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

Kendal G Cooper,Victoria R Posada,Audrey Chong,Brendan Jeffrey,Canaan Whitfield-Cargile,Mary Krath,Craig Martens,Laszlo Kari,L Garry Adams,Molly Mcclurg,Sara D Lawhon,Sara V Little,Laura K Bryan,Richard C Laughlin,Olivia Steele-Mortimer,Tregei Starr

doi:10.1038/s41467-020-20558-6

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.

Highlights

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
By investigating the HilD regulon and focusing on both the ability to invade epithelial cells and motility, we identify the methyl-accepting chemotaxis protein (MCP), McpC, as a HilD-regulated protein that induces smooth swimming in T3SS1-expressing bacteria enhancing their net movement toward the mucosal epithelium
Since HilD is required for T3SS1 expression, mutants were internalized into human monocyte-derived macrophages (HuMDM) at a much lower level than WT (Fig. 1a)

Summary

Introduction

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). SPI1 encodes a type III secretion system (T3SS1), required for invasion of intestinal epithelial cells and gut inflammation, as well as several transcriptional regulators[8]. By investigating the HilD regulon and focusing on both the ability to invade epithelial cells and motility, we identify the methyl-accepting chemotaxis protein (MCP), McpC, as a HilD-regulated protein that induces smooth swimming in T3SS1-expressing bacteria enhancing their net movement toward the mucosal epithelium.

Methods

Results

Conclusion