Repression of intracellular virulence factors in Salmonella by the Hha and YdgT nucleoid-associated proteins - PubMed (original) (raw)
Repression of intracellular virulence factors in Salmonella by the Hha and YdgT nucleoid-associated proteins
Umaporn Silphaduang et al. J Bacteriol. 2007 May.
Abstract
The Hha/YmoA family of nucleoid-associated proteins is involved in gene regulation in enterobacteria. In Salmonella enterica serovar Typhimurium, virulence genes required for intracellular growth are induced following host cell invasion but the proteins responsible for repressing these genes prior to host cell entry have not been fully identified. We demonstrate here that Hha is the major repressor responsible for silencing virulence genes carried in Salmonella pathogenicity island 2 prior to bacteria sensing an intracellular environmental cue.
Figures
FIG. 1.
Deletion of hha increases SseB protein levels. Bacterial cultures (wild type [wt] and Δ_ydgT_, Δ_hhaT_, and Δ_ydgT_ Δ_hha_ mutants) were grown under SPI-2-inducing conditions in LPM (pH 5.8) (A) and under SPI-2-repressing conditions in LB broth (B) as described in the text. Bacterial cell lysates were probed by Western blot analysis for the SPI-2-encoded protein, SseB (top panels), and a control protein (intracellular DnaK) (bottom panels). (C) Complementation of hha deletion. Wild-type Salmonella serovar Typhimurium and the Δ_hha_ mutant were transformed with p_hha_, carrying the full-length wild-type hha strain from an IPTG-inducible promoter. Strains were grown in LB and probed by Western blot analysis for SseB as described in the text. The data shown are representative of experiments performed three times.
FIG. 2.
Transcriptional activity of the SPI-2 effector operon promoter (P_sseA_) is derepressed upon deletion of hha and requires SsrB for activity. The β-galactosidase activity of a chromosomal P_sseA_::lacZ reporter was examined in the indicated strains during growth under (A) SPI-2-inducing conditions (LPM at pH 5.8) and (B) noninducing conditions (LB). The data are means and standard deviations (SD) from triplicate determinations from two independent experiments. (C) The β-galactosidase activity of a chromosomal P_sseA_::lacZ reporter was examined in wild-type Salmonella (wt), in mutants lacking the response regulator, ssrB, or the repressor, hha, and in a double mutant lacking both ssrB and hha. The data are the means and SD from triplicate determinations from two experiments. P was <0.001 for the Δ_hha_ strain compared to the wild type. RLU, relative light units; OD600, optical density at 600 nm.
FIG. 3.
Competitive infections in mice. Mice were infected with a mixed inoculum of wild-type Salmonella serovar Typhimurium (wt) and either an hha mutant (left) or an hha ydgT double mutant (right). The CI for the hha strain and ydgT hha strain were determined for the spleen and liver at 72 h postinfection. Each data point represents one animal, and horizontal bars indicate geometric means. CI for hha/wt, P = 0.021 (spleen) and P = 0.001 (liver); CI for ydgT hha/wt, P < 0.0001 for spleen and liver.
References
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