MglA regulates Francisella tularensis subsp. novicida (Francisella novicida) response to starvation and oxidative stress

Abstract

MglA is a transcriptional regulator of genes that contribute to the virulence of Francisella tularensis, a highly infectious pathogen and the causative agent of tularemia. This study used a label-free shotgun proteomics method to determine the F. tularensis subsp. novicida (F. novicida) proteins that are regulated by MglA. The differences in relative protein amounts between wild-type F. novicida and the mglA mutant were derived directly from the average peptide precursor ion intensity values measured with the mass spectrometer by using a suite of mathematical algorithms. Among the proteins whose relative amounts changed in an F. novicida mglA mutant were homologs of oxidative and general stress response proteins. The F. novicida mglA mutant exhibited decreased survival during stationary-phase growth and increased susceptibility to killing by superoxide generated by the redox-cycling agent paraquat. The F. novicida mglA mutant also showed increased survival upon exposure to hydrogen peroxide, likely due to increased amounts of the catalase KatG. Our results suggested that MglA coordinates the stress response of F. tularensis and is likely essential for bacterial survival in harsh environments.

FIG. 1.

F. novicida mglA exhibits decreased survival during stationary-phase growth in growth-restrictive MHB medium. Growth rates of wild-type F. novicida (•) and the mglA mutant (▴) in MHB at 37°C are shown. Lysis of F. novicida mglA cultures was observed after 24 h of growth. Error bars represent standard deviation (n = 3).

FIG. 2.

Susceptibilities of the wild-type F. novicida (black bars), mglA mutant (white bars), and katG mutant (gray bars) strains to paraquat (A) and H₂O₂ (B) were measured by the disk-diffusion assay. Error bars represent standard deviation (n = 3). A P value of <0.01 for differences between the strains was determined by t test.