Genome-Wide Scan of the Gene Expression Kinetics of Salmonella enterica Serovar Typhi during Hyperosmotic Stress

Abstract

Salmonella enterica serovar Typhi is a human enteroinvasive pathogen that canovercome the stress caused by the high osmolarity of the human small intestine and causesystemic infection. To investigate the global transcriptional regulations of S. entericaserovar Typhi exposed to a hyperosmotic environment, a genomic oligo-DNA microarraycontaining 4474 Salmonella genes was prepared. A wild strain of S. enterica serovar TyphiGIFU10007 was grown in LB medium containing 50 mM NaCl to simulate a low osmoticenvironment. The hyperosmotic stress was simulated by an osmotic up-shift, whichincreased the concentration of NaCl in the LB from 50 mM to 300 mM. Genome-wide geneexpressions of S. enterica serovar Typhi at 15 min, 30 min, 60 min, and 120 min after theosmotic up-shift were investigated by the microarray analysis. Gene expression profiles insomewhat later stage (60 ~120 min) of the stress were quite different from those in the earlystage (0 ~ 30 min) of the stress. At 120 min after the osmotic stress, the expression levels of889 genes were obviously changed. However, expression levels of only 382 genes weresignificantly changed at 15 min after the osmotic stress. The expression levels of most SPI-1genes associated with invasion of the pathogen were increased at 120 min after the osmoticup-shift, but were not obviously changed at 15 min or 30 min after the osmotic stress.Expressions of a central regulatory gene, phoP, and sigma factor genes rpoE, rpoD, andrpoS were also changed with different profiles during the osmotic stress. These resultsindicated that the invasive ability of the pathogen is significantly increased after 2 h of hyperosmotic stress, and regulator PhoP and sigma factors RpoE, RpoD appear to participate in the network regulatory mechanisms that benefit the pathogen to adapt hyperosmotic environmental conditions. The later increased invasive ability of S. enterica serovar Typhi after hyperosmotic stress may be one reason why the pathogen performs invading in the distal ileum of human and not in areas of the upper small intestine.

Keywords

• Salmonella enterica serovar Typhi
• hyperosmotic stress
• microarray
• gene expression.