The plastisphere is a unique ecosystem with microbes colonizing and potentially degrading plastic debris in the environment, provided that the polymers are enzymatically accessible as substrates to drive microbial growth. It also harbors an unusually high occurrence of antibiotic resistance genes, suggesting plastic debris as a potential vector for antibiotic-resistant microorganisms. In this study, we investigated microbial communities in forest soil degrading an emerging type of bioplastics, aliphatic long-chain polyesters (LCAPs). Sequencing analysis revealed a family-VIII esterase strongly associated with LCAP depolymerization that showed high structural similarity to type C β-lactamases. Structural modeling and substrate docking analysis indicated catalytically favorable binding of both LCAP and β-lactam antibiotics. Furthermore, the active site appeared to be located in a large, wide-open groove, rather than in a tunnel, resulting in a protein with a striking "pac-man"-like structure. Heterologous expression and in vitro activity testing confirmed its dual functionality as plastic depolymerase and β-lactam hydrolase. Sequence analysis indicated the enzyme as membrane-associated lipoprotein likely to be directed to the outer membrane. The membrane anchoring of the enzyme may offer striking microbial-ecological benefits, by preventing enzyme loss especially in aqueous environments, by increased catalytic efficiency through high enzyme concentration at the cell-plastic interface, and by spatially linking catalysis with membrane transport, thereby limiting monomer loss to non-producing plastisphere-community members (cheaters). Hence, our study highlighted a plastic depolymerizing enzyme with a striking substrate spectrum, bridging plastics and antibiotics degradation, and provides intriguing perspectives for understanding the microbial physiology, ecology, and evolution of (bio)plastic degradation in the environment.
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