Enterohemorrhagic <i>Escherichia coli</i> O157:H7 responds to norepinephrine gradients by tRNA reprogramming and codon-biased translation of virulence genes

Enterohemorrhagic <i>Escherichia coli</i> O157:H7 (EHEC) is a low-infectious-dose foodborne pathogen that uses norepinephrine gradients in the gut to locate sites for colonization and activate expression of virulence factors. Here, we identified features of transfer RNA (tRNA) reprogramming and codon-biased translation that play a role in this infectious process. Multivariate statistical analysis of genome-wide codon usage patterns revealed five gene clusters with unique codon biases, with one cluster containing all Locus of Enterocyte Effacement virulence genes that are all strongly biased for A/U-ending codons. EHEC cultures were then exposed to a norepinephrine gradient to induce type III secretion, as well as chemotaxis and flagellar motility, followed by a multi-omic interrogation of changes in tRNA modifications, tRNA abundance, and the proteome. We observed altered levels of multiple tRNA wobble modifications involved in G/C- versus A/U-ending codon recognition and a corresponding shift in the proteome toward genes enriched in A/U-ending codons. Our studies suggest EHEC can alter its tRNA pool in response to cues from the host, fine-tuning translational efficiency of its virulence program.IMPORTANCERegulation of microbial physiology and virulence during environmental changes has typically been ascribed to transcriptional mechanisms. Using convergent multi-omic technologies, we have discovered mechanisms of translational regulation of gene expression that regulate cell phenotype. Here, we applied these technologies to define mechanisms of translational regulation in the <i>Escherichia coli</i> O157:H7 response to norepinephrine exposure known to induce virulence.