Biophysical Society Thematic Meeting | Singapore

Mechanobiology of Disease

Thursday Speaker Abstracts

SsrB as a Driver of Lifestyle Changes in Salmonellae Stuti K. Desai 1 , Linda J. Kenney 1,2,3 , 1 Mechanobiology Institute, National University of Singapore, Singapore, 2 University of Illinois- Chicago, Chicago, IL, USA, 3 Jesse Brown VAMC, Chicago, IL, USA. SsrA/B is a two-component signaling system in Salmonella enterica that is encoded on one of the horizontally acquired AT-rich segments of the genome called Salmonella Pathogenecity Island-2 (SPI-2). It is essential for the successful existence of serovars Typhi and Typhimurium inside host cells and is absent in the nearest phylogenetic neighbor, S. bongori. In response to environmental stimuli such as changes in pH and osmolality, transcriptional activation of SPI-2 by SsrB~P regulates the intracellular lifestyle of Salmonella. However, for successful pathogenesis in terms of carriage and persistence, Salmonella exists as multicellular communities. We recently found that this sessile lifestyle was also regulated by SsrB. SsrB activated the expression of the master regulator of biofilm formation, csgD (agfD), in the absence of any phosphate donors, including SsrA. This was achieved by relieving transcriptional silencing by H-NS at the csgD regulatory region. Atomic force microscopy revealed that the full- length unphosphorylated SsrB was bound to the upstream regulatory region of csgD, in agreement with our genetic and biochemical results. This binding and subsequent changes in the local DNA topology was sufficient to partially drive off H-NS and activate csgD expression. In contrast, SsrB~P regulates expression of the SPI-2 regulon by both direct transcriptional activation and anti-silencing. Our findings unravelled a novel role for unphosphorylated SsrB in regulating gene expression and established the mechanism by which anti-silencing occured. Therefore, depending on its phosphorylation state, SsrB, assists Salmonella Typhimurium to decide its lifestyle choice: intracellular versus the carrier state or biofilms. Building on this paradigm, we are now studying the larger role of SsrB and SsrB~P in regulating enivronmentally sensitive genes as Salmonella alternates between the two lifestyles. Deciphering the SsrB versus SsrB~P regulons in Typhimurium will also help to understand the carrier state of Typhi.

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