Mobile integrons encode phage defense systems

Abstract

Integrons are bacterial genetic elements that capture, stockpile,and modulate the expression of genes encoded in integroncassettes. Mobile integrons (MIs) are borne on plasmids, actingas a vehicle for hundreds of antimicrobial resistance genesamong key pathogens. These elements also carry genecassettes of unknown function (gcus) whose role and adaptivevalue remain unexplored. In this work, we show that gcusencode phage resistance systems, many of which are newlydiscovered. Bacteriophage resistance integron cassettes(BRiCs) can be combined and mixed with resistance cassettesto produce multiphage or drug and phage resistance. Thefitness costs of BRiCs are variable and dependent on thegenetic context and can be modulated by changing the order ofcassettes in the array. Hence, MIs act as highly mobile, low-costdefense islands.