated at 30°C. (B) Flow cytometric analysis of MR-1 cells treated at 38°C for EPS extraction. Green and red spots are living and dead cells, respectively. (C and D) LIVE/DEAD staining of MR-1 cells shows similar ratios of live cells to total MR-1 cells in the presence (C) and absence (D) of EPS. (E) The concentration of NAG in EPS extracted at different temperatures. (F) The ETSA of MR-1 cells after EPS extraction at different temperatures. Samples in all experiments at different temperatures are heat-treated for 30 min.

  • Fig. 5 Schematic of EPS as transient media for microbial EET by electron hopping.
  • Fig. 6 DPV of cells and EPS of WS-XY1 and Ps.

    (A and B) DPV of WS-XY1 (A) and Ps (B) cells in the presence and absence of EPS. (C and D) DPV of EPS extract from WS-XY1 (C) and Ps (D) strains.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/7/e1700623/DC1

    Supplementary Discussion

    fig. S1. 3D AFM images of S. oneidensis MR-1 cells.

    fig. S2. Yields of different EPS components from MR-1.

    fig. S3. CV of S. oneidensis MR-1 cells in the presence (blue line) and absence (red line) of EPS.

    fig. S4. UV-vis spectra of EPS from MR-1.

    fig. S5. Chronoamperometry i-t test on MR-1 cells.

    fig. S6. DPV curves for MR-1 cell pellets treated at 30° and 38°C.

    fig. S7. DPV curves for MR-1 cell culture treated at 30° and 38°C.

    fig. S8. Effect of different heating temperatures on microbial viability evaluated by flow cytometry.

    fig. S9. Yields of different EPS components from strains WS-XY1 and Ps.

    fig. S10. Live/Dead staining of WS-XY1 and Ps cells after heating treatments.

    fig. S11. CV of pure and EPS-depleted cells of WS-XY1 and Ps.

    table S1. Size determination of MR-1 cells using a laser particle size analyzer.

    table S2. Amperometric i-t test for MR-1 cells.

    table S3. Charge calculation based on DPV shown in Fig. 3.

    References (3942)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Discussion
    • fig. S1. 3D AFM images of S. oneidensis MR-1 cells.
    • fig. S2. Yields of different EPS components from MR-1.
    • fig. S3. CV of S. oneidensis MR-1 cells in the presence (blue line) and absence (red line) of EPS.
    • fig. S4. UV-vis spectra of EPS from MR-1.
    • fig. S5. Chronoamperometry i-t test on MR-1 cells.
    • fig. S6. DPV curves for MR-1 cell pellets treated at 30° and 38°C.
    • fig. S7. DPV curves for MR-1 cell culture treated at 30° and 38°C.
    • fig. S8. Effect of different heating temperatures on microbial viability evaluated by flow cytometry.
    • fig. S9. Yields of different EPS components from strains WS-XY1 and Ps strains.
    • fig. S10. Live/Dead staining of WS-XY1 and Ps cells after heating treatments.
    • fig. S11. CV of pure and EPS-depleted cells of WS-XY1 and Ps.
    • table S1. Size determination of MR-1 cells using a laser particle size analyzer.
    • table S2. Amperometric i-t test for MR-1 cells.
    • table S3. Charge calculation based on DPV shown in Fig. 3.
    • References (39–42)

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