title: Exploring the evolutionary dynamics of plasmids: the Acinetobacter pan-plasmidome.
abstract: BACKGROUND
  Prokaryotic plasmids have a dual importance in the microbial world: first they have a great impact on the metabolic functions of the host cell, providing additional traits that can be accumulated in the cell without altering the gene content of the bacterial chromosome. Additionally and/or alternatively, from a genome perspective, plasmids can provide a basis for genomic rearrangements via homologous recombination and so they can facilitate the loss or acquisition of genes during these events, which eventually may lead to horizontal gene transfer (HGT). Given their importance for conferring adaptive traits to the host organisms, the interest in plasmid sequencing is growing and now many complete plasmid sequences are available online.
  
  
  RESULTS
  By using the newly developed Blast2Network bioinformatic tool, a comparative analysis was performed on the plasmid and chromosome sequence data available for bacteria belonging to the genus Acinetobacter, an ubiquitous and clinically important group of gamma-proteobacteria. Data obtained showed that, although most of the plasmids lack mobilization and transfer functions, they have probably a long history of rearrangements with other plasmids and with chromosomes. Indeed, traces of transfers between different species can be disclosed.
  
  
  CONCLUSIONS
  We show that, by combining plasmid and chromosome similarity, identity based, network analysis, an evolutionary scenario can be described even for highly mobile genetic elements that lack extensively shared genes. In particular we found that transposases and selective pressure for mercury resistance seem to have played a pivotal role in plasmid evolution in Acinetobacter genomes sequenced so far.
authors.affiliation: Laboratory of Microbial and Molecular Evolution, Dept, of Evolutionary Biology, Via Romana 17-19, University of Florence, I-50125 Florence, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Fondi
authors.forename: Giovanni
authors.initials: G
authors.lastname: Bacci
authors.forename: Matteo
authors.initials: M
authors.lastname: Brilli
authors.forename: Maria Cristiana
authors.initials: MC
authors.lastname: Papaleo
authors.forename: Alessio
authors.initials: A
authors.lastname: Mengoni
authors.forename: Mario
authors.initials: M
authors.lastname: Vaneechoutte
authors.forename: Lenie
authors.initials: L
authors.lastname: Dijkshoorn
authors.forename: Renato
authors.initials: R
authors.lastname: Fani
mesh_terms: D000150:Acinetobacter / Q000235:genetics*; D002876:Chromosomes, Bacterial; D016000:Cluster Analysis; D055028:Comparative Genomic Hybridization; D019295:Computational Biology; D004269:DNA, Bacterial / Q000235:genetics; D019143:Evolution, Molecular; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D010802:Phylogeny; D010957:Plasmids / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial