The small nucleoid-binding proteins H-NS, HU, and Fis affect hilA expression in Salmonella enterica serovar Typhimurium

Abstract

hilA encodes an activator of Salmonella enterica serovar Typhimurium virulence genes and is transcriptionally modulated by environmental conditions. We show that H-NS represses hilA under low-osmolarity conditions. H-NS, HU, and Fis also appear to affect the derepression of hilA by HilD. Modulation of hilA by counteracting repressing and derepressing mechanisms may allow Salmonella serovar Typhimurium to regulate its virulence genes in response to different situations in vivo.

FIG. 1.

Effects of small nucleoid-binding proteins on hilA-lacZ expression. Salmonella serovar Typhimurium LT2 and SL1344 strains containing the hilA080::Tn5lacZY chromosomal fusion were grown under inducing (IND; white bars), repressing low-osmolarity (OSM; gray bars), or repressing aerobic (O2; black bars) conditions. β-Galactosidase activities are reported in Miller units and are the averages (± standard deviations) of values obtained from the results of at least two independent cultures during one representative experiment. Similar results were obtained in repeated experiments. (A) Fusion strain (wild type [WT]) and its hns-1::kan (hns) derivative; (B) hilC1::cam hilD1::kan (hilCD) and hilC1::cam hilD1::kan hns-1::kan (hilCD hns) derivatives; (C) fusion strain (WT) and its hupA::kan (hupA), hupB::kan (hupB), and hupA::kan hupB::kan (hupAB) derivatives; (D) hilC1::cam hilD1::kan (hilCD) and hilC1::cam hilD1::kan hupA::kan hupB::kan (hilCD hupAB) derivatives; (E) fusion strain (WT) and its fis3::cam (fis) derivative; (F) hilD1::kan (hilD) and hilD1::kan fis3::cam (hilD fis) derivatives.

FIG. 2.

Effect of small nucleoid-binding proteins on hilD mRNA levels. (A) The hilD transcription start site was determined by running primer extension products (hilD) from wild-type Salmonella serovar Typhimurium strain SL1344 RNA alongside dideoxy DNA sequencing reactions (GACT). Nucleotides marked with an asterisk represent two possible hilD transcription start sites on the template strand. (B) The positions of potential −10 and −35 σ⁷⁰ binding sites, the hilD translation start site (ATG), and the primer used in the primer extension reactions (LS49) are shown below the autoradiograph of the gel in relation to the hilD transcription start sites (+1). (C) hilD and ompA primer extension products were generated by using total RNA from wild-type (WT), hupA::kan hupB::kan (hup), fis3::cam (fis), and hns-1::kan (hns) derivatives of SL1344 or LT2, grown under inducing or low-osmolarity conditions, respectively. The autoradiographs shown are from one representative experiment.