Protein secretion systems in Mycobacteria

Mycobacteria have a unique cell-envelope structure which protects the bacteria from the extracellular environment by limiting access to noxious molecules from the outside. This extremely hydrophobic and thick barrier also poses a unique problem for the export of bacterial products. Here we review the multiple protein secretion pathways in Mycobacteria, including the general secretion pathway and the Twin-Arginine Transporter, with an emphasis on the ESX-1 alternate secretion system. This newly identified protein secretion system is required for growth during infection and has provided insight into how M. tuberculosis manipulates the host immune response during infection.