Role of dienelactone hydrolases in PET biodegradation by flavobacteria <i>Maribacter dokdonensis</i> and <i>Arenibacter palladensis</i>

UHH-5R5, forming biofilms on PET foil and releasing µM amounts of terephthalic acid after 5-7 days. Genome sequencing and functional analyses identified two secreted DHLs designated PET93 and PET94 involved in PET degradation. While their predicted active sites and substrate-binding pockets were identical to previously published PETases, both enzymes differed largely in their structural features from known PETases and represent novel scaffolds. Further, they lacked the typical porC domain of the known PETases from the Flavobacteria. Biochemical characterization of the two recombinant enzymes confirmed activity on PET, the primary degradation products Bis(2-Hydroxyethyl) terephthalate (BHET) and Mono-(Hydroxyethyl) terephthalate (MHET). These are the first DLHs identified in the phylum of the Bacteroidota that are hydrolyzing plastics. Our findings indicate that Flavobacteria harbor an unexpectedly wide range of PET-active promiscuous enzymes. IMPORTANCE: Global plastics pollution is a major environmental challenge, and we still have limited knowledge of marine microbiota involved in possible remediation. Our research shows that marine Flavobacteria harbor the potential for PET degradation using dienelactone hydrolases (DLHs, EC 3.1.1.45). The widespread distribution of these microorganisms and the notion that these enzymes are secreted may imply a possible role in marine PET remediation.