title: Gene mobility promotes the spread of resistance in bacterial populations.
abstract: Theory predicts that horizontal gene transfer (HGT) expands the selective conditions under which genes spread in bacterial populations. Whereas vertically inherited genes can only spread by positively selected clonal expansion, mobile genetic elements can drive fixation of genes by infectious HGT. We tested this using populations of Pseudomonas fluorescens and the conjugative mercury resistance (HgR) plasmid pQBR57. HGT expanded the selective conditions allowing the spread of HgR: Chromosomal HgRonly increased in frequency under positive selection, whereas plasmid-encoded HgRreached fixation with or without positive selection. Tracking plasmid dynamics over time revealed that the mode of HgRinheritance varied across mercury environments. Under mercury selection, the spread of HgRwas driven primarily by clonal expansion while in the absence of mercury HgRdynamics were dominated by infectious transfer. Thus, HGT is most likely to drive the spread of resistance genes in environments where resistance is useless.
authors.affiliation: Department of Biology, University of York, York Y010 5DD, UK.
authors.forename: Cagla
authors.initials: C
authors.lastname: Stevenson
authors.affiliation: Department of Biology, University of York, York Y010 5DD, UK.
authors.forename: James Pj
authors.identifier: 0000-0002-4896-4592
authors.initials: JP
authors.lastname: Hall
authors.affiliation: Department of Biology, University of York, York Y010 5DD, UK.
authors.forename: Ellie
authors.identifier: 0000-0002-2050-4631
authors.initials: E
authors.lastname: Harrison
authors.affiliation: Department of Biology, University of York, York Y010 5DD, UK.|Department of Mathematics, University of York, York Y010 5DD, UK.
authors.forename: AJamie
authors.initials: A
authors.lastname: Wood
authors.affiliation: Department of Biology, University of York, York Y010 5DD, UK.
authors.forename: Michael A
authors.identifier: 0000-0003-0362-820X
authors.initials: MA
authors.lastname: Brockhurst
mesh_terms: D024881:Drug Resistance, Bacterial / Q000235:genetics*; D022761:Gene Transfer, Horizontal; D008628:Mercury / Q000633:toxicity*; D010957:Plasmids / Q000235:genetics*; D011551:Pseudomonas fluorescens / Q000187:drug effects* / Q000235:genetics*
chemical_list: D008628:Mercury