Research ArticleENVIRONMENTAL STUDIES

Biodegradation of synthetic polymers in soils: Tracking carbon into CO2 and microbial biomass

See allHide authors and affiliations

Science Advances  25 Jul 2018:
Vol. 4, no. 7, eaas9024
DOI: 10.1126/sciadv.aas9024
  • Fig. 1 Key steps in the biodegradation of polymers in soils.

    Microorganisms colonize the polymer surface and secrete extracellular enzymes that depolymerize the polymer. The formed low–molecular weight hydrolysis products are taken up by the microorganisms and used both for energy production, resulting in the formation of CO2, and for the synthesis of cellular structures and macromolecules, resulting in incorporation of polymer-derived carbon into the microbial biomass. The boxes on the right depict the analytical methods we used to study these steps. NMR, nuclear magnetic resonance.

  • Fig. 2 Mineralization and surface colonization of films of three PBAT [poly(butylene adipate-co-terephthalate)] variants during a 6-week soil incubation.

    (A) Chemical structures of the tested PBAT variants, differing in the monomer unit that was 13C-labeled. PB*AT, P*BAT, and PBA*T contained 1,6-13C2-adipate, 13C4-butanediol, and 1-13C1-terephthalate, respectively. (B) Formation of 13CO2 from the three PBAT variants during their incubation in soil, monitored by 13C isotope-specific CO2 CRDS (cavity ring-down spectroscopy). PBAT variants were added to soils at time = 0 days. Results from replicate experiments performed with a slightly different setup are shown in fig. S1. (C) Representative SEM (scanning electron microscopy) images of a PBAT film after the 6-week soil incubation. The yellow rectangle in the left image defines the area shown at higher magnification in the right image. Scale bars, 50 μm (left) and 5 μm (right).

  • Fig. 3 NanoSIMS (nanoscale secondary ion mass spectrometry) analysis of PBAT films after a 6-week soil incubation.

    See Fig. 2 for details on PBAT variants. Images represent signal intensity distributions of secondary electrons (A), 12C14N ions (B), and the carbon isotope composition displayed as 13C/(12C + 13C) isotope fraction, given in at%. (C) Yellow arrowhead in (A) indicates position of a burrowed hypha. Scale bar in (B) represents 10 μm and applies to all images. (D) Carbon isotope composition within ROI [categorized as background PB*AT, P*BAT, or PBA*T; fungal hyphae (hy); and unicellular organisms (uc) as specified in fig. S10]. Black (solid) dots refer to values obtained from ROI analysis of images shown in (C), and open dots refer to values obtained on replicate films (images shown in fig. S8). Gray rectangles represent the range of apparent 13C contents of microorganisms with natural 13C abundance due to carryover of 13C from the PBAT surface (see text and fig. S9 for details).

  • Fig. 4 NanoSIMS images acquired after extended sputter erosion of the PB*AT film shown also in Fig. 3.

    (A) Distribution of 12C14N ion signal intensity (top) and the 13C content expressed as 13C/(12C + 13C) in at% (bottom). Scale bar, 10 μm. Yellow arrowhead indicates burrowed hypha. (B and D) Line scan analyses 1 (B) and 3 (D) of selected hyphae with respect to 13C content and relative nitrogen content (N/C ratio as inferred from C2 normalized C14N signal intensities; see Materials and Methods for details). The positions of the line scans are shown in (A). (C) Zoom-in of the region indicated by the yellow square (2) in (A). Scale bar, 1 μm. a.u., arbitrary units.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/7/eaas9024/DC1

    Supplementary Materials and Methods

    Fig. S1. Mineralization of PBAT films.

    Fig. S2. NMR analysis of enzymatic hydrolysis products of PBAT films I.

    Fig. S3. NMR spectra of terephthalate, adipate, and butanediol.

    Fig. S4. NMR analysis of enzymatic hydrolysis products of PBAT films II.

    Fig. S5. NMR analysis of enzymatic hydrolysis products of PBAT films III.

    Fig. S6. NMR analysis of enzymatic hydrolysis products of PBAT films IV.

    Fig. S7. Mineralization of terephthalate, adipate, and butanediol.

    Fig. S8. NanoSIMS analysis of PBAT films after soil incubation I.

    Fig. S9. Control experiment for NanoSIMS analysis I.

    Fig. S10. Definition of ROIs.

    Fig. S11. Control experiment for NanoSIMS analysis II.

    Fig. S12. NanoSIMS analysis of PBAT films after soil incubation II.

    Table S1. Soil characterization.

    Table S2. Characterization of PBAT variants.

    Supplementary Appendix. Calculations of the carryover during NanoSIMS measurements.

    References (2933)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • Fig. S1. Mineralization of PBAT films.
    • Fig. S2. NMR analysis of enzymatic hydrolysis products of PBAT films I.
    • Fig. S3. NMR spectra of terephthalate, adipate, and butanediol.
    • Fig. S4. NMR analysis of enzymatic hydrolysis products of PBAT films II.
    • Fig. S5. NMR analysis of enzymatic hydrolysis products of PBAT films III.
    • Fig. S6. NMR analysis of enzymatic hydrolysis products of PBAT films IV.
    • Fig. S7. Mineralization of terephthalate, adipate, and butanediol.
    • Fig. S8. NanoSIMS analysis of PBAT films after soil incubation I.
    • Fig. S9. Control experiment for NanoSIMS analysis I.
    • Fig. S10. Definition of ROIs.
    • Fig. S11. Control experiment for NanoSIMS analysis II.
    • Fig. S12. NanoSIMS analysis of PBAT films after soil incubation II.
    • Table S1. Soil characterization.
    • Table S2. Characterization of PBAT variants.
    • Supplementary Appendix. Calculations of the carryover during NanoSIMS measurements.
    • References (2933)

    Download PDF

    Files in this Data Supplement:

Navigate This Article