T3SS are highly effective protein secretion machines that can transport their substrates across three membranes in a highly organized and rapid mechanism. I aim to elucidate the actual mechanism of protein secretion, which is still - despite all success in the structural elucidation of the T3SS injectosome – ill defined. To this end, I work on the model SPI-1 T3SS of Salmonella Typhimurium.