Functional Enrichment and Sequence-Based Discovery Identify Promiscuous and Efficient Poly Lactic Acid Degrading Enzymes

The recalcitrance of petroleum-based plastics to recycling has prompted the use of alternative compostable materials such as poly lactic acid (PLA) and polybutylene terephthalate coadipate (PBAT). However, current preferred end-of-life waste management solutions, such as aerobic composting and anaerobic digestion, are not optimal for bioplastics, due to their slow and variable degradation rates. Thus, the isolation of novel microbes and their plastic-degrading enzymes is necessary to improve existing bioplastic disposal and create more sustainable routes to valorize waste plastic. In this study, through functional enrichment cultures, we isolated 14 unique microbes capable of PLA and PBAT degradation and applied a computational discovery pipeline to identify plastic-degrading enzymes. Through this, a focused set of 97 enzymes was functionally characterized, finding three active PLA-degrading enzymes. The two most active enzymes, JW45_1534 and JW44_1708, displayed broad polyester degrading activity against PLA, PBAT, PBSA, PCL, and Impranil polyurethane. Uniquely, under optimized reaction conditions, JW44_1708 fully solubilized low-molecular-weight PLA powder (100-500 mM lactic acid equivalents) in 18 h at 30 °C, with 43-65% conversion to monomeric lactic acid. Overall, we demonstrate the effectiveness of functional enrichment with single-pass computational filtering and screening for finding highly active PLA-degrading enzymes with the potential to improve PLA end-of-life waste management solutions.