Biochemical mechanism of <i>p</i> -cresol removal by <i>Thauera aminoaromatica</i> S2

Protein-bound uremic toxins are inefficiently cleared by dialysis and contribute to complications in chronic kidney disease, motivating approaches that target their gut-derived precursors. Here we investigate anaerobic <i>p</i> -cresol metabolism by the environmental denitrifier <i>Thauera aminoaromatica</i> S2, a pathway originally evolved for aromatic pollutant degradation. Proteomic stable isotope probing with ¹³ C-labeled <i>p</i> -cresol reveals strong incorporation of labeled carbon into <i>T. aminoaromatica</i> proteins, whereas parallel incubations with human fecal microbiomes show minimal incorporation, indicating limited intrinsic gut capacity for <i>p</i> -cresol utilization. Label-enriched proteins enable reconstruction of the anaerobic <i>p</i> -cresol degradation pathway and identification of key enzymes synthesized during growth on <i>p</i> -cresol. Moreover, hydrogel-encapsulated <i>T. aminoaromatica</i> remains active during co-incubation with the gut microbiome, achieving complete removal of 0.3 mM <i>p</i> -cresol in less than 10 hours, a timescale compatible with typical intestinal transit in the colon. Together, these findings establish a biochemical basis for repurposing environmental aromatic degradation pathways for gut-localized <i>p</i> -cresol removal.