The horizontally-acquired response regulator SsrB drives a Salmonella lifestyle switch by relieving biofilm silencing
Stuti K Desai,
Ricksen S Winardhi,
Saravanan Periasamy,
Michal M Dykas,
Yan Jie,
Linda J Kenney
Affiliations
Stuti K Desai
Mechanobiology Institute, National University of Singapore, Singapore, Singapore
Ricksen S Winardhi
Mechanobiology Institute, National University of Singapore, Singapore, Singapore; Department of Physics, National University of Singapore, Singapore, Singapore
Saravanan Periasamy
Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore, Singapore
Nanoscience and Nanotechnology Institute, National University of Singapore, Singapore, Singapore; Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore
Yan Jie
Mechanobiology Institute, National University of Singapore, Singapore, Singapore; Department of Physics, National University of Singapore, Singapore, Singapore
Linda J Kenney
Mechanobiology Institute, National University of Singapore, Singapore, Singapore; Jesse Brown Veterans Affairs Medical Center, University of Illinois-Chicago, Chicago, United States; Department of Microbiology and Immunology, University of Illinois-Chicago, Chicago, United States
A common strategy by which bacterial pathogens reside in humans is by shifting from a virulent lifestyle, (systemic infection), to a dormant carrier state. Two major serovars of Salmonella enterica, Typhi and Typhimurium, have evolved a two-component regulatory system to exist inside Salmonella-containing vacuoles in the macrophage, as well as to persist as asymptomatic biofilms in the gallbladder. Here we present evidence that SsrB, a transcriptional regulator encoded on the SPI-2 pathogenicity-island, determines the switch between these two lifestyles by controlling ancestral and horizontally-acquired genes. In the acidic macrophage vacuole, the kinase SsrA phosphorylates SsrB, and SsrB~P relieves silencing of virulence genes and activates their transcription. In the absence of SsrA, unphosphorylated SsrB directs transcription of factors required for biofilm formation specifically by activating csgD (agfD), the master biofilm regulator by disrupting the silenced, H-NS-bound promoter. Anti-silencing mechanisms thus control the switch between opposing lifestyles.
