title: Assessment of Insertion Sequence Mobilization as an Adaptive Response to Oxidative Stress in Acinetobacter baumannii Using IS-seq.
abstract: Insertion sequence (IS) elements are found throughout bacterial genomes and contribute to genome variation by interrupting genes or altering gene expression. Few of the more than 30 IS elements described inAcinetobacter baumanniihave been characterized for transposition activity or expression effects. A targeted sequencing method, IS-seq, was developed to efficiently map the locations of new insertion events inA. baumanniigenomes and was used to identify novel IS sites following growth in the presence of hydrogen peroxide, which causes oxidative stress. Serial subculture in the presence of subinhibitory concentrations of hydrogen peroxide led to rapid selection of cells carrying an ISAba1element upstream of the catalase-peroxidase genekatGSeveral additional sites for the elements ISAba1, ISAba13, ISAba25, ISAba26, and ISAba125were found at low abundance after serial subculture, indicating that each element is active and contributes to genetic variation that may be subject to selection. Following hydrogen peroxide exposure, rapid changes in gene expression were observed in genes related to iron homeostasis. The IS insertions adjacent tokatGresulted in more than 20-fold overexpression of the gene and increased hydrogen peroxide tolerance.IMPORTANCEInsertion sequences (IS) contribute to genomic and phenotypic variation in many bacterial species, but little is known about how transposition rates vary among elements or how selective pressure influences this process. A new method for identifying new insertion locations that arise under experimental growth conditions in the genome, termed IS-seq, was developed and tested with cells grown in the presence of hydrogen peroxide, which causes oxidative stress. Gene expression changes in response to hydrogen peroxide exposure are similar to those observed in other species and include genes that control free iron concentrations. New IS insertions adjacent to a gene encoding a catalase enzyme confirm that IS elements can rapidly contribute to adaptive variation in the presence of selection.
authors.affiliation: J. Craig Venter Institute, La Jolla, California, USA.
authors.forename: Meredith S
authors.initials: MS
authors.lastname: Wright
authors.affiliation: J. Craig Venter Institute, La Jolla, California, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Mountain
authors.affiliation: J. Craig Venter Institute, La Jolla, California, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Beeri
authors.affiliation: J. Craig Venter Institute, La Jolla, California, USA mark.adams@jax.org.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Adams
mesh_terms: D040981:Acinetobacter baumannii / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics; D016680:Genome, Bacterial; D059014:High-Throughput Nucleotide Sequencing / Q000379:methods; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020071:Interspersed Repetitive Sequences; D007501:Iron / Q000378:metabolism; D016254:Mutagenesis, Insertional; D018384:Oxidative Stress
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D006861:Hydrogen Peroxide; D007501:Iron
keywords: Acinetobacter; insertion sequence; mobile genetic elements