One of the main concerns in industrialized countries is represented by per- and poly-fluoroalkyl substances (PFAS), persistent contaminants hardly to be dealt with by conventional wastewater treatment processes. Phyco-remediation was proposed as a green alternative method to treat wastewater. Synechocystis sp. PCC6803 is a unicellular photosynthetic organism candidate for bioremediation approaches based on synthetic biology, as it is able to survive in a wide range of polluted waters. In this work, we assessed the possibility of applying Synechocystis in PFAS-enriched waters, which was never reported in the previous literature. Respirometry was applied to evaluate short-term toxicity of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), which did not affect growth up to 0.5 and 4 mg L⁻¹, respectively. Continuous and batch systems were used to assess the long-term effects, and no toxicity was highlighted for both compounds at quite high concentration (1 mg L⁻¹). A partial removal was observed for PFOS and PFOA, (88% and 37%, with removal rates of about 0.15 and 0.36 mg L⁻¹ d⁻¹, respectively). Measurements in fractionated biomass suggested a role for Synechocystis in the sequestration of PFAS: PFOS is mainly internalized in the cell, while PFOA is somehow transformed by still unknown pathways. A preliminary bioinformatic search gave hints on transporters and enzymes possibly involved in such sequestration/transformation processes, opening the route to metabolic engineering in the perspective application of this cyanobacterium as a new phyco-remediation tool, based on synthetic biology.

PFASs are a group of pollutants ubiquitous in the environment, for which their effects on the microbial community composition and activity of anaerobic granular sludge are still poorly understood. With our study, we aimed to provide insight into the impact of four PFASs on the methane yield of anaerobic granular sludge (AGS) using acetate as the substrate. Anaerobic granular sludge was exposed to different concentrations of 1H,1H,2H,2H-Tridecafluorooctan-1-ol (6:2FTOH), 1H,1H,2H,2H-Perfluoro-1-decanol (8:2FTOH), Tridecafluorohexane-1-sulfonic acid (PFHxS) and Perfluorooctanoic acid (PFOA). While the two fluorotelomers caused marginal changes in methane production, PFHxS and PFOA greatly inhibited acetoclastic methanogenesis. Depending on the concentration, the AGS could recover its activity after a certain number of hours when incubated with PFASs. The 50% Inhibitory Concentration (IC ₅₀ ) of the methane production was estimated to be 278.98 (± 3.2) mg/L for PFOA and 1,091.9 (± 26.78) mg/L for PFHxS. PFASs exposure also influenced the archaeal and eubacterial communities. The most significant change was observed with the eubacterial community, which showed an increase in the relative abundance of the genus Sulfurospirillum in the samples treated with 2,000 mg/L of 8:2FTOH and 600 mg/L of PFOA, whose presence grew to represent 16.65% and 45.4% of all reads in those samples. These findings provide insight into the differential impact of PFASs on methanogenic processes and highlight their potential to disrupt key microbial functions in anaerobic systems.