Toxicity of perfluorinated compounds to iron-reducing bacteria and their inhibitory effects on extracellular electron transfer

Microbial iron reduction regulates biogeochemical cycles in anoxic environments, yet it is increasingly threatened by the widespread presence of environmental pollutants. Among these, the impact of per- and polyfluoroalkyl substances (PFAS) on iron-reducing bacteria is often overlooked. This study investigated the toxicological mechanisms of three PFAS: long-chain perfluorooctanoic acid, short-chain perfluorobutanoic acid, and hexafluoropropylene oxide dimer acid, on Shewanella oneidensis MR-1, while delineating how their distinct chain lengths/structures disrupt extracellular electron transfer pathways. At 20 mg/L, all PFAS exhibited concentration-dependent inhibition of bacterial growth and significantly suppressed dissimilatory iron reduction (DIR) efficiency. Cellular analyses revealed all three PFAS undermined cell structural integrity, increased membrane permeability, and triggered oxidative damage. Critically, PFAS exposure impairs the biosynthesis of electron transport chain components, including c-type cytochromes and riboflavin, thereby reducing electron flux efficiency and disrupting DIR performance. Transcriptomic profiling corroborated that PFAS-induced downregulation of electron transport chain-related genes and revealed multi-level toxicity mechanisms, including inhibited ribosome biogenesis, impaired energy metabolism, and dysregulated amino acid conversion. Furthermore, PFAS mixtures exhibited synergistic toxicity to iron-reducing bacteria, highlighting potential ecological risks at environmentally relevant concentrations. These findings advance our understanding of PFAS ecotoxicity and highlight their potential to impair microbial processes critical to elemental cycling in anoxic ecosystems.