Deadly syringes: type VI secretion system activities in pathogenicity and interbacterial competition

Among specialized bacterial secretion systems, the most widespread is the type VI secretion system (T6SS). This transports effector molecules into target cells in a single, cell-contact dependent step. T6SSs are structurally related to the cell-puncturing device of tailed bacteriophages and predicted to function as contractile injection machineries that perforate eukaryotic and prokaryotic target membranes for effector delivery. Activities of T6SSs can play important roles in virulence by modifying the eukaryotic host cytoskeleton through actin crosslinking. They are also efficient weaponry in interbacterial warfare and provide a fitness advantage by hydrolyzing cell walls of opponent bacteria. The role of T6SSs in interbacterial competition might enable pathogens to outcompete commensal bacteria and facilitate host colonization.

► Type VI secretion systems (T6SSs) are contractile injection machines that perforate target membranes.
► T6SS-dependent toxin delivery contributes to pathogenicity by, for example, actin crosslinking.
► T6SSs effectors are efficient weaponry in bacterial warfare by, for example, hydrolyzing cell walls of opponent bacteria.
► T6SSs role in interbacterial virulence might enable pathogens to outcompete commensal bacteria.