Metagenomic insights into the synergistic properties and mechanisms of sludge microbial communities degrading polystyrene and polypropylene

Microplastic pollution is a prominent global environmental challenge, with polystyrene (PS) and polypropylene (PP) accumulating over time due to poor degradability, harboring ecological risks. This study used metagenomics to dissect the synergistic characteristics and biodegradation mechanisms of a sludge microbial consortium-enriched from plastic-contaminated industrial activated sludge-with dual-degradation capacity for PS/PP. Bacillota and Pseudomonadota are the dominant phyla, with Bacillus initiating the degradation process and Achromobacter regulating intermediate metabolism, forming an "initiation-metabolism" network. A 60-day experiment revealed direct degradation without pretreatment, with weight loss rates of 13.4 ± 2.3 % for PS microplastics and 23.2 ± 2.4 % for PP microplastics. Multi-dimensional characterization revealed surface disruption, reduced hydrophobicity, and decreased molecular weight in microplastics. PS undergoes benzene ring hydroxylation and carbonylation, producing phenolic and aldehydic metabolites that are then integrated into the tricarboxylic acid (TCA) cycle through aromatic compound degradation pathways, according to analyses using Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). In contrast, PP exhibit a sequential oxidative pathway of "hydroxylation→carbonylation→esterification" through fatty acid degradation mechanisms. Metagenomic annotation confirmed functional complementarity between Bacillus-encoded initial hydrolytic enzymes and Achromobacter-encoded metabolic enzymes, the molecular basis for efficient degradation. This study supports PS/PP microplastic in situ bioremediation and advances understanding of microbial synergistic degradation.