The Role of Type VI Secretion System Effectors in Target Cell Lysis and Subsequent Horizontal Gene Transfer.

Bacteria use type VI secretion systems (T6SSs) to manipulate host cells during pathogenesis or to kill competing bacteria, which, in some cases, increases horizontal gene transfer. These functions largely depend on T6SS regulation, dynamics, and the set of effectors that the system delivers into the target cells. Here, we show that Acinetobacter baylyi ADP1 assembles a highly dynamic T6SS capable of killing and lysing bacterial cells. T6SS function depends on conserved T6SS components as well as Acinetobacter-specific genes of unknown function. Five different effectors, encoded next to VgrG or PAAR proteins and their cognate immunity proteins, cause distinct changes in the prey cells, resulting in various degrees of their lysis. Prey lysis correlates with the rate of DNA transfer from prey to predator, suggesting that lytic effectors are required for efficient T6SS-dependent horizontal gene transfer in naturally competent bacteria.