title: Environmentally co-occurring mercury resistance plasmids are genetically and phenotypically diverse and confer variable context-dependent fitness effects.
abstract: Plasmids are important mobile elements that can facilitate genetic exchange and local adaptation within microbial communities. We compared the sequences of four co-occurring pQBR family environmental mercury resistance plasmids and measured their effects on competitive fitness of a Pseudomonas fluorescens SBW25 host, which was isolated at the same field site. Fitness effects of carriage differed between plasmids and were strongly context dependent, varying with medium, plasmid status of competitor and levels of environmental mercury. The plasmids also varied widely in their rates of conjugation and segregational loss. We found that few of the plasmid-borne accessory genes could be ascribed functions, although we identified a putative chemotaxis operon, a type IV pilus-encoding cluster and a region encoding putative arylsulfatase enzymes, which were conserved across geographically distant isolates. One plasmid, pQBR55, conferred the ability to catabolize sucrose. Transposons, including the mercury resistance Tn5042, appeared to have been acquired by different pQBR plasmids by recombination, indicating an important role for horizontal gene transfer in the recent evolution of pQBR plasmids. Our findings demonstrate extensive genetic and phenotypic diversity among co-occurring members of a plasmid community and suggest a role for environmental heterogeneity in the maintenance of plasmid diversity.
authors.affiliation: Department of Biology, Wentworth Way, University of York, York, UK.
authors.forename: James P J
authors.initials: JP
authors.lastname: Hall
authors.affiliation: Department of Biology, Wentworth Way, University of York, York, UK.
authors.forename: Ellie
authors.initials: E
authors.lastname: Harrison
authors.affiliation: Pharmaceutical Science Research Division, King's College London, London, UK.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Lilley
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
authors.forename: Steve
authors.initials: S
authors.lastname: Paterson
authors.affiliation: The SIMBIOS Centre, School of Science, Engineering and Technology, Abertay University, Dundee, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Spiers
authors.affiliation: Department of Biology, Wentworth Way, University of York, York, UK.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Brockhurst
mesh_terms: D001192:Arylsulfatases / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004777:Environment; D022761:Gene Transfer, Horizontal; D008628:Mercury / Q000494:pharmacology*; D009876:Operon / Q000235:genetics; D010957:Plasmids / Q000235:genetics*; D011551:Pseudomonas fluorescens / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D012988:Soil Microbiology; D013395:Sucrose / Q000378:metabolism
chemical_list: D004251:DNA Transposable Elements; D013395:Sucrose; D001192:Arylsulfatases; D008628:Mercury