Plastics play important roles in our lives, from food packaging materials to construction. Although plastics are cheaper alternatives to other materials like glass, metals, and wood, they have many adverse effects on the environment. Approximately 4,667 kilotonnes of plastic is introduced in Canadian domestic market annually [1]. Of the total plastic used, of which ~87% ends up in landfills [2]. Reaching a zero plastic waste future will be a challenge. The many benefits of plastics mean they are often not easily replaced by other material, and thus will remain a part of our society for the foreseeable future. While their use can be decreased in some areas, we will in parallel need to develop now technologies for the recycling or upcycling of plastics. As part of the Open Plastic consortium, we are working to develop bio-based recycling technologies to complement mechanical and chemical recycling strategies. In recent years, studies have identified and engineered enzymes that can rapidly breakdown plastic polymers like polyethylene terephthalate (PET) [3-5]. In contrast, enzymatic processes to degrade plastics with carbon-carbon backbones like polyethylene, polystyrene, and PVC are considerably less developed. We are therefore attempting to identify microbes and enzymes able to breakdown these polymers as a first step towards development of bio-technologies for recycling of these plastic.
Degradation of polyethylene, polystyrene, polyvinyl chloride
Polyethylene, polystyrene, and polyvinyl chloride (PVC) have carbon-carbon backbones and thus are more challenging to biodegrade as it is difficult to enzymatically break C-C bonds. However, there is some, albeit inconclusive, evidence suggesting that the gut microbiota of some insect larvae are able to modify these polymers [6]. For example, mealworms (the larvae of Tenebrio molitor beetles) and superworms (the larvae of Zophobas morio beetles), which can be purchased from pet stores as lizard food, will bite and ingest polyethylene, polystyrene, and PVC plastics (see the images to the left); however, whether the plastics simply pass through the insects or are partially digested requires further study. Likewise, other environments contaminated with plastics may harbour microbial communities able to degrade these plastics [7]. To support the development of biotechnologies for the recycling of these plastics, we are using a combination of shotgun metagenomics, microbial isolation, and whole genome sequencing to identify microbes and enzymes able to modify these polymers. Specifically, we aim to:
- Characterize the gut microbial communities of mealworms and superworms fed various types of plastics. Some studies suggest that the gut microbiota of mealworms and superworms can modify plastic polymers [ref]. If true, we hypothesize that microbes capable of degrading plastics will be enriched in the guts mealworms and superworms fed plastics compared to those not given plastics. We are using shotgun metagenomics and metatranscriptomics to study the gut and frass microbial communities of these insects. Microbes enriched in insects fed plastics are prime candidates for further study for genes associated with plastic modification. This is also of interest from a biodiversity perspective, as little is known about the gut microbial communities of these beetle larvae.
- Study the microbial communities of plastic-contaminated environments. We aim to use shotgun metagenomics and metatranscriptomics to characterize natural environments contaminated with plastics to identify microbes enriched in these environments compared to comparable environments lacking plastics.
- Generate a collection of microbial isolates capable of degrading plastics. We are building a collection of bacterial and fungal isolates isolated from mealworm and superworm guts, as well as other plastic-associated environments. These isolates will be screened for an ability to breakdown different plastic polymers, and genomics will be used to understand how they are able to do so.
Degradation of plastic pyrolysis oils
A couple recent studies demonstrated the potential of combining pyrolysis with microbial metabolism to generate a hybrid chemical - biological approach to fully degrading plastic waste [8-9]. To complement our work looking for a fully bio-based method of recycling or upcycling plastic waste, we are undertaking studies to isolate or produce more effective microbial strains for use in pyrolysis - microbial hybrid systems. Specifically, we aim to:
- Isolate new microbial strains capable of catabolizing plastic pyrolysis products. We aim to generate a library of fungal and bacterial strains from natural environments, including the guts of wild caught beetles, and to screen them for their potential to rapidly catabolize the pyrolysis products produced from various types of plastics.
- Engineer microbes for use in hybrid chemical - biological plastic recycling. We hope to use synthetic biology tools to develop microbes with better properties for use in industrial recycling / upcycling of plastics using a combined chemical - microbiological approach.
Funding
Support for this research has been provided by Genome Canada, Ontario Genomics, the Government of Ontario, the Natural Sciences and Engineering Research Council of Canada (NSERC), and Imperial Oil.
[1] Deloitte. (2019) Economic study of the Canadian plastic industry, markets and waste: summary report to Environment and Climate Change Canada. Gatineau, QC. HTML
[2] Environment and Climate Change Canada and Health Canada. (2020) Science assessment of plastic pollution. HTML
[3] Yoshida S, et al. (2016) A bacterium that degrades and assimilates poly(ethylene terephthalate). Science. 351: 1196-1199. HTML
[4] Tournier V, et al. (2020) An engineered PET depolymerase to break down and recycle plastic bottles. Nature. 580: 216–219. HTML
[5] Lu H, et al. (2022) Machine learning-aided engineering of hydrolases for PET depolymerization. Nature. 604: 662–667. HTML
[6] Sachez-Hernandez JC. (2021) A toxicological perspective of plastic biodegradation by insect larvae. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology. 248: 109117. HTML
[7] Taipale SJ, et al. (2022) Biodegradation of microplastic in freshwaters: A long‐lasting process affected by the lake microbiome. Environmental Microbiology. 1-12. HTML
[8] Mihreteab M, et al. (2021) Enhancing polypropylene bioconversion and lipogenesis by Yarrowia lipolytica using a chemical/biological hybrid process. Journal of Biotechnology. 332: 94-102. HTML
[9] Byrne E, et al. (2022) Pyrolysis-Aided Microbial Biodegradation of High-Density Polyethylene Plastic by Environmental Inocula Enrichment Cultures. ACS Sustainable Chemistry & Engineering. 10: 2022-2033. HTML
[2] Environment and Climate Change Canada and Health Canada. (2020) Science assessment of plastic pollution. HTML
[3] Yoshida S, et al. (2016) A bacterium that degrades and assimilates poly(ethylene terephthalate). Science. 351: 1196-1199. HTML
[4] Tournier V, et al. (2020) An engineered PET depolymerase to break down and recycle plastic bottles. Nature. 580: 216–219. HTML
[5] Lu H, et al. (2022) Machine learning-aided engineering of hydrolases for PET depolymerization. Nature. 604: 662–667. HTML
[6] Sachez-Hernandez JC. (2021) A toxicological perspective of plastic biodegradation by insect larvae. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology. 248: 109117. HTML
[7] Taipale SJ, et al. (2022) Biodegradation of microplastic in freshwaters: A long‐lasting process affected by the lake microbiome. Environmental Microbiology. 1-12. HTML
[8] Mihreteab M, et al. (2021) Enhancing polypropylene bioconversion and lipogenesis by Yarrowia lipolytica using a chemical/biological hybrid process. Journal of Biotechnology. 332: 94-102. HTML
[9] Byrne E, et al. (2022) Pyrolysis-Aided Microbial Biodegradation of High-Density Polyethylene Plastic by Environmental Inocula Enrichment Cultures. ACS Sustainable Chemistry & Engineering. 10: 2022-2033. HTML