TusDCB-mediated tRNA sulfur modification is required for virulence and intestinal fitness in enterohemorrhagic Escherichia coli.

Sulfur modification of tRNAs enhances translational accuracy and efficiency, yet its contribution to bacterial pathogenesis remains poorly understood. In Escherichia coli, the TusDCB complex catalyzes 2-thiolation of wobble uridines in lysine-, glutamate-, and glutamine-decoding tRNAs. To investigate its role in intestinal virulence, we constructed an in-frame tusDCB deletion mutant in enterohemorrhagic Escherichia coli (EHEC). Comparative analyzes revealed that deletion of tusDCB reduced transcription of type III secretion system (T3SS) genes and secretion of the T3SS translocator EspB, resulting in diminished T3SS-dependent hemolytic activity. In a Citrobacter rodentium mouse infection model, the tusDCB mutant showed attenuated colonic inflammation and reduced lethality compared with the parent strain. The mutant also displayed increased sensitivity to acid and oxidative stress, but no change in bile salt tolerance. Proteomic analysis identified decreased abundance of multiple proteins, including the T3SS translocator EspB and tryptophanase (TnaA), accompanied by loss of indole production and increased susceptibility to fosfomycin. Complementation of tusDCB restored these phenotypes, confirming its contribution to virulence-associated functions. Together, these findings indicate that TusDCB-mediated tRNA sulfur modification supports optimal T3SS expression, stress resistance, and bacterial fitness, thereby promoting intestinal pathogenicity in EHEC.