Thermophilic Polypropylene-Degrading Bacteria from Natural Hot Springs: Isolation, Characterization, and Biodegradation Potential

Polypropylene (PP) is one of the most recalcitrant petroleum-based plastics, and its biodegradation under thermophilic conditions is poorly understood. This study isolated a thermophilic bacterial strain, Bacillus licheniformis GSHC01, from geothermal springs in West Java, Indonesia, and evaluated its ability to degrade PP at 60°C. The isolate was initially screened in minimal salt medium (MSM) supplemented with polypropylene glycol (PPG) as the sole carbon source. The selected strain demonstrated growth under these conditions, indicating its potential to utilize PP-related substrates. The degradation ability of the isolate was further assessed by incubating PP films with the isolate for 21 days. The PP films exhibited a mass loss of 7.43 ± 0.03% in MSM and 4.57 ± 0.03% in MSM supplemented with glucose, suggesting a tendency toward enhanced surface modification when PP served as the sole carbon source. Three-dimensional surface analysis revealed substantial increases in roughness parameters (Sa and Sz), with MSM-treated films exhibiting the most severe microstructural damage, including cracks, pits, and erosion zones. Fourier-transform infrared spectroscopy (FTIR) analysis confirmed chemical modifications through the emergence of O–H and C=O functional groups, indicating oxidative chain scission. Gas chromatography–mass spectrometry (GC–MS) detected low-molecular-weight hydrocarbons and ketones, validating PP backbone depolymerization and early-stage biodegradation pathways. These results demonstrate that Bacillus licheniformis strain GSHC01 is capable of initiating surface-limited degradation and early-stage oxidative depolymerization of polypropylene under thermophilic conditions, highlighting the potential of thermophilic microbial systems for environmentally sustainable polypropylene biodegradation.