Biodegradation of mixture of plastic films by tailored marine consortia

Summarization: This work sheds light on the physicochemical changes of naturally weathered polymer surfaces along with changes of polymer buoyancy due to biofilm formation and degradation processes. To support the degradation hypothesis, a microcosm experiment was conducted where a mixture of naturally weathered plastic pieces was incubated with an indigenous pelagic community. A series of analyses were employed in order to describe the alteration of the physicochemical characteristics of the polymer (FTIR, SEC and GPC, sinking velocity)as well as the biofilm community (NGS). At the end of phase II, the fraction of double bonds in the surface of microbially treated PE films increased while changes were also observed in the profile of the PS films. The molecular weight of PE pieces increased with incubation time reaching the molecular weight of the virgin pieces (230,000 g mol−1)at month 5 but the buoyancy displayed no difference throughout the experimental period. The number-average molecular weight of PS pieces decreased (33% and 27% in INDG and BIOG treatment respectively), implying chain scission; accelerated (by more than 30%)sinking velocities compared to the initial weathered pieces were also measured for PS films with biofilm on their surface. The orders Rhodobacterales, Oceanospirillales and Burkholderiales dominated the distinct platisphere communities and the genera Bacillus and Pseudonocardia discriminate these assemblages from the planktonic counterpart. The functional analysis predicts overrepresentation of adhesive cells carrying xenobiotic and hydrocarbon degradation genes. Taking these into account, we can suggest that tailored marine consortia have the ability to thrive in the presence of mixtures of plastics and participate in their degradation. Παρουσιάστηκε στο: Journal of Hazardous Material

Biodegradation of weathered polystyrene films in seawater microcosms

A microcosm experiment was conducted at two phases in order to investigate the ability of indigenous consortia alone or bioaugmented to degrade weathered polystyrene (PS) films under simulated marine conditions. Viable populations were developed on PS surfaces in a time dependent way towards convergent biofilm communities, enriched with hydrocarbon and xenobiotics degradation genes. Members of Alphaproteobacteria and Gammaproteobacteria were highly enriched in the acclimated plastic associated assemblages while the abundance of plastic associated genera was significantly increased in the acclimated indigenous communities. Both tailored consortia efficiently reduced the weight of PS films. Concerning the molecular weight distribution, a decrease in the number-average molecular weight of films subjected to microbial treatment was observed. Moreover, alteration in the intensity of functional groups was noticed with Fourier transform infrared spectrophotometry (FTIR) along with signs of bio-erosion on the PS surface. The results suggest that acclimated marine populations are capable of degrading weathered PS pieces

Biomarkers.

<p>Biofilm biomarkers of the initial consortium and the final developed communities. A) LEfSe was used to validate the statistical significance and the effect size of the differential abundances of taxa of INDG community (Kruskal-Wallis and Wilcoxon rank-sum p<0.05 and LDA score >4), B) LEfSe was used to validate the statistical significance and the effect size of the differential abundances of taxa of BIOG community (Kruskal-Wallis and Wilcoxon rank-sum p<0.05 and LDA score >3).</p

Development of tailored indigenous marine consortia for the degradation of naturally weathered polyethylene films

<div><p>This study investigated the potential of bacterial-mediated polyethylene (PE) degradation in a two-phase microcosm experiment. During phase I, naturally weathered PE films were incubated for 6 months with the indigenous marine community alone as well as bioaugmented with strains able to grow in minimal medium with linear low-density polyethylene (LLDPE) as the sole carbon source. At the end of phase I the developed biofilm was harvested and re-inoculated with naturally weathered PE films. Bacteria from both treatments were able to establish an active population on the PE surfaces as the biofilm community developed in a time dependent way. Moreover, a convergence in the composition of these communities was observed towards an efficient PE degrading microbial network, comprising of indigenous species. In acclimated communities, genera affiliated with synthetic (PE) and natural (cellulose) polymer degraders as well as hydrocarbon degrading bacteria were enriched. The acclimated consortia (indigenous and bioaugmented) reduced more efficiently the weight of PE films in comparison to non-acclimated bacteria. The SEM images revealed a dense and compact biofilm layer and signs of bio-erosion on the surface of the films. Rheological results suggest that the polymers after microbial treatment had wider molecular mass distribution and a marginally smaller average molar mass suggesting biodegradation as opposed to abiotic degradation. Modifications on the surface chemistry were observed throughout phase II while the FTIR profiles of microbially treated films at month 6 were similar to the profiles of virgin PE. Taking into account the results, we can suggest that the tailored indigenous marine community represents an efficient consortium for degrading weathered PE plastics.</p></div

SEM analysis.

<p>SEM images of biofilm formed by the marine microbes on polyethylene: (A) at the end of first month, (B) at the end of the phase II and of the surface of the weathered pieces before (C) and after exposure to microbial treatment (D) & (E) at the end of phase II.</p

Microbial communities.

<p>Community composition of major (A) bacterial phyla and classes (B) of the biofilm communities, (C) PCoA plot of the PE adhered communities and (D) <i>alkB</i> gene copy numbers in biofilm communities.</p

Weight reduction of PE films.

<p>A) Percentage of weight reduction by the different marine consortia (A: phase I, B: phase II); B) Percentage of weight reduction of the different polyethylene pieces during the phase II by both treatments.</p

ARISA results.

<p>A) Non-metric multidimensional scaling (nMDS) ordination based on Bray–Curtis similarities from ARISA fingerprints of marine biofilm communities on the polyethylene pieces during the experiment (phase II), B) Shannon–Wiener diversity index among the different PE biofilm communities.</p

Experimental design.

<p>Schematic presentation of A) the experimental sequence; B) incubation and measurements of plastic properties and the microbial community, C) Sample preparation steps for setting up the strings with the plastic pieces, D) growth vessel with labelled strings with weathered plastic pieces of size 1 cm² and biofilm development on plastic pieces.</p

FTIR analysis.

<p>Spectra of virgin LDPE, naturally weathered LDPE, LDPE films exposed to BIOG microbial community for 1 month, LDPE films exposed to BIOG microbial community for 3 months and LDPE exposed to BIOG microbial community for 5 months.</p