During the initial phases of infection, Salmonella Typhimurium uses flagella‑mediated motility to reach the intestinal epithelium and initiate host cell contact. At the infection site, Salmonella employs a type III secretion system (T3SS‑1), encoded in SPI‑1, to secrete effector proteins into the host cytosol that mediate uptake. Expression of these two virulence factors is heterogeneous: only a subset of cells display a motile (flagella‑ON) or invasive (T3SS‑ON) phenotype. How their expression is coordinated at the single‑cell level remains largely uncharacterized.
We use single‑cell analysis of dual fluorescent reporter strains to track flagella and T3SS‑1 expression dynamics in individual bacteria. By comparing wild‑type and mutant strains under varying environmental conditions, we aim to map the regulatory interactions that coordinate virulence gene expression during infection and reveal how external cues shape the single‑cell response.
Kymograph of a dual transcriptional reporter for flagella (cyan) and SPI‑1 (magenta) in cells grown in a mother machine device, showing fluorescence overlays (top) and phase‑contrast images (bottom).