Endoplasmic Reticulum contact sites facilitate the coordinated division of Salmonella-containing vacuole (SCV)

Salmonella Typhimurium (STM) resides in a membrane-bound compartment called Salmonella containing vacuole (SCV) in several infected cell types. Within host cells, the division of bacteria and SCV are synchronous to maintain the single bacterium per vacuole. However, the mechanism regulating the synchronous fission and the machinery is not well understood. The fission of several intracellular organelles is regulated by the dynamic nature of the tubular endoplasmic reticulum (ER). In this study, we have evaluated the role of ER in controlling SCV fission. Interestingly, Salmonella-infected cells show the activation of unfolded protein response (UPR) with expanded ER tubules compared to the uninfected cells. Further, changing the expression of ER morphology regulators, such as reticulon-4a (Rtn4a) and CLIMP63, affected bacterial proliferation significantly, suggesting a potential role for tubular ER in facilitating the SCV division. Live-cell imaging analysis shows the marking of tubular ER precisely at the center of the majority of SCV division (78%) sites. We have investigated the role of SteA (a known Salmonella effector in modulating the membrane dynamics) in coordinating the SCV division. We observed that SteA resides on the SCV membranes and helps in making membrane contact sites between SCV and ER. Accordingly, the colocalization of ER with SCV enclosing SteA mutant Salmonella was significantly reduced compared to SCV-formed by wild-type Salmonella. Depletion of steA in Salmonella resulted in profound defects in SCV division, resulting in multiple bacteria residing in a single vacuole with defects in proliferation compared to the wild-type strain in epithelial cells. Also, during in vivo infection, the STM{Delta}steA mutant shows a defect in colonization in the spleen and liver and affects the initial survival rate of mice. Overall, this study suggests a coordinated role of bacterial effector SteA in promoting the ER contact sites with SCVs and thus regulating the successful division of SCV. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=187 SRC="FIGDIR/small/592158v2_ufig1.gif" ALT="Figure 1000"> View larger version (72K): org.highwire.dtl.DTLVardef@21e83aorg.highwire.dtl.DTLVardef@157052org.highwire.dtl.DTLVardef@1815308org.highwire.dtl.DTLVardef@1724888_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG