Metabolic regulation driven by S-adenosylmethionine dictates specialized EPS assembly for enhanced arsenite...

Microbial extracellular polymeric substances (EPS) defend against arsenite (As(III)) stress, yet the metabolic drivers remain unclear. Using Clostridium acidisoli CK74X, a highly efficient arsenic-methylating strain from a mining area with strong resistance to arsenic, we investigated how As(III) exposure reshaped metabolism to influence EPS function. Sorption experiments and spectroscopic analyses revealed complementary roles of loosely‑bound and tightly‑bound EPS layers in As(III) sorption and transfer. At low As(III) concentrations (0.1, 1 μM), upregulation of type II polyketide biosynthesis and one-carbon metabolism promoted incorporation of aromatic and methyl groups into the EPS, enhancing As(III) bonding. High As(III) stress (10 μM) disrupted porphyrin and amino acid metabolism, suppressing EPS formation and function. Genomic analysis identified the arsM gene and a two‑step SAH recycling pathway (mtnN + luxS) that generates the AI‑2 quorum‑sensing molecule. Multiple perturbed pathways converged on S-adenosylmethionine (SAM) metabolism, which emerges as a central metabolic hub, executing a dual defense strategy: intracellular methylation and EPS modification. Based on these findings, we propose a conceptual model in which SAM‑driven EPS modulation serves as a targetable node for designing EPS‑based biosorbents, though further research on purification, regeneration, and field validation is needed. Overall, this study establishes a mechanistic link between metabolic regulation and EPS functional adaptation, advancing both fundamental understanding and bioremediation technologies.