Physiological stress of intracellular Shigella flexneri visualized with a metabolic sensor fused to a surface-reporter system.

When deleted of its N-terminal signal-reception domain, the broad host range sigma54-dependent transcriptional regulator XylR, along with its cognate promoter Pu, becomes a sensor of the metabolic stress of the carrier bacteria. We have employed a surface reporter system to visualize the physiological status of intracellular Shigella flexneri during infection of Henle 407 cells in culture. To this end, the xylRDeltaA gene has been engineered adjacent to a bicistronic transcriptional fusion of Pu to a lamB variant tagged with a short viral sequence (cor) and beta-galactosidase (lacZ).