Perfluorooctanoic Acid Can Increase Biofilm Resilience and Virulence in Drinking Water Distribution Systems

Despite the prevalence of perfluorooctanoic acid (PFOA) in drinking water distribution systems (DWDSs), its effects on biofilm formation and tolerance to residual disinfectants remain largely unknown. Here, we report that DWDS-relevant levels of PFOA (1-80 ng/L) promoted <i>Pseudomonas aeruginosa</i> biofilm formation (by 1.8- to 4.5-fold) and chlorine tolerance (by 7-22%). PFOA also enhanced biofilm tolerance to common antibiotics, increasing their minimum inhibitory concentrations by 25-67%. In a flow-through system, biofilm evolution toward higher resilience was attributed to PFOA-exerted oxidative stress, which fortuitously upregulated quorum sensing and stimulated extracellular polymeric substances production. PFOA exposure also increased bacterial chemotaxis and activated <i>cyaA</i> and <i>cyaB</i> genes, which enhanced the cAMP/Vfr signaling pathway, contributing to the upregulation of virulence factor genes. PFOA-induced chlorine and antibiotic resistance and increased virulence were also verified with a mesocosm system and a real DWDS pipeline biofilm. Overall, these results underscore the need for proactive microbial risk assessment associated with such indirect effects of emerging pollutants in DWDSs.