Type VI secretion system sequences in ancient Vbrio cholerae PA1849

The gram-negative bacterium Vibrio cholerae is the causative agent of the diarrhoeal disease cholera and is responsible for seven recorded pandemics. Several factors are postulated to have led to the decline of 6th pandemic classical strains and the rise of El Tor biotype V. cholerae, establishing the current 7th pandemic. The type six secretion system is one mechanism that allows V. cholerae to persist in the environment and the host. We investigated the ability of classical V. cholerae strains of the 2nd and 6th pandemics to engage in microbial competition and tested their immunity against T6SS-mediated attacks. We examined three aspects of competitiveness across pandemic cholera strains: the ability to engage in T6SS battle with commensal bacteria, compete with non-pandemic strains and compete with other pandemic strains. Analysis of available V. cholerae genomes over a timeline spanning 150 years provides insights into the role of T6SS in bacterial competition across pandemics.