Discovery of Polyesterases from Moss-Associated Microorganisms

The growing pollution of the environment with plastic debris is a global threat, which urgently requires biotechnological solutions. Enzymatic recycling not only prevents pollution but also would allow recovery of valuable building blocks. Therefore, we explored the existence of microbial polyesterases in microbial communities associated with the Sphagnum magellanicum moss, a key species within unexploited bog ecosystems. This resulted in the identification of six novel esterases, which were isolated, cloned, and heterologously expressed in Escherichia coli. The esterases were found to hydrolyze the copolyester poly(butylene adipate-co-butylene terephthalate) (PBAT) and the oligomeric model substrate bis[4-(benzoyloxy)butyl] terephthalate (BaBTaBBa). Two promising polyesterase candidates, EstB3 and EstC7, which clustered in family VIII of bacterial lipolytic enzymes, were purified and characterized using the soluble esterase substrate p-nitrophenyl butyrate (K_m values of 46.5 and 3.4 µM, temperature optima of 48°C and 50°C, and pH optima of 7.0 and 8.5, respectively). In particular, EstC7 showed outstanding activity and a strong preference for hydrolysis of the aromatic ester bond in PBAT. Our study highlights the potential of plant-associated microbiomes from extreme natural ecosystems as a source for novel hydrolytic enzymes hydrolyzing polymeric compounds.