Catabolism of serine enantiomers represses enterohemorrhagic Escherichia coli virulence factors via modulation of the nitrogen stress response
- Emily Addington
- Kabo R. Wale
- Emily Horsburgh
- Margot Fargeas
- Leonidas Spathis
- Weronika Leśniak
- Saoirse Flavin
- Patricia T. Rimbi
- David R. Mark
- Sofia Sandalli
- Ester Serrano
- Gavin Blackburn
- Clement Regnault
- Phillip D. Whitfield
- James P. R. Connolly
- Andrew J. Roe
- Nicky O’Boyle
2026-03-18
Attaching and effacing pathogens, including enterohemorrhagic Escherichia coli (EHEC), colonize their preferred intestinal niche by sensing diverse host-, diet-, and microbiota-derived signals and coordinating the expression of virulence factors. D-serine, a host metabolite abundant in urine but scarce in the intestine, restricts EHEC colonization by transcriptionally repressing the type 3 secretion system (T3SS) while activating the SOS stress response. However, the mechanism underlying virulence regulation by D-serine remains unestablished. Here, we show that multiple amino acids, including L-serine converge on this pathway, repressing the T3SS without inducing the SOS response. Transcriptomic analyses showed a common response to D- and L-serine dominated by repression of nitrogen stress response genes. Mutational analysis identified the response regulators NtrC and Nac as essential mediators of T3SS repression by both serine enantiomers. Disruption of L-serine deaminase enzymes crucially revealed that T3SS repression depends on cytoplasmic ammonia/ammonium release rather than sensing of intact serine. While EHEC lacks canonical D-serine catabolic capacity, through metabolomics we provide evidence of oxidative deamination activity, capable of producing this regulatory signal. Together, these findings establish a mechanistic link between amino acid catabolism, nitrogen stress signaling, and virulence regulation in EHEC, highlighting how metabolic flux fine-tunes pathogen adaptation to intestinal niches.