Type 1 and 5 secretion systems and associated toxins

Many virulence factors of Escherichia coli need to traverse the inner membrane, periplasm, and outer membrane to be effective. The bacterium has a variety of secretion systems to achieve this. Two of these, the type I secretion system (T1SS) and the type V secretion system (T5SS), are explored in this chapter. In E. coli the best-known T1SS is that used to secrete hemolysin, a pore-forming toxin found in both uropathogenic and enterohemorrhagic strains of E. coli. Many proteins are secreted via the T5SS in E. coli, with the proteins having a wide range of virulence functions. This chapter will focus on these two systems; the mechanism of biogenesis, the function of the secreted proteins and current attempts to use these systems in biotechnological applications.