Regulation of a Bacillus subtilis mobile genetic element by intercellular signaling and the global DNA damage response

Horizontal gene transfer contributes to the evolution of bacterial species. Mobile genetic elements play an important role in horizontal gene transfer, and characterization of the regulation of these elements should provide insight into conditions that influence bacterial evolution. We characterized a mobile genetic element, ICEBs1, in the Gram-positive bacterium Bacillus subtilis and found that it is a functional integrative and conjugative element (ICE) capable of transferring to Bacillus and Listeria species. We identified two conditions that promote ICEBs1 transfer: conditions that induce the global DNA damage response and crowding by potential recipients that lack ICEBs1. Transfer of ICEBs1 into cells that already contain the element is inhibited by an intercellular signaling peptide encoded by ICEBs1. The dual regulation of ICEBs1 allows for passive propagation in the host cell until either the potential mating partners lacking ICEBs1 are present or the host cell is in distress.