Fossil fuel-derived plastic materials have a high resistance towards degradation and so accumulate in the environment impacting the health of both terrestrial and marine ecosystems. An alternative for these commercially important materials are biopolymers and polymers that exhibit similar physical properties but could be more prone to degradation. Two challenges in scaling these types of polymers include (1) accurately understanding their fate in the environment in order to quantify the scope of their benefit and (2) finding ways to efficiently recycle plastic waste to resupply chemical feedstocks, lowering the overall cost of the material and closing the lifecycle loop. This work investigates how marine microbial communities with complimentary metabolisms can efficiently degrade plastic materials. Further, the degradation products and pathways may inform novel recycling strategies to return these polymers to chemicals useful to industry. In collaboration with a major chemical company, sheets of the polymer poly(butylene-sebacate–co–terephthalate) (PBSeT) were incubated in Mediterranean seawater over the period of months. From these incubations, individual bacterial strains were cultured and isolated as candidates for potential degradation of PBSeT. These strains were tested for their growth on the whole polymer and the individual monomer units (the expected breakdown products) by measuring optical density. From this, a community with complementary metabolisms was selected. These communities were tested for complete mineralization of the polymer via CO2 measurement using gas chromatography. Microbes with complementary metabolisms were expected to more rapidly mineralize the polymer to CO2 than any individual strain on its own. For each consortium, chemical transformations of resultant dissolved organic carbon (DOC; i.e., the polymeric carbon not fully mineralized to CO2) was evaluated using liquid chromatography-mass spectrometry (LC-MS) to identify potentially relevant chemical byproducts (i.e., for industrial recycle) and to inform biotransformation pathways taking place in nature. Ultimately, this work informs the limitations and opportunities for microbial communities to efficiently degrade the PBSeT polymer and explores the potential for microbially-mediated recycling to useful starting materials for novel chemical synthesis.

Engineering of microbial consortia to investigate degradation pathways and recycling of plastics

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ACS Spring 2023

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