Bacterial secretion systems: Networks of pathogenic regulation and adaptation in mycobacteria and beyond.

Bacteria transport proteins to diverse intracellular or extracellular locations to ensure proper function. Proteins are localized intracellularly to the cytoplasm or the periplasm or embedded in membranes. Extracellular proteins are localized to the bacterial surface, secreted into the environment, or directly transported into bacterial or host cells. Protein transport systems can be general or specialized. Recently, there have been several advances in our understanding of specialized protein secretion in pathogenic mycobacteria. Here, we will review broad themes across bacterial secretion systems, highlighting that, although gram-negative and Mycobacterial/Gram-positive specialized secretion systems are unrelated, they share conserved themes of regulation and environmental sensing.