Abstract:Objective To obtain microbial communities capable of degrading polystyrene microplastics (PS) and polypropylene microplastics (PP) and analyze their degradation efficiency and synergistic mechanisms, thus providing resources and theoretical support for the in-situ bioremediation and enriching our understanding of the mechanisms underlying the synergistic degradation of complex pollutants by microbial communities.Methods The microbial communities capable of degrading PS and PP were enriched from plastic-contaminated activated sludge of enterprises. A 60-day degradation experiment was carried out to evaluate the degradation efficiency of the microbial communities on the two microplastics based on the weight loss rate. The surface structures, hydrophobicity, and molecular weight changes of microplastics were characterized by scanning electron microscopy (SEM), water contact angle (WCA), and gel permeation chromatography (GPC). Fourier transform infrared spectroscopy (FTIR) and GC-MS were employed to analyze the degradation products and metabolic pathways of microplastics. The dominant groups, core functional bacteria, and their encoded related enzymes in the microbial communities were clarified through metagenomic analysis, on the basis of which the synergistic degradation mechanisms of the microbial communities were explored.Results The enriched microbial communities were dominated by Bacillota and Pseudomonadota. Bacillus initiated the initial degradation and Achromobacter participated in the intermediate metabolism, forming an “initiation-metabolism” synergistic network. PS and PP could be degraded without pretreatment within 60 days, with weight loss rates of (13.4±2.3)% and (23.2±2.4)%, respectively. Characterization confirmed that the microplastics during degradation presented damaged surfaces, reduced hydrophobicity, and decreased molecular weights. FTIR and GC-MS revealed that PS generated phenols and aldehydes through benzene ring hydroxylation and other processes, and entered the tricarboxylic acid cycle through the aromatic degradation pathway; PP were metabolized through the fatty acid degradation pathway via the oxidation chain of hydroxylation→carbonylation→esterification. The functional annotation of metagenomic data revealed that the genes encoding primary degradative enzymes and metabolic enzymes from Bacillus and Achromobacter exhibited complementary functions, forming the molecular basis for efficient degradation.Conclusion The microbial communities identified in this study efficiently degrade PS and PP. It is hypothesized that their core functional bacteria, Bacillus and Achromobacter, achieve degradation of both microplastics through a synergistic “initiation-metabolism” network and functionally complementary enzyme systems. This provides insights for managing residual microplastics after source control and deepens our understanding of the mechanisms underlying microbial synergistic degradation of complex pollutants.
