Regulatory protein HilD stimulates Salmonella Typhimurium invasiveness by promoting smooth swimming via the methyl-accepting chemotaxis protein McpC

Abstract

In the enteric pathogen Salmonella enterica serovar Typhimurium, invasion and motility are coordinated by the master regulator HilD, which induces expression of the type III secretion system 1 (T3SS1) and motility genes. Methyl-accepting chemotaxis proteins (MCPs) detect specific ligands and control the direction of the flagellar motor, promoting tumbling and changes in direction (if a repellent is detected) or smooth swimming (in the presence of an attractant). Here, we show that HilD induces smooth swimming by upregulating an uncharacterized MCP (McpC), and this is important for invasion of epithelial cells. Remarkably, in vitro assays show that McpC can suppress tumbling and increase smooth swimming in the absence of exogenous ligands. Expression of mcpC is repressed by the universal regulator H-NS, which can be displaced by HilD. Our results highlight the importance of smooth swimming for Salmonella Typhimurium invasiveness and indicate that McpC can act via a ligand-independent mechanism when incorporated into the chemotactic receptor array.

High-Definition DIC Imaging Uncovers Transient Stages of Pathogen Infection Cycles on the Surface of Human Adult Stem Cell-Derived Intestinal Epithelium

“…S2 A and C) but importantly did not allow simultaneous visualization of epithelial surface topology. These observations validate and extend previous studies of Salmonella motility ( 3 , 35 , 38 – 40 ) by mapping Salmonella NSS parameters atop a physiologically arranged epithelial surface and under minimally perturbing conditions.…”

“…S2C ) and mean turning angle of ∼14.68°/15 μm clockwise ( Fig. S2E ), corresponding to its flagellum’s counterclockwise spin ( 37 , 38 ). Reassessment of this pattern by fluorescence imaging resulted in broadly similar tracks ( Fig.…”

High definition DIC imaging uncovers transient stages of pathogen infection cycles on the surface of human adult stem cell-derived intestinal epithelium

“…Reassessment of this pattern by fluorescence imaging resulted in broadly similar tracks (Fig S2A ,C), but importantly did not allow simultaneous visualization of epithelial surface topology. These observations validate and extend previous studies of Salmonella motility (3,33,(36)(37)(38), by mapping Salmonella NSS parameters atop a physiologically arranged epithelial surface and under minimally perturbing conditions.…”

“…The resulting filtered image stack enabled both segmentation of motile bacteria and automated particle tracking without the use of fluorescent markers (Fig 2A - bottom row panels, movie will be provided upon publication). Automated tracking of Salmonella NSS in the TM 2 filtered stack showed a variety of curved tracks with a mean speed of 34.7 μm/s (Fig 2B, Fig S2C) and mean turning angle of ∼14.68°/15 μm clockwise (Fig S2E), corresponding to its flagella’s counterclockwise spin (35, 36). Reassessment of this pattern by fluorescence imaging resulted in broadly similar tracks (Fig S2A,C), but importantly did not allow simultaneous visualization of epithelial surface topology.…”

“…To leverage this possibility, we explored motility of two microbes atop IEC monolayers grown in AMCs: the smaller bacterial pathogen Salmonella, and the larger protozoan parasite Giardia. to its flagella's counterclockwise spin (35,36). Reassessment of this pattern by fluorescence imaging resulted in broadly similar tracks (Fig S2A ,C), but importantly did not allow simultaneous visualization of epithelial surface topology.…”