title: TheqacCGene Has Recently Spread between Rolling Circle Plasmids ofStaphylococcus, Indicative of a Novel Gene Transfer Mechanism.
abstract: Resistance ofStaphylococcusspecies to quaternary ammonium compounds, frequently used as disinfectants and biocides, can be attributed toqacgenes. Mostqacgene products belong to the Small Multidrug Resistant (SMR) protein family, and are often encoded by rolling-circle (RC) replicating plasmids. Four classes of SMR-typeqacgene families have been described inStaphylococcusspecies:qacC, qacG, qacJ, andqacH. Within their class, these genes are highly conserved, butqacCgenes are extremely conserved, although they are found in variable plasmid backgrounds. The lower degree of sequence identity of these plasmids compared to the strict nucleotide conservation of theirqacCmeans that this gene has recently spread. In the absence of insertion sequences or other genetic elements explaining the mobility, we sought for an explanation of mobilization by sequence comparison. Publically available sequences ofqacgenes, their flanking genes and the replication gene that is invariably present in RC-plasmids were compared to reconstruct the evolutionary history of these plasmids and to explain the recent spread ofqacC. Here we propose a new model that explains howqacCis mobilized and transferred to acceptor RC-plasmids without assistance of other genes, by means of its location in between the Double Strand replication Origin (DSO) and the Single-Strand replication Origin (SSO). The proposed mobilization model of this DSO-qacC-SSO element represents a novel mechanism of gene mobilization in RC-plasmids, which has also been employed by other genes, such aslnuA(conferring lincomycin resistance). The proposed gene mobility has aided to the wide spread of clinically relevant resistance genes inStaphylococcuspopulations.
authors.affiliation: Molecular Microbiology and Genomics Consultants Zotzenheim, Germany.
authors.forename: Trudy M
authors.initials: TM
authors.lastname: Wassenaar
authors.affiliation: Department of Biomedical Informatics, University of Arkansas for Medical Sciences Little Rock, AR, USA.
authors.forename: David W
authors.initials: DW
authors.lastname: Ussery
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark.
authors.forename: Hanne
authors.initials: H
authors.lastname: Ingmer
keywords: DNA transfer; S. aureus; SMR; evolution; gene mobility; qac; rolling circle plasmids