Microbial Responses to PFOA in Coastal Wetland: An Ecological Comparison Between Freshwater and Salt Marsh

Coastal wetlands provide critical ecosystem services yet face increasing per- and polyfluoroalkyl substance (PFAS) contamination, and comparison of wetland microbiome responses to PFAS remains poorly resolved. Laboratory-enriched microbial consortia derived from freshwater marsh and salt marsh soils were exposed to perfluorooctanoic acid (PFOA) in 75-day microcosms at 0, 1, and 10 mg/L, then characterized by 16S rRNA gene sequencing, phylogenetic null modeling, neutral community modeling, and KEGG-level functional prediction. Both enriched consortia showed a modest decrease in aqueous PFOA (~11–13%) at 1 mg/L but not at 10 mg/L, consistent with a potential contribution from biosorption-mediated immobilization. Incubation time dominated beta-diversity shifts (ANOSIM R > 0.90, p = 0.001), while PFOA produced no detectable compositional separation. Exploratory additive mixed-effects models indicated that alpha diversity varied primarily with microbial community source and sampling day, whereas PFOA concentration showed a nominal overall association only with Shannon diversity. Assembly analyses showed that PFOA was associated with stronger heterogeneous selection in the salt-marsh-derived consortium, whereas the freshwater-derived consortium remained stochastically dominated. When PFOA-exposed samples were pooled across both enriched consortia, the neutral community model fit collapsed (R2 < 0), signaling a regime shift toward deterministic, PFOA-mediated selection. Functionally, the salt-marsh-derived consortium showed predicted enrichment in taurine/hypotaurine metabolism and broad-spectrum proteolytic functions (serralysin and creatinase), whereas the freshwater-marsh-derived consortium showed predicted enrichment in glutathione metabolism, xenobiotic dioxygenase functions, and DNA repair pathways. Candidate PFOA-sensitive (Pseudohongiella, Flavobacterium, Parvibaculum) and PFOA-tolerant (Sericytochromatia, Legionella) taxa were identified as source-associated candidate biomarkers. Under the tested culture conditions, PFOA responses differed between the laboratory-enriched freshwater-marsh- and salt-marsh-derived bacterial consortia. These results describe source-associated responses of the enriched consortia but may need further validation with native wetland communities.