Manganese scavenging and oxidative stress response mediated by type VI secretion system in Burkholderia thailandensis
Significance As an essential micronutrient, Gram-negative bacteria must concentrate Mn 2+ into the cytosol via active transport systems to meet cellular demands. Whereas inner membrane Mn 2+ transporters have been characterized, an active transporter for translocation of Mn 2+ across the outer membrane has not been described. Here we report a Mn 2+ -scavenging pathway consisting of a newly identified TonB-dependent outer membrane manganese transporter, MnoT, and a type VI secretion system (T6SS)-secreted Mn 2+ -binding protein, TseM. Traditionally, T6SS is recognized as a contact-dependent nanomachine to inject effectors into eukaryotic or prokaryotic cells for virulence or for interbacterial competition. The contact-independent functions of T6SS for metal acquisition and bacteria–bacteria competition, reported here, suggest that T6SS may have been retrofitted by some bacteria to gain additional adaptive functions during evolution.