Yannick Branson

• This thesis is structured around six interconnected studies that contribute to advancing enzymatic plastic recycling. The first two articles address the development of (ultra-) high-throughput screening methods, introducing a halo formation assay tailored for thermostable polyester hydrolases (Article I) and a growth selection assay for (poly)amidases (Article II). Such advanced screening methods facilitate the discovery of novel (polymer) hydrolases, such as the urethanases identified through metagenomic mining (Article III), which were shown to break down urethane bonds within polymers, as demonstrated in Articles IV and V. In Articles IV and V, structural insights into two of these urethanases, UMG-SP-1 and UMG-SP-2, respectively, were gained by solving their crystal structures, which guided rational enzyme engineering. Finally, Article VI shifted focus to applying these enzymes in a dual-enzyme system for the simultaneous depolymerization of mixed plastics, producing a feedstock suitable for microbial upcycling.