Depolymerisation of waste- and bio-based polyesters by an activated sludge hydrolase

This study investigates enzymatic hydrolysis of four novel polyesters (REPolymers) with different structures based on terephthalic acid, ethylene glycol, glutaric acid, and decanediol. These polyesters were synthesized from PET building blocks and bio-based monomers. A hydrolase from Rhizobacter sp. (Rhb), identified from a wastewater treatment sludge metagenome, was used to predict biodegradation and to assess enzymatic recycling potential of the REPolymers. Rhb shows homology to Ideonella sakaiensis PETase but exhibits superior thermostability and activity due to specific amino acids previously identified in PETase engineering. Using mass spectrometry and HPLC-DAD analysis, hydrolysis of REPolymers (5 - 34 kDa) was mechanistically studied. Mono-(2-hydroxyethyl) terephthalic acid (MHET) was the primary product, with longer PET oligomers and aliphatic dimers also detected, indicating endo-wise cleavage of aromatic and aliphatic ester bonds. Consistent degradation patterns showed dimer accumulation across different REPolymers. These findings illuminate how the polyester structure affects enzymatic hydrolysis, supporting the development of novel waste/bio-based polymers and recycling strategies.