Transcriptional adaptation of Shigella flexneri during adherence to epithelial cells

Shigella adhesion to host cells is a transitional stage from an extracellular to an intracellular environment. However, the dynamic adaptations of Shigella during adhesion are poorly understood. To address this, we performed the first transcriptome analysis of Shigella flexneri 2457T during adhesion. A total of 1,757 genes were differentially regulated (>twofold). The majority of plasmid-borne ipa-mxi-spa locus genes were downregulated, indicating these virulence genes were strictly regulated after successful adhesion. Altered expression of genes involved in stress response indicates that adherent S. flexneri encountered envelope stress and oxidative stress. Shigella flexneri also experienced reduced energy production during adherence. Transcript profiling and cell culture assays using glpD and glpK mutants showed that enhancement of glycerol catabolism were related with adhesion ability of S. flexneri. In addition, regulation of expression of some ionic transport system may be required for S. flexneri adhesion. Expression levels of 26 genes were further examined using qRT-PCR, which were congruent with transcriptome data. A comparison with expression profile during intracellular growth revealed major differences in genes involved in translation, surface modification, and utilization of carbon and iron. These results contribute to the knowledge of the adaptation mechanisms of S. flexneri during adhesion.