Metatranscriptomic Insights into Microbial Responses of a Bacterial Consortium from Activated Sludge at the Zeekoegat Wastewater Treatment Plant to Perfluorooctane Sulfonate and Perfluorooctanoic Acid

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are persistent pollutants resistant to conventional treatment processes and pose significant environmental risks. The aim of this study was to comparatively evaluate the metatranscriptomic responses of activated sludge bacterial communities to PFOS and PFOA exposure at environmentally relevant (150 ng/L) and elevated (1050 ng/L) concentrations. Activated sludge from the Zeekoegat Wastewater Treatment Plant (Pretoria, South Africa) was used under aerobic conditions for 45 days. Taxonomic profiling revealed a Proteobacteria-dominated community with distinct pollutant-specific shifts. Under PFOA exposure, Pseudomonas dominated at low concentration, while Achromobacter and Burkholderia increased at higher levels. Under PFOS exposure, Kerstersia dominated at low concentration, whereas Comamonas, Sphingopyxis, and Polaromonas were enriched at higher concentration. Functional analysis revealed increased abundance of stress-response and metabolic pathways, including ABC transporters, chaperonins (GroEL), and β-oxidation. Overall, the results indicate a dose-dependent microbial adaptation, with pollutant type driving functional responses. These findings highlight pollutant-specific microbial responses and adaptation under PFAS exposure in activated sludge systems. These findings highlight pollutant-specific microbial strategies and the potential of activated sludge microbiomes in PFAS transformation processes.