Engineered microorganisms can be instrumental in the fight against plastic waste 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 mechanisms to breakdown plastics into molecules that can be recycled by nature. Instead, it can take hundreds of years for some 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 a viable carbon source for bioconversion. In this work, non-conventional yeast were selected against model compounds representative of the composition of thermally oxodegraded High-Density Polyethylene (HDPE), the most common type of plastic. The downselected microorganism grew using depolymerized HDPE as its sole carbon source without needing emulsification, overcoming the mass transfer limitations presented by the 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 powerful microbial cell factory.
