RpoS activatesSalmonellaTyphi biofilms and drives persistence in a Zebrafish model

Abstract

AbstractThe development of strategies for targeting the asymptomatic carriage ofSalmonellaTyphi in chronic typhoid patients has suffered owing to our basic lack of understanding of the molecular mechanisms that enable the formation ofS.Typhi biofilms. Traditionally, studies have relied on cholesterol-attached biofilms formed by a closely related serovar, Typhimurium, to mimic multicellular Typhi communities formed on human gallstones. In long-term infections,S.Typhi adopts the biofilm lifestyle to persist in vivo and survive in the carrier state, ultimately leading to the spread of infections via the fecal-oral route of transmission. In the present work, we studiedS.Typhi biofilms directly, applied targeted as well as genome-wide genetic approaches to uncover unique biofilm components that do not conform to the CsgD-dependent pathway as established inS.Typhimurium. We adopted a genome-wideTn5mutation screen inS.Typhi in gallstone-mimicking conditions and generated New Generation Sequencing libraries based on the ClickSeq technology to identify the key regulators, IraP and RpoS, and the matrix components as Sth fimbriae, Vi capsule and lipopolysaccharide. We discovered that the starvation sigma factor, RpoS, was required for the transcriptional activation of matrix-encoding genes in vitro, and forS.Typhi colonization in persistent infections in vivo, using a heterologous fish larval model. Overall, our work established a novel RpoS-driven paradigm for the formation of cholesterol-attached Typhi biofilms and emphasized the role(s) of stress signaling pathways for adaptation in chronic infections.