Responses of wastewater biofilms to chronic CeO nanoparticles exposure: Structural, physicochemical and microbial properties and potential mechanism.

With the accelerated application of CeO nanoparticles (NPs), wastewater treatment plants will increasingly receive CeO NPs, thus inevitably causing CeO NPs to encounter microaggregates. Here, we comprehensively elucidate the responses in the structural, physicochemical and microbial properties of wastewater biofilms to chronic exposure (75 days) to different CeO NPs concentrations, with a particular emphasis on the protective mechanisms of stratified extracellular polymeric substances (EPSs). Chronic exposure to 0.1 mg/L CeO NPs boosted the content and broadened the distribution of α-d-glucopyranose polysaccharides (PS), while the sharply increased production and breadth of β-d-glucopyranose PS, forming a formidable shield, was a response to 10 mg/L CeO NPs. After the bacteria were exposed to CeO NPs, loosely bound EPSs (LB-EPSs) aggregated into macromolecules (increasing in apparent molecular weight (AMW)) but at a lower abundance, whereas the average AMW in tightly bound EPSs (TB-EPSs) decreased. The acetyl content and (α-helix+3-turn helix)/β-sheet value of TB-EPSs increased to resist CeO NPs. Furthermore, long-term exposure to CeO NPs decreased cell viability, reduced microbial diversity and shifted the microbial composition. N-acylated-l-homoserine lactone concentrations increased with increased density of Pseudomonas, which was associated with PS-regulated control, thus promoting PS production in EPSs in response to CeO NPs. These results expand the understanding of how microaggregates resist environmental stress caused by NPs.