Stimulating Acidimicrobium sp. Strain A6 in iron-rich, acidic sediments from AFFF-impacted sites for PFAS defluorination

Per- and polyfluoroalkyl substances (PFAS) are persistent and bioaccumulative contaminants that are widely used in industrial applications and consumer products and pose significant risks to ecosystems and human health. Acidimicrobium sp. Strain A6 (A6), which is common in acidic, and iron rich soils and sediments is capable of both anaerobic ammonium (NH₄⁺) oxidation under iron reduction (Feammox) and defluorination of perfluorinated alkyl substances, such as perfluoroalkyl acids (PFAAs). This study investigates the potential for biostimulating A6 via the supply of NH₄⁺ and ferric iron (Fe(III)) with the goal of defluorinating PFAAs. Sediment samples from acidic, iron-rich, AFFF (aqueous film forming foam) impacted sites were collected and incubated with added Fe(III) and NH₄⁺. Quantitative PCR was used to track A6 numbers as well as dehalogenase and F^- ion transporter genes during these incubations; changes in the microbial community structure were tracked through 16S rRNA gene sequencing. The findings reveal that the addition of Fe(III) and NH₄⁺ stimulated the Feammox reaction and A6 growth and enhanced the degradation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). Results also show a significant presence and activity of the above-mentioned genes in these incubations. The insights gained from this study could inform bioremediation strategies for PFAS-contaminated environments, especially in geochemical settings that favor the presence of A6.