Oceanic Biodegradation Mechanisms of Chemosynthetic Biodegradable Polyesters: Focusing on Poly(butylene succinate-co-adipate)

To address marine plastic pollution, biodegradable plastics have been proposed. However, chemosynthetic biodegradable polyesters exhibit lower marine biodegradability than biosynthetic polyesters, limiting their utility. We elucidated why chemosynthetic polyesters exhibit this lower biodegradability, using an in situ metatranscriptomic approach to identify the microbial communities on the plastics (plastisphere) and enzymes involved in polyester degradation. We compared the oceanic biodegradation rates of three chemosynthetic polyesters, poly(butylene succinate-co-adipate), poly(butylene succinate), and poly(lactic acid), with that of a biosynthetic polyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate). The highest rate was observed in poly(3-hydroxybutyrate-co-3-hydroxyvalerate), whose plastisphere contained many degraders encoding poly(3-hydroxybutyrate) depolymerases. In contrast, two distinct Gammaproteobacteria were dominant and actively transcribed within the poly(butylene succinate-co-adipate) plastispheres; one highly expressed polyesterases for degrading the polyester and the other expressed alcohol and aldehyde dehydrogenases for consuming degradation products. Specific microbial members did not accumulate in the poly(butylene succinate) and poly(lactic acid) plastispheres. Considering the limitation of chemosynthetic polyester degraders in the ocean, effective enrichment of both polyester and monomer degraders will accelerate the biodegradation process via a harmonious metabolic network in the chemosynthetic polyester plastispheres. These findings offer new insights into strategies for enhancing the degradation of chemosynthetic polyesters in marine environments.