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Molecular mechanism of anammox granular sludge disintegration caused by polyethylene terephthalate micro/nanoplastics: a new perspective based on quorum sensing
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Tiny plastic particles from PET plastic (the kind used in water bottles) can break down the beneficial bacteria communities that wastewater treatment plants rely on to remove harmful nitrogen compounds, by disrupting the chemical signals bacteria use to "talk" to each other and stick together. This matters because as microplastic pollution increases, it could weaken our ability to properly treat wastewater, potentially allowing more nitrogen pollution and untreated contaminants to reach our water supplies and environment.
Quorum sensing (QS) regulates the synthesis and secretion of extracellular polymeric substances (EPS), which are essential for maintaining the structural stability of anaerobic ammonium oxidation (Anammox) granular sludge. However, the molecular mechanism linking polyethylene terephthalate micro/nanoplastics (PET-MNPs)-induced QS disruption to EPS inhibition remains unclear. This study investigated the effects of two PET-MNP sizes (80 μm and 300 nm) on Anammox granular sludge under different exposure concentrations. PET-MNPs significantly reduced nitrogen removal performance and caused surface cracking, structural loosening, and granule disintegration. EPS analysis showed that PET-MNPs decreased EPS content, altered protein secondary structure, and increased hydrophilic functional groups, thereby weakening sludge bioadhesion. Metagenomic and metatranscriptomic analyses indicated that PET-MNPs inhibited the abundance and expression of genes involved in the Anammox process, tricarboxylic acid cycle, glycolysis/gluconeogenesis, and Wood-Ljungdahl pathway, resulting in insufficient ATP, NADH, and metabolic precursors required for EPS synthesis. Meanwhile, methionine and fatty acid metabolism were suppressed, limiting precursor supply for acyl-homoserine lactone (AHL) synthesis. Molecular docking showed that PET oligomers could stably bind to LuxR and potentially hinder AHL-LuxR complex formation. Exogenous AHL supplementation promoted EPS re-secretion, confirming the important role of QS imbalance in PET-MNPs-induced EPS reduction. Overall, PET-MNPs destabilized Anammox granular sludge through the combined effects of particle-induced physical damage and oligomer-mediated molecular interference. This study elucidates the molecular mechanism of MNP-induced Anammox granule disintegration and provides a theoretical basis for assessing the ecological risks of emerging pollutants in biological wastewater treatment.
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