A New ESX-1 Substrate in Mycobacterium marinum That Is Required for Hemolysis but Not Host Cell Lysis

Both Mycobacterium tuberculosis , the cause of human tuberculosis (TB), and Mycobacterium marinum , a pathogen of ectotherms, use the ESX-1 secretion system to cause disease. There are many established similarities between the ESX-1 systems in M. tuberculosis and in M. marinum . Yet the two bacteria infect different hosts, hinting at species-specific functions of the ESX-1 system. Our findings demonstrate that MMAR_2894 is a PE protein secreted by the ESX-1 system of M. marinum . We show that MMAR_2894 is required for the optimal secretion of mycobacterial proteins required for disease. Because the MMAR_2894 gene is not conserved in M. tuberculosis , our findings demonstrate that MMAR_2894 may contribute to a species-specific function of the ESX-1 system in M. marinum , providing new insight into how the M. marinum and M. tuberculosis systems differ.