Dual role of the MgtC virulence factor in host and non-host environments

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• The MgtC protein is crucial for intracellular pathogen replication within macrophages and bacterial growth in low magnesium environments.
• A link between these phenotypes is hypothesized due to magnesium depletion within the phagosome.
• MgtC proteins share a conserved N-terminal transmembrane domain and a variable C-terminal domain.

Purpose of the Study:

• To investigate the dual role of MgtC in bacterial intramacrophage survival and low magnesium growth.
• To determine if MgtC homologues from other bacteria can complement the functions of Salmonella MgtC.
• To identify specific amino acid changes affecting MgtC's distinct functions.

Main Methods:

• Computational prediction and experimental analysis of the Salmonella MgtC C-terminal domain structure and function.
• Expression of MgtC homologues from Yersinia pestis, Photorhabdus luminescens, and Pseudomonas aeruginosa in a Salmonella DeltamgtC strain.
• Site-directed mutagenesis to identify key amino acids involved in MgtC function.

Main Results:

• The Salmonella MgtC C-terminal domain is cytoplasmic, possesses a fold similar to metal transporters, and does not bind magnesium.
• Yersinia pestis MgtC fully complemented Salmonella DeltamgtC, while Photorhabdus luminescens and Pseudomonas aeruginosa MgtC only complemented in low magnesium conditions, dissociating the phenotypes.
• Specific amino acid substitutions altered MgtC's role in macrophages without affecting its low magnesium growth function.
• Salmonella DeltamgtC exhibited altered morphology (elongation, autoaggregation) in low magnesium but not in macrophages.

Conclusions:

• MgtC exhibits distinct roles in bacterial intramacrophage survival and adaptation to low magnesium environments.
• The study successfully dissociated the previously linked phenotypes of MgtC.
• Specific regions or residues of MgtC differentially regulate its function in different environments.