The SPI-2 type III secretion system restricts motility of Salmonella- containing vacuoles

Abstract

Intracellular replication of Salmonella enterica occurs in membrane-bound compartments, called Salmonella -containing vacuoles (SCVs). Following invasion of epithelial cells, most SCVs migrate to a perinuclear region and replicate in close association with the Golgi network. The association of SCVs with the Golgi is dependent on the Salmonella- pathogenicity island-2 (SPI-2) type III secretion system (T3SS) effectors SseG, SseF and SifA. However, little is known about the dynamics of SCV movement. Here, we show that in epithelial cells, 2h were required for migration of the majority of SCVs to within 5μm from the microtubule organizing centre (MTOC), which is located in the same subcellular region as the Golgi network. This initial SCV migration was saltatory, bidirectional and microtubule-dependent. An intact Golgi, SseG and SPI-2 T3SS were dispensable for SCV migration to the MTOC, but were essential for maintenance of SCVs in that region. Live-cell imaging between 4 and 8h post invasion revealed that the majority of wild-type SCVs displaced less than 2μm in 20min from their initial starting positions. In contrast, between 6 and 8h post invasion the majority of vacuoles containing sseG, sseF or ssaV mutant bacteria displaced more than 2μm in 20min from their initial starting positions, with some undergoing large and dramatic movements. Further analysis of the movement of SCVs revealed that large displacements were a result of increased SCV speed rather than a change in their directionality, and that SseG influences SCV motility by restricting vacuole speed within the MTOC/Golgi region. SseG might function by tethering SCVs to Golgi-associated molecules, or by controlling microtubule motors, for example by inhibiting kinesin recruitment or promoting dynein recruitment. © 2007 The Authors; Journal compilation © 2007 Blackwell Publishing Ltd.