Biological degradation of synthetic polyesters—Enzymes as potential catalysts for polyester recycling

The depolymerization of polymers by enzymes is of great interest for biodegradable plastics, a group of materials which has been developed as an answer to increasing problems in plastics waste management. Polyesters play the dominant role in biodegradable polymers and recently a model of polyester degradation by hydrolyses (lipases) has been published. The chain mobility of the polymer chains proved to be the most relevant factor controlling polyester biodegradability, usually excluding many aromatic polyesters such as PET from biodegradation. Recently a new thermophilic hydrolase (activity optimum at 65 °C) from Thermobifida fusca (TfH) was isolated, characterized and expressed in recombinant Escherichia coli. This enzyme is especially active in degrading polyesters containing aromatic constituents, and exhibits a 65% sequence similarity to a lipase from Streptomyces albus and combines characteristics of lipases and esterases. TfH is even capable to degrade commercial PET from beverage bottles. Specific modification of the active site of enzymes like TfH may open the door for enzymatic PET recycling in the future.