Integrated valorization of glycerol and PET into lipids and PHAs using an engineered Yarrowia lipolytica strain and a Pseudomonas-Comamonas consortium

The accumulation of plastic waste necessitates innovative strategies that convert polymer carbon into value-added products. Here, we present a sequential yeast-bacterial workflow for the integrated valorisation of glycerol and amorphous polyethylene terephthalate (amPET) into triacyl glyceride (TAGs) and polyhydroxyalkanoates (PHAs). First, an engineered obese strain of Yarrowia lipolytica was cultivated on glycerol, for the simultaneous production of intracellular lipids, up to 42.9% of its cell dry weight, and secretion of a PET-depolymerizing enzymatic cocktail, composed of the cutinase from Mycothermus thermophilus (HiC) and the lipase B from Moesziomyces antarcticus (CALB). The resulting enzymatic crude hydrolysed amPET, and the released degradation products -terephthalic acid (TPA) and ethylene glycol (EG)- served as feedstocks for a bacterial consortium composed of Comamonas testosteroni RW31 and Pseudomonas putida JM37, which naturally assimilate TPA and EG, respectively. This consortium successfully upcycled the released monomers into intracellular polyhydroxybutyrate (PHB) and medium-chain-length PHAs. Furthermore, fluorescent strains of both bacteria enabled the development of a semi-quantitative method for monitoring the consortium population dynamics. Overall, this study provides a robust proof-of-concept for a circular bioeconomy approach, successfully coupling glycerol-based enzyme and lipid production with the downstream biological conversion of PET-derived monomers into valuable bioplastics.