Biochemical mechanism of p -cresol removal by Thauera aminoaromatica 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 p -cresol metabolism by the environmental denitrifier Thauera aminoaromatica S2, a pathway originally evolved for aromatic pollutant degradation. Proteomic stable isotope probing with 13 C-labeled p -cresol reveals strong incorporation of labeled carbon into T. aminoaromatica proteins, whereas parallel incubations with human fecal microbiomes show minimal incorporation, indicating limited intrinsic gut capacity for p -cresol utilization. Label-enriched proteins enable reconstruction of the anaerobic p -cresol degradation pathway and identification of key enzymes synthesized during growth on p -cresol. Moreover, hydrogel-encapsulated T. aminoaromatica remains active during co-incubation with the gut microbiome, achieving complete removal of 0.3 mM p -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 p -cresol removal.