-Cresol Production Is Induced by the Precursor -Hydroxyphenylacetate.

is an etiological agent for antibiotic-associated diarrheal disease. produces a phenolic compound, -cresol, which selectively targets gammaproteobacteria in the gut, facilitating dysbiosis. decarboxylates -hydroxyphenylacetate (-HPA) to produce -cresol by the action of the HpdBCA decarboxylase encoded by the operon. Here, we investigate regulation of the operon and directly compare three independent reporter systems; SNAP-tag, glucuronidase , and alkaline phosphatase reporters to detect basal and inducible expression. We show that expression of is upregulated in response to elevated -HPA. analysis identified three putative promoters upstream of operon-P, P, and Pσ; only the P promoter was responsible for both basal and -HPA-inducible expression of We demonstrated that turnover of tyrosine, a precursor for -HPA, is insufficient to induce expression of the operon above basal levels because it is inefficiently converted to -HPA in minimal media. We show that induction of the operon in response to -HPA occurs in a dose-dependent manner. We also identified an inverted palindromic repeat (AAAAAG-N-CTTTTT) upstream of the start codon (ATG) that is essential for inducing transcription of the operon in response to -HPA, which drives the production of -cresol. This provides insights into the regulatory control of -cresol production, which affords a competitive advantage for over other intestinal bacteria, promoting dysbiosis. infection results from antibiotic-associated dysbiosis. -Cresol, a phenolic compound produced by , selectively targets gammaproteobacteria in the gut, facilitating dysbiosis. Here, we demonstrate that expression of the operon, encoding the HpdBCA decarboxylase which converts -HPA to -cresol, is upregulated in response to elevated exogenous -HPA, with induction occurring between >0.1 and ≤0.25 mg/ml. We determined a single promoter and an inverted palindromic repeat responsible for basal and -HPA-inducible expression. We identified turnover of tyrosine, a -HPA precursor, does not induce expression above basal level, indicating that exogenous -HPA was required for -cresol production. Identifying regulatory controls of -cresol production will provide novel therapeutic targets to prevent -cresol production, reducing 's competitive advantage.