Genomic Insights into a Thermophilic Bacillus licheniformis Strain Capable of Degrading Polyethylene Terephthalate Intermediate

Abstract

Bacillus licheniformis Mb1, a thermophilic strain isolated from the Yungas rainforest innorthwestern Argentina, was analyzed through genomic and experimental approaches toexplore its biotechnological potential. Phylogenomic analysis confirmed its close relationship with B. licheniformis reference strains. The genome revealed multiple genes associatedwith hydrolytic, oxidative, carbohydrate-active, and polyester-degrading activities, indicating a wide enzymatic capacity. Experimental assays demonstrated strong extracellularhydrolytic activities and efficient degradation of bis(2-hydroxyethyl) terephthalate (BHET),a key polyethylene terephthalate (PET) intermediate. In liquid cultures with 3 mg/mLBHET, B. licheniformis Mb1 achieved 99.9% depletion within four days, with transientBHET dimer accumulation and progressive terephthalic acid (TPA) production, reaching1.17 mg/mL after 15 days. Mono (2-hydroxyethyl) terephthalate (MHET) and vanillicacid were not detected. Complete BHET and dimer degradation suggests the presence ofversatile hydrolases acting on short-chain polyester intermediates. Sequence and moleculardocking analyses identified a BHETase-like carboxylesterase as the main enzyme candidate,featuring a truncated lidC region that generates a more open catalytic cleft. This structuraltrait, not previously reported in bacterial BHETases, enables the accommodation of bulkiersubstrates such as BHET dimer. These findings highlight B. licheniformis Mb1 as a promisingbiocatalyst for polyester depolymerization and a valuable microbial resource for futureenzyme discovery and plastic bioremediation strategies.