Characterization of the Bacillus subtilis ESX-­Type Protein Secretion System

Abstract

Esat-6 Protein Secretion Systems are required for the virulence of several human pathogens, most notably Mycobacterium tuberculosis and Staphylococcus aureus. Gene clusters coding for ESX systems have been identified amongst many organisms including the highly tractable non-pathogenic bacterium Bacillus subtilis. In this work, I develop a model system in B. subtilis to study ESX-type Secretion Systems. First, I demonstrate that the B. subtilis yuk/yue locus encodes a functional secretion system. Then, I utilize this system to study the mechanism of protein export. I show that only the N-terminal ATPase domain in the conserved ATPase is essential for substrate export and demonstrate the first evidence of secretion of an intact dimeric complex that requires a composite recognition signal formed by both members of the complex. I also study the function of the B. subtilis ESX system and find that certain yuk mutants have a biofilm phenotype. Finally, I find that the yuk/yue operon is upregulated in the B. subtilis undomesticated strain 3610 and find that none of the Yuk proteins are required for substrate export in this background. Together, these findings help to elucidate the mechanism and function of this important class of secretion systems.