The type-VI secretion system of the beneficial symbiont .

The mutualistic symbiosis between the Hawaiian bobtail squid and the marine bacterium is a powerful experimental system for determining how intercellular interactions impact animal-bacterial associations. In nature, this symbiosis features multiple strains of within each adult animal, which indicates that different strains initially colonize each squid. Various studies have demonstrated that certain strains of possess a type-VI secretion system (T6SS), which can inhibit other strains from establishing symbiosis within the same host habitat. The T6SS is a bacterial melee weapon that enables a cell to kill adjacent cells by translocating toxic effectors via a lancet-like apparatus. This review describes the progress that has been made in understanding the factors that govern the structure and expression of the T6SS in and its effect on the symbiosis.