(354b) Bioconversion of Polyethylene after Thermal Oxo-Degradation As Plastic Upcycling Strategy

Engineered microorganisms can be instrumental in the fight against plastic wastes and for the advancement of a circular economy. Over 8 billion tons of plastics have been produced, and over half of it has ended or will end in landfills or the environment. Plastic accumulates in the environment because evolution has not had enough time to develop a mechanism to break down plastics into molecules that can be recycled by nature. Instead, it can take hundreds of years for plastics to break down via abiotic action, making it the rate-limiting step in plastic biodegradation. Thermal oxo-degradation (TOD) can accelerate this rate-limiting step by rapidly deconstructing the polymer backbone and inserting oxygen functionalities to produce lipids and hydrocarbons. At this point, microorganisms can be employed to convert the carbon that originated from plastic wastes into higher-value products. In this work, non-conventional yeasts were selected against model compounds representative of the composition of thermally oxo-degraded High-Density Polyethylene (HDPE), the most common type of plastic. The down-selected microorganism grew using TOD products from plastics as its sole carbon source without emulsification, overcoming the mass transfer limitations presented by a hydrophobic and solid substrate. The already remarkable growth profile of the microorganism was improved via adaptative laboratory evolution, increasing the growth rate by >200%. This work represents the proof-of-concept for a promising plastic waste upcycling approach and presents a non-conventional yeast with the potential to become a microbial cell factory.