Figure 1. Generation and phenotypic characterization of ΔmreC mutants of S. Typhimurium. Schematic representation of wild-type S. Typhimurium expressing the invasion-associated SPI-1 T3SS, flagella for motility and the SPI-2 T3SS essential for intracellular survival. Wild-type Salmonella cells express 1–2 polar SPI-2 needles and approximately 6–8 flagella and SPI-1 needles, distributed predominantly along the lateral cell wall (Bulmer et al., PLoS Pathog 2012). Putative peptidoglycan synthetic complexes comprising the MreBCD cytoskeletal proteins, cell shape-determinants and peptidoglycan synthetic enzymes, are shown as short dynamic complexes moving perpendicularly to the long-axis of the cell. Upon MreC or MreD depletion S. Typhimurium formed spherical cells, with a loss of SPI-1 T3SS and flagella expression; SPI-2 expression remained active. SPI-1 T3SS and flagella expression were restored upon recovery of either mre, hilA (SPI-1 master regulator) or flhDC (flagella master regulator) expression respectively, or with the inactivation of rcsC, sensor kinase of the Rcs phosphorelay envelope stress response.