Proteomic characterization of Lysinibacillus reveals early-stage PET biodegradation potential

Plastic pollution is a global challenge due to the persistence of synthetic polymers such as polyethylene terephthalate (PET) and the limited efficiency of current recycling strategies. While microbial biodegradation is a promising alternative, the relatively recent introduction of plastics has constrained microbial evolutionary adaptation and enzymatic efficiency. In this study, a PET-associated bacterial strain was isolated from Icelandic soil, identified as Lysinibacillus sp. via 16S rRNA sequencing, and evaluated through growth assays, proteomics, in silico screening, and surface imaging. In mineral medium with PET as the sole carbon source, Lysinibacillus sp. exhibited a shorter lag phase and higher early-stage growth than the reference strain Ideonella sakaiensis ( p < 0.05 at Weeks 1, 2, 4, and 6) over six weeks. FE-SEM revealed microbial colonization, surface erosion, fissures, and delamination, indicating polymer surface alteration. MALDI-TOF MS proteomic analysis did not detect canonical PET-degrading enzymes such as PETase or MHETase. The in silico genome-wide screen similarly failed to identify PETases or other known polyester hydrolases carrying the conserved GXSXG motif, the Ser-His-Asp catalytic triad, or compatible α/β-hydrolase domain architecture. Instead, PET exposure triggered metabolic reprogramming dominated by oxidative-stress response proteins (peroxiredoxins, superoxide dismutases, thiol peroxidases) and central metabolic enzymes. Although several proteins annotated as hydrolases were expressed, these lacked the catalytic signatures and structural features characteristic of validated PET-degrading polyesterases. Taken together, the proteomic and in silico results indicate that Lysinibacillus sp. responds to PET through broad metabolic and oxidative-stress adaptation rather than through expression of dedicated PET-hydrolyzing enzymes. This stress-driven remodeling may support limited transformation of PET-associated compounds but does not constitute evidence of direct PET depolymerization. The rapid adaptive response of Lysinibacillus sp. complements the slower, enzyme-driven strategy of I. sakaiensis , supporting the potential of microbial consortia for multi-stage plastic biodegradation.