title: Silencing quorum sensing and ICE mobility through antiactivation and ribosomal frameshifting.
abstract: Mobile genetic elements run an evolutionary gauntlet to maintain their mobility in the face of selection against their selfish dissemination but, paradoxically, they can accelerate the adaptability of bacteria through the gene-transfer events that they facilitate. These temporally conflicting evolutionary forces have shaped exquisite regulation systems that silence mobility and maximize the competitive fitness of the host bacterium, but maintain the ability of the element to deliver itself to a new host should the opportunity arise. Here we review the excision regulation system of theMesorhizobium lotisymbiosis island ICEMlSymR7A, a 502-kb integrative and conjugative element (ICE) capable of converting non-symbiotic mesorhizobia into plant symbionts. ICEMlSymR7Aexcision is activated by quorum sensing, however, both quorum sensing and excision are strongly repressed in the vast majority of cells by dual-target antiactivation and programmed ribosomal-frameshifting mechanisms. We examine these recently discovered regulatory features under the light of natural selection and discuss common themes that can be drawn from recent developments in ICE biology.
authors.affiliation: School of Biomedical Sciences; Curtin University ; Perth, Australia.
authors.forename: Joshua P
authors.initials: JP
authors.lastname: Ramsay
authors.affiliation: Department of Microbiology and Immunology; University of Otago ; Dunedin, New Zealand.
authors.forename: Clive W
authors.initials: CW
authors.lastname: Ronson
keywords: ICE; T4SS; acyl homoserine lactone; antiactivation; bet-hedging; bistability; excisionase; integrase; integrative and conjugative elements; nitrogen fixation; programmed ribosomal frameshifting; quorum sensing; recoding; rhizobia; rolling-circle replication; secretion; symbiosis; synthetic biology