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The ins and outs of virulence gene expression: Mg2+ as a regulatory signal
1Howard Hughes Medical Institute, Washington University School of Medicine, Department of Molecular Microbiology, St. Louis, MO 63110, USA. groisman@borcim.wustl.edu
Abstract:
The facultative intracellular pathogen Salmonella enterica serovar Typhimurium faces multiple environments during infection, including different cell types as well as extracellular fluids. We propose that Salmonella ascertains its cellular location by assessing the Mg2+ concentration of its milieu. A signal transduction system, PhoP/PhoQ, signals Salmonella its presence in a intracellular (low Mg2+) or extracellular (high Mg2+) environment, thereby promoting transcription of genes required for survival within or entry into host cells. The PhoP/PhoQ system is high in a regulatory hierarchy that controls other signal transduction systems that respond to different host cues, enabling the microorganism to determine its precise tissue and cellular location.
Insights
Salmonella Typhimurium senses its location by detecting magnesium (Mg2+) levels. The PhoP/PhoQ system helps it survive inside or enter host cells.
Area of Science:
- Microbiology
- Pathogen Biology
- Signal Transduction
Background:
- Salmonella enterica serovar Typhimurium is a facultative intracellular pathogen.
- It encounters diverse environments during infection, including intracellular and extracellular spaces.
- Pathogens must adapt to different host niches for survival and virulence.
Purpose of the Study:
- To investigate how Salmonella Typhimurium senses its location within a host.
- To elucidate the role of the PhoP/PhoQ signal transduction system in environmental sensing.
- To understand how environmental cues regulate bacterial gene expression for host cell interaction.
Main Methods:
- The study focuses on the PhoP/PhoQ signal transduction system.
- It proposes magnesium (Mg2+) concentration as a key environmental cue.
- Gene transcription changes in response to Mg2+ levels were investigated.
Main Results:
- The PhoP/PhoQ system detects extracellular (high Mg2+) and intracellular (low Mg2+) environments.
- This sensing mechanism regulates the transcription of genes crucial for Salmonella survival.
- Genes involved in host cell entry and intracellular survival are differentially expressed.
- PhoP/PhoQ acts as a master regulator for other signal transduction pathways.
Conclusions:
- Salmonella Typhimurium utilizes Mg2+ concentration as a primary signal to determine its location.
- The PhoP/PhoQ system is central to Salmonella's adaptive response to host environments.
- This regulatory system enables Salmonella to optimize gene expression for survival and pathogenesis within host cells.