One-Pot Chemobiological Degradation, Bioassimilation, and Upcycling of Waste Poly(lactic acid)

Abstract

Poly(lactic acid) (PLA) is the most widely produced biobased and biodegradable plastic with significant potential to address the plastics sustainability crisis. However, its current lifecycle is typically linear, with the majority of postconsumer PLA entering municipal waste streams or, at best, industrial composting. We hypothesized that the innate biodegradability of PLA and its terminal degradation product, lactate, offers an unexplored opportunity for biological upcycling into industrially valuable chemicals using engineered microbes. Herein, we report an operationally simple and low cost one-pot system for degradation and biological upcycling of waste PLA into the platform chemical protocatechuic acid (PCA). This is enabled by a novel method for PLA hydrolysis in unmodified microbial growth media at neutral pH with moderate heating (90 °C), achieving 85% depolymerization into lactate, showing a previously unreported synergistic mechanism involving phosphate and ammonium chloride. We further demonstrate compatibility with two examples of postconsumer PLA waste, 3D printing waste and food container lids, as well as showing the versatility of this method through degradation of four other biodegradable polyesters. Finally, we show that crude PLA hydrolysate can be directly inoculated with engineered Escherichia coli for bioproduction of PCA, achieving maximum titers of 1.05 mM PCA from authentic 3D printing waste. This study demonstrates, for the first time, that PLA-derived lactate can serve as the sole carbon source for growth and bioproduction using an engineered bacterium, highlighting the potential of biodegradable, next-generation plastic waste as a novel feedstock for chemical biomanufacturing.