A bistable orthogonal prokaryotic differentiation system underlying development of conjugative transfer competence

The mechanisms and impact of horizontal gene transfer processes to distribute gene functions with potential adaptive benefit among prokaryotes have been well documented. In contrast, little is known about the life-style of mobile elements mediating horizontal gene transfer, whereas this is the ultimate determinant for their transfer fitness. Here, we investigate the life-style of an integrative and conjugative element (ICE) within the genus Pseudomonas that stands model for a widespread family transmitting genes for xenobiotic compound metabolism and antibiotic resistances. The ICE only transfers from a small fraction of cells in a population, which we uncover here, results from a dedicated transfer competence program imposed by the ICE. Transfer competence is orthogonally maintained in individual cells in which it is activated, making them the centerpiece of ICE conjugation. The components mediating transfer competence are widely conserved, underscoring their selected fitness for efficient transfer of this class of mobile elements.