Choonut_2026_PLoS.One_21_e0341623

This study establishes Paenibacillus naphthalenovorans PETKKU2, isolated from landfill soil in Thailand, as the first reported member of this species capable of degrading polyethylene terephthalate microplastics (PET-MP). Initial screening identified PETKKU2 as the most efficient degrader among ten isolates, achieving 6.07 +/- 0.18% weight loss after 35 days at 37 degreesC. Response surface methodology optimization of pH, nitrogen concentration, and PET-MP loading enhanced degradation to 9.48 +/- 0.21%, closely matching the predicted maximum of 11.15% and representing 96% improvement over baseline conditions. Integrated analytical characterization (FTIR, SEM, GC-MS) revealed an alternative degradation mechanism distinct from classical PETase-MHETase pathways. FTIR analysis confirmed extensive polymer oxidation with 41% reduction in ester carbonyl groups, while SEM demonstrated progressive surface erosion. Critically, the absence of mono(2-hydroxyethyl) terephthalate (MHET) intermediates, combined with whole-genome analysis revealing thermostable lipases, carboxylesterases, and dioxygenases, but no PETase/MHETase homologs, indicates novel enzymatic routes. Operating under mesophilic conditions (37 degreesC), PETKKU2 eliminates energy-intensive heating requirements while achieving performance comparable to established thermophilic degraders. These findings establish a promising platform for sustainable PET-MP bioremediation and advance understanding of alternative microbial plastic degradation mechanisms.