Endoplasmic reticulum facilitates the coordinated division of <i>Salmonella</i> -containing vacuoles

<i>Salmonella</i> Typhimurium (STM) resides in a membrane-bound compartment called the <i>Salmonella</i>-containing vacuole (SCV) in several infected cell types where bacterial and SCV division occur synchronously to maintain a single bacterium per vacuole. However, the mechanism behind this synchronous fission is not well understood. Fission of intracellular organelles is known to be regulated by the dynamic tubular endoplasmic reticulum (ER). In this study, we evaluated the role of ER in controlling SCV division. Interestingly, <i>Salmonella</i>-infected cells show activation of the unfolded protein response (UPR) and expansion of ER tubules. Altering the expression of ER morphology regulators, such as reticulon-4a (Rtn4a) and CLIMP63, significantly impacted bacterial proliferation, suggesting a potential role of tubular ER in facilitating SCV division. Live-cell imaging revealed the marking of tubular ER at the center of 78% of SCV division sites. This study also explored the role of SteA (a known <i>Salmonella</i> effector in modulating membrane dynamics) in coordinating the SCV division. SteA resides on the SCV membranes and helps form membrane contact between SCV and ER. The colocalization of ER with SCV enclosing STMΔ<i>steA</i> was significantly reduced, compared with SCV of STM WT or STMΔ<i>steA:steA</i>. STMΔ<i>steA</i> shows profound defects in SCV division, resulting in multiple bacteria in a single vacuole with proliferation defects. <i>In vivo</i>, the STMΔ<i>steA</i> 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 ER contact/association with SCVs and regulating SCV division.IMPORTANCEThis study highlights the essential role of the host endoplasmic reticulum in facilitating SCV division and maintaining a single bacterium per vacuole. The <i>Salmonella</i> effector SteA helps maintain the single bacterium per vacuole state. In the absence of SteA, <i>Salmonella</i> resides as multiple bacteria within a single large vacuole. The STMΔ<i>steA</i> shows reduced proliferation under <i>in vitro</i> conditions and exhibits colonization defects <i>in vivo</i>, highlighting the importance of this effector in <i>Salmonella</i> pathogenesis. These findings suggest that targeting SteA could provide a novel therapeutic approach to inhibit <i>Salmonella</i> pathogenicity.