The type VI secretion system (T6SS) is a one step mechanism that is used widely throughout gram-negative bacterial species in injecting effector proteins and virulence factors (such as proteins, toxins, or enzymes) from across the interior (cytoplasm or cytosol) of a bacterial cell into a target cell. T6SS were first identified in 2006, when researchers at Harvard Medical School (Boston, United States) saw that mutations of Hcp and VgrG proteins in Vibrio cholerae led to decreased virulence and infectivity of the pathogen. Soon afterwards, a T6SS was found in Pseudomonas aeruginosa and implicated with Hcp secretion into target cells and chronic infection.