Polyethylene plastics are a major source of industrial and household wastes, the majority of which end up in the environment or in landfills. These wastes pose challenges for microbial biodegradation due to their polymeric structure. There is a critical need for a process that aids in the breakdown and reuse of plastic compounds. Pyrolysis of high-density polyethylene (HDPE) has previously been used to induce chemical changes in plastic compounds, resulting in more structurally simplistic compounds. Here, we demonstrate the ability of pyrolysis to produce microbially biodegradable intermediate compounds. Biodegradation of pyrolysis-treated plastics has not previously been demonstrated. We found that enrichment cultures derived from six different environmental inocula were able to achieve extensive biodegradation of polyethylene pyrolysis products over the course of 5 days. We verified the biodegradation by quantifying residual compound concentrations of alkenes using gas chromatography/mass spectrometry (GC/MS). 16S rRNA gene amplicon sequencing results demonstrated that the most dominant taxa in the microbial community belonged to the phylum Proteobacteria. Many organisms in this phylum have previously been shown to metabolize hydrocarbons. Our results indicate that the coupling of chemical and biological processes can speed up the breakdown and conversion of polyethylene to bacterial biomass by microbial consortia.

Most plastic waste accumulates in landfills or the environment. Natural microbial metabolisms can degrade plastic polymers. Unfortunately, biodegradation of plastics is slow even under ideal conditions; depolymerization of plastic is the rate limiting step. Rapid chemical depolymerization yields biodegradable plastic monomers, improving biodegradation rates. Here we demonstrate that ammonium hydroxide depolymerizes PET into terephthalic acid and terephthalic acid monoamide which are rapidly metabolized by diverse consortia obtained from compost and sediment. By neutralizing the product with phosphoric acid prior to bioprocessing, the final product contains plastic-derived carbon and biologically accessible nitrogen and phosphorus from the process reactants, removing the need for culture medium. Three microbial consortia were able to degrade chemically deconstructed PET in ultrapure water and scavenged river water without the addition of nutrients, with no statistically significant difference in growth rate compared to communities grown on deconstructed PET in Bushnell Haas minimal culture medium. The consortia were dominated by Rhodococcus spp., Hydrogenophaga spp., and many lower abundance genera. All taxa were related to species known to degrade aromatic compounds. Microbial consortia are known to confer flexibility in processing diverse substrates. To highlight the versatility of these consortia, we also demonstrate that two microbial consortia can grow on similarly deconstructed polyesters, polyamides, and polyurethanes in water instead of medium. Our findings suggest that using microbial communities enable flexible bioprocessing of mixed plastic wastes. We also demonstrate the flexibility of this approach for coupled chemical deconstruction and bioprocessing.

No abstract

Excess plastic waste poses a major environmental problem. Microorganisms can metabolize many of the breakdown products (alkenes) of plastics.