Lignocellulose-mediated selection of halophilic PET-degrading enzymes from mangrove soil

Mangroves are ecosystems located in land-sea transition zones, where they are continuously exposed to plant biomass inputs and plastic pollution. Their soils harbor extensive microbial diversity with potential for discovering polymer-degrading enzymes. Here, we performed a microcosm experiment to examine the responses of mangrove soil microbial communities to inputs of lignocellulose or polyethylene terephthalate (PET) particles in the presence and absence of seawater, and to explore the selection and enrichment of putative PET-active enzymes using gene- and genome-resolved metagenomics. The incubation conditions in the microcosms led to a gradual increase in desiccation and salinity. Consequently, halophilic taxa, including spore-forming bacteria and archaeal species (e.g., Halobacteriales ), were selectively enriched, particularly in seawater-depleted treatments. Lignocellulose input was the main factor restructuring the mangrove soil microbial communities, followed by seawater presence. In dry, lignocellulose-amended microcosms (L treatment), microbial diversity was significantly reduced, while lignocellulolytic species belonging to the phyla Bacillota and Actinomycetota were markedly enriched. Moreover, twelve putative PET hydrolases (PETases) were identified from the L treatment. These proteins shared > 70% sequence similarity with known PET-active enzymes, and three actinobacteria-derived enzymes were predicted to be thermostable, with melting temperatures ranging from 60–67°C. Two predictive PETases belonging to Microbulbifer species displayed distinct sequence and structural features compared to known PET-active enzymes, thereby extending the limited sequence landscape of existing PETases. This study demonstrates the potential of leveraging environmental microbiomes perturbed with plant-derived polymers as a strategy for capturing PETases.