Gamma-Mobile-Trio systems are mobile elements rich in bacterial defensive and offensive tools

The evolutionary arms race between bacteria and phages led to the emergence of bacterial immune systems whose diversity and dynamics remain poorly understood. Here we use comparative genomics to describe a widespread genetic element, defined by the presence of the Gamma-Mobile-Trio (GMT) proteins, that serves as a reservoir of offensive and defensive tools. We demonstrate, using Vibrio parahaemolyticus as a model, that GMT-containing genomic islands are active mobile elements. Furthermore, we show that GMT islands’ cargoes contain various anti-phage defence systems, antibacterial type VI secretion system (T6SS) effectors and antibiotic-resistance genes. We reveal four anti-phage defence systems encoded within GMT islands and further characterize one system, GAPS1, showing it is triggered by a phage capsid protein to induce cell dormancy. Our findings underscore the need to broaden the concept of ‘defence islands’ to include defensive and offensive tools, as both share the same mobile elements for dissemination. GMT-containing genomic islands in Vibrio parahaemolyticus and other diverse bacteria serve as a stockpile of immune and anti-phage defence systems, antibiotic-resistance genes and offensive tools such as type VI secretion system effectors.