Microbial degradation of polypropylene microplastics and concomitant polyhydroxybutyrate production: An integrated bioremediation approach with metagenomic insights

The persistence of plastics, particularly polypropylene (PP), and their conversion into microplastics (MPs), specifically PP-MPs, have emerged as serious ecological threats to soil and aquatic environments. In the present study, we aimed to isolate a microbial consortium capable of degrading PP-MPs. The results revealed that three microbial consortia (CPP-KKU1, CPP-KKU2, and CPP-KKU3) exhibited the ability to degrade PP-MPs, achieving weight losses ranging from 11.6 ± 0.2 % to 17.8 ± 0.5 % after 30 days. Fourier transform infrared (FTIR) spectroscopy analysis confirmed the degradation through oxidation, as evidenced by the presence of new functional groups (-OH and -C=O). In particular, CPP-KKU3 showed the highest degradation efficiency, with scanning electron microscopy (SEM) analysis revealing surface cracking after treatment. Additionally, gas chromatography-mass spectrometry (GC-MS) analysis identified various intermediate compounds, including heterocyclic aromatic compounds, phenyl groups, methylthio derivatives, and ethoxycarbonyl derivatives, indicating complex biochemical processes that were likely mediated by microbial enzymes. Furthermore, polyhydroxybutyrate (PHB) production by these consortia was also investigated. The result showed that both CPP-KKU2 and CPP-KKU3 successfully produced PHB, with CPP-KKU3 demonstrating superior performance in terms of PP-MP degradation and PHB production. Metagenomic analysis of CPP-KKU3 revealed abundant carbohydrate-active enzymes (CAZymes), particularly glycosyl transferases and glycoside hydrolases, which are associated with MP digestion. This study presents a promising bioremediation approach that addresses plastic waste degradation and sustainable bioplastic production, offering a potential solution for environmental plastic pollution.