Activation of aVibrio choleraeCBASS anti-phage system by quorum sensing and folate depletion

Abstract

AbstractA major challenge faced by bacteria is infection by bacteriophage (phage). Abortive infection is one strategy for combating phage in which an infected cell kills itself to limit phage replication, thus protecting neighboring kin. One class of abortive infection systems is thecyclic oligonucleotidebasedanti-phagesignalingsystem (CBASS) which relies on two core enzymatic activities; an oligo-nucleotide cyclase that is activated following phage infection and a cyclic-oligo-nucleotide sensitive effector whose activity kills the infected cell. However, the mechanisms behind the deployment and activation of these lethal CBASS systems prior-to and following infection have largely remained a mystery. While exploring unique genomic features of the current pandemicVibrio choleraebiotype El Tor for clues underlying its pandemic success we found its CBASS was spuriously activated by the folate biosynthesis inhibitor sulfamethoxazole, but only after the population had reached a high-cell density. This population density dependent activity revealed that transcription of both the oligo-nucleotide cyclase,dncV, and the CBASS phospholipase effector,capV, is enhanced at high-cell density by quorum sensing. Together, these results demonstrate that theV. choleraeCBASS is deployed when the environment is densely populated and activated in response to a perturbation in folate biosynthesis.SignificanceTo counteract infection with phage, bacteria have evolved a myriad of molecular defense systems. Some of these systems initiate a process called abortive infection, in which the infected cell kills itself to prevent phage propagation. However, such systems must be inhibited in the absence of phage infection to prevent spurious death of the host. Here we show that thecyclic oligonucleotidebasedanti-phagesignalingsystem (CBASS) accomplishes this by sensing intracellular folate molecules and only expressing this system in a group. These results enhance our understanding of the evolution of the 7thV. choleraepandemic and more broadly how bacteria defend themselves against phage infection.