Identification of Crp as a novel regulator of the Std fimbrial expression in .

The serovar Typhi genome contains 14 putative fimbrial systems. The Std fimbriae belong to the chaperone-usher family and its regulation has not been investigated in . Typhi. Several regulators of Std were previously identified in the closely related serovar Typhimurium. We hypothesize that regulators of . Typhimurium may be shared with . Typhi, but that several other regulators remain to be discovered. Here, we describe the role of more than 50 different candidate regulators on expression. Three types of regulators were investigated: known regulators in . Typhimurium, predicted regulators and virulence/metabolic regulators. Expression of was determined in the regulator mutants and compared with the wild-type strain. Overall, 21 regulator mutations affect promoter expression. The role of Crp, a newly identified factor for expression, was further investigated. Crp acted as an activator of expression on a distal region of the promoter region. Together, our results demonstrate the major influence of Crp as a novel transcriptional factor on promoter expression and later production of Std fimbriae in .