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The qacC Gene Has Recently Spread between Rolling Circle Plasmids of Staphylococcus , Indicative of a Novel Gene Transfer Mechanism

View Article: PubMed Central - PubMed

ABSTRACT

Resistance of Staphylococcus species to quaternary ammonium compounds, frequently used as disinfectants and biocides, can be attributed to qac genes. Most qac gene products belong to the Small Multidrug Resistant (SMR) protein family, and are often encoded by rolling-circle (RC) replicating plasmids. Four classes of SMR-type qac gene families have been described in Staphylococcus species: qacC, qacG, qacJ, and qacH. Within their class, these genes are highly conserved, but qacC genes 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 their qacC means 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 of qac genes, 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 of qacC. Here we propose a new model that explains how qacC is 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 as lnuA (conferring lincomycin resistance). The proposed gene mobility has aided to the wide spread of clinically relevant resistance genes in Staphylococcus populations.

No MeSH data available.


Conserved features of the Qac locus. (A) Sequences indicated are highly conserved in the flanks of 25 qacC, qacG, and qacJ genes. (B) Hairpin structure of SSO for QacC plasmids.
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Figure 6: Conserved features of the Qac locus. (A) Sequences indicated are highly conserved in the flanks of 25 qacC, qacG, and qacJ genes. (B) Hairpin structure of SSO for QacC plasmids.

Mentions: Adding sequences of Type I QacC plasmids to the alignment on which Figure 5 was based identified conserved sequences essential for replication, summarized in Figure 6. The distal end of the 165 nt-long QacC upstream flank including the DSO is strictly conserved, though the third base is G instead of T in Type I QacC plasmids only. The direct repeat unit DR1 of QacC plasmids is also present in all QacG plasmids, two QacJ plasmids and in the single QacH plasmid that was analyzed. Besides in QacC plasmids, the DR2 unit is repeated in two QacJ plasmids (the three other QacJ sequences contain an alternative DR2). In all plasmids, the DSO is followed by a stretch of low complexity sequences containing multiple short homo-nucleotide repeats. The rest of the upstream flank is not conserved between these Qac plasmids.


The qacC Gene Has Recently Spread between Rolling Circle Plasmids of Staphylococcus , Indicative of a Novel Gene Transfer Mechanism
Conserved features of the Qac locus. (A) Sequences indicated are highly conserved in the flanks of 25 qacC, qacG, and qacJ genes. (B) Hairpin structure of SSO for QacC plasmids.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5037232&req=5

Figure 6: Conserved features of the Qac locus. (A) Sequences indicated are highly conserved in the flanks of 25 qacC, qacG, and qacJ genes. (B) Hairpin structure of SSO for QacC plasmids.
Mentions: Adding sequences of Type I QacC plasmids to the alignment on which Figure 5 was based identified conserved sequences essential for replication, summarized in Figure 6. The distal end of the 165 nt-long QacC upstream flank including the DSO is strictly conserved, though the third base is G instead of T in Type I QacC plasmids only. The direct repeat unit DR1 of QacC plasmids is also present in all QacG plasmids, two QacJ plasmids and in the single QacH plasmid that was analyzed. Besides in QacC plasmids, the DR2 unit is repeated in two QacJ plasmids (the three other QacJ sequences contain an alternative DR2). In all plasmids, the DSO is followed by a stretch of low complexity sequences containing multiple short homo-nucleotide repeats. The rest of the upstream flank is not conserved between these Qac plasmids.

View Article: PubMed Central - PubMed

ABSTRACT

Resistance of Staphylococcus species to quaternary ammonium compounds, frequently used as disinfectants and biocides, can be attributed to qac genes. Most qac gene products belong to the Small Multidrug Resistant (SMR) protein family, and are often encoded by rolling-circle (RC) replicating plasmids. Four classes of SMR-type qac gene families have been described in Staphylococcus species: qacC, qacG, qacJ, and qacH. Within their class, these genes are highly conserved, but qacC genes 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 their qacC means 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 of qac genes, 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 of qacC. Here we propose a new model that explains how qacC is 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 as lnuA (conferring lincomycin resistance). The proposed gene mobility has aided to the wide spread of clinically relevant resistance genes in Staphylococcus populations.

No MeSH data available.