An integrative and conjugative element encodes an abortive infection system to protect host cells from predation by a bacteriophage

Abstract

AbstractBacteriophages and integrative and conjugative elements (ICEs, a.k.a. conjugative transposons) are mobile genetic elements that can move from one bacterial cell to another and often coexist in a host genome. Many bacterial species contain at least one temperate (lysogenic) phage and an integrative and conjugative element. Most strains ofBacillus subtilisare lysogenic for the phage SPß and also contain the integrative and conjugative element ICEBs1. We found that the presence of ICEBs1in cells inhibited production of SPß, during both activation of a lysogen and followingde novoinfection. The ICEBs1geneyddK (renamedspbKfor SPß killing) was both necessary and sufficient for the anti-SPß activity. Co-expression ofspbKandyonE, in the absence of other ICEBs1and SPß genes, resulted in inhibition of cell growth and loss of cell viability. These results indicate that togetherspbKandyonEaffected a host process needed for normal growth and thatspbKconstitutes an abortive infection system. We found that this anti-SPß phenotype protected populations ofB. subtilisfrom predation by SPß, likely providing selective pressure for the maintenance of ICEBs1inB. subtilispopulations. spbKencodes a TIR (Toll-interleukin-1 receptor)-domain protein with similarity to both plant antiviral proteins and animal innate immune signaling proteins. We postulate that selective many uncharacterized cargo genes in ICEs may confer selective advantage to cells by protecting against other mobile elements.