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 biodegradable polymers. However, determining the biodegradability of a polymer is not simply a matter of the material property but rather a combination of the polymer chemistry and the environment in which the polymer ends up. One of the largest reservoirs of plastic accumulation is the marine environment due to improper plastic waste management in terrestrial systems contaminating rivers that ultimately lead to the ocean. This work investigates how marine microbial communities with complimentary metabolisms can 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 several 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) using a combination of optical density and CO₂ measurements as a proxy for respiration. From this, a community with complementary metabolisms was selected. These communities were tested for complete mineralization of the polymer via CO₂measurement using cavity ring down spectroscopy (CRDS). Microbes with complementary metabolisms were expected to more rapidly mineralize the polymer to CO₂ than any individual strain on its own. For each consortium, production of monomers into the dissolved organic carbon pool (DOC, i.e., polymeric carbon not fully mineralized to CO₂) was evaluated using liquid chromatography-mass spectrometry (LC-MS). This analysis identifies potentially relevant chemical byproducts (i.e., monomers 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.

Marc Foster

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