Type III secretion machines: Bacterial devices for protein delivery into host cells

Several Cram-negative pathogenic bacteria have evolved a complex protein se cretion system termed type III to deliver bacterial effector proteins into host cells that then modulate host cellular functions. These bacterial devi ces are present in both plant and animal pathogenic bacteria and are evolut ionarily related to the flagellar apparatus. Although type III secretion sy stems are substantially conserved, the effector molecules they deliver are unique for each bacterial species. Understanding the biology of these devic es may allow the development of novel prevention and therapeutic approaches for several infectious diseases.