The type VI secretion system (T6SS) is a mechanism of bacterial competition harnessed by some Gram-negative bacterial strains. Protein toxins dispensed by the T6SS illicit a cell lysis response upon injection. Bacteria may survive a T6SS mediated attack if they harbor immunity genes that encode neutralizing proteins corresponding to particular effectors. This project investigates the diversity of these T6SS elements that significantly influence coexistence of bacterial strains within a population in a host.