A new flavor of entry exclusion in ICE elements provides a selective advantage for the element and its host

Entry exclusion has been described in many bacterial conjugation systems, but their molecular mechanisms are not well understood. In the current issue, Avello et al. describe a new exclusion system in the conjugative element ICEBs1. They identify the yddJ gene as the functional exclusion gene and its target as the protein product of the conG gene. They provide evidence for a possible mechanism and for the contribution of the system to reduce fitness costs of ICE expression.