Fig. 1

Synthetic PETtrophy in relation to other biocatalytic strategies for PET waste valorization. Top panel: PET waste can be depolymerized to TA and EG using chemical means (1), with purified PET hydrolases (2), or using whole-cell biocatalysts displaying or secreting PET hydrolases (3) (note: potential PET depolymerization intermediates bis(2-hydroxyethyl) terephthalate (BHET) and mono(2-hydroxyethyl) terephthalate (MHET) are omitted for clarity). TA and EG can be extracted and processed into new virgin PET (A); used as feedstocks for engineered microbes and production of value-added bioproducts (B); or used as feedstocks for engineered microbes producing PET hydrolases in a continuous bioprocessing-like one-pot system (C). Path 2-A was explored by Tournier et al. [19] and Lu et al. [21]; path 1-B was explored by Kenny et al. [22, 94], Werner et al. [24] and Kim et al.; [25] path 2-B was described by Tiso et al. [23] and Lu et al. [21]; path 3-C is what I. sakaiensis perfoms natively [26] and was explored in this study. Additionally, several recent studies described whole-cell biocatalysts displaying or secreting PET hydrolases (3) without attempting downstream extraction or microbial utilization of released monomers. [59, 76,77,78,79,80,81,82,83] Bottom panel: sequence of engineering steps attempted in this study. First, we installed TA, EG or BD metabolism in P. putida using genetic engineering and adaptive laboratory evolution (I); secondly, we tested a variety of expression systems for PET hydrolases (II); third, we attempted to combine these efforts to obtain a self-sustaining whole-cell PET or PBAT depolymerization system (III). Enzyme structure PDB 5xjh. [95]