Microbial integration of plastics in the circular economy

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In this proposal we will develop the technology required to use two recalcitrant plastic polymers, polyethylene terephthalate (PET) and polyurethane (PU) as feedstock for microbial transformations required for a circular economy. In particular, we will focus on the transformation of PET and PU waste into the industrially relevant and more sustainable moieties for Bio-PU polymers. With this approach we will also enable the recycling of the Bio-PU product, completing this way a fully circular strategy for the sustainable production of an important material.The success of PET as a packaging material is only comparable to its resilience to degradation in the environment. Likewise, production rates of PU are also increasing, with the caveat that the recycling procedures for PU are virtually non-existing. PET can be degraded to constituent monomers using physicochemical processes such as pyrolysis and, more recently, by enzymatic hydrolysis. PU, on the other hand, is not so well characterised in terms of enzymatic hydrolysis, but microbial activities against the polymer have been recently described.The synthesis of the monomers required for Bio-PU has been achieved using standard carbon sources (e.g. glucose) in different organisms. In MIPLACE we will synthesise them in biotransformations using the products of hydrolysis of PET as the sole energy and carbon source. Preliminary results from members in the consortium show that this can be achieved although with low yields.Despite their limited scope, these previous observations support that PET and PU are feasible substrates for bacterial growth. In this proposal we will expand on those works and establish PET and PU as general substrates for biotechnological applications including the development of bacterial communities that can directly feed on PET and PU as the sole carbon source without the need of a prior lytic step.In MIPLACE we have devised a multidisciplinary strategy based on the use of microbial communities for the effective transformation of PET and PU into Bio-PU. Our workflow is based on the traditional design-build-test cycle of engineering disciplines. We will use a combination of environmental screening of microorganisms, rational design of strains and lab directed evolution to achieve this goal. We build on the complementary strengths of the partners involved, which include enzymology, synthetic biology, metabolic engineering, mathematical modelling, chemical engineering and biodegradation. At the same time, we will address the societal concerns associated to this research that are related to the public perception of the approach taken and the possibility of influencing changes in consumer behaviour.Overall, MIPLACE will deliver the technological development required for incorporating plastic polymers in the circular economy, paving the way for new biotechnological approaches based on a material that would otherwise be condemned to end up as waste otherwise. By developing efficient microbial PET transformation processes, we aim to use these waste streams in a completely new approach as fossil-based carbon sources for the production of value-added materials, providing the economic incentive to increase end-of-life plastic collection in favour of a sustainable bio-based economy.