Microbial biodegradation of PFOS and PFPrA by Delftia acidovorans: Insights into microbial degradation pathways

The extreme chemical stability of per- and polyfluoroalkyl substances (PFAS) has led to their widespread and persistent accumulation in the environment, where they resist biological degradation. Microbial degradation offers a promising route for breaking down these recalcitrant pollutants; however, removal mechanisms have rarely been comprehensively analysed. This study investigates the biodegradability and biodegradation pathways of perfluorooctane sulfonate (PFOS) and perfluoropropanoic acid (PFPrA), while distinguishing microbial adsorption from biodegradation. Microbial species were isolated from a firefighting training site (Joroinen, Finland) contaminated with PFAS. Short-term (4-day) biodegradation studies showed that Delftia acidovorans was the most promising microbial species. Long-term (60-day) aerobic experiments showed that PFOS (initially 100 μg/L) was removed by biodegradation (49%) and adsorption (4%), with defluorination confirmed by fluoride release. PFPrA was removed solely by biodegradation (28%, initial concentration 100 μg/L). The most abundant transformation products (TP) from PFOS had a molecular weight of 136.05 Da, probably formed via hydrolase enzymes for C C cleavage and hydrolytic defluorination. Proteomic analysis revealed differential protein expression consistent with these proposed pathways, highlighting upregulated enzymes linked to hydrolytic defluorination and PFAS transformation. Only one TP (128.05 Da) was detected for PFPrA. These findings highlight the potential of D. acidovorans for PFAS biodegradation and provide insight into the microbial mechanism for breaking down these persistent pollutants.