Bacterial Transposons—An Increasingly Diverse Group of Elements

Whittle, Gabrielle; Salyers, Abigail A.

doi:10.1002/047122197x.ch17

Cited by 10 publications

(14 citation statements)

References 93 publications

(134 reference statements)

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“…Many steps are required for transfer of conjugative transposons, such as excision from the chromosome, nicking of the OriT, and assembly of the mating bridge (28). To investigate the effect of RteR on excision from the chromosome, we introduced rteR on a plasmid into a strain containing CTnERL.…”

Section: Figmentioning

confidence: 99%

The Small RNA RteR Inhibits Transfer of the Bacteroides Conjugative Transposon CTnDOT

Waters

Salyers

2012

J Bacteriol

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CTnDOT is a 65-kb conjugative transposon present in Bacteroides spp. that confers resistance to erythromycin [ erm (F)] and tetracycline [ tet (Q)]. An interesting feature of CTnDOT is that both excision from the chromosome and transfer of CTnDOT are stimulated by exposure to tetracycline. However, when no tetracycline is present, transfer of CTnDOT is not detectable. Previous studies suggested that a region containing a small RNA, RteR, appeared to mediate repression of CTnDOT transfer; however, virtually nothing was known about RteR. We have demonstrated that RteR is a 90-nucleotide transcript that is not further processed. RteR inhibits conjugative transfer of CTnDOT by targeting the transfer region, a 13-kb operon that encodes the tra genes required to assemble the mating apparatus. We report here that RteR interacts with the region downstream of traA . Levels of the downstream tra mRNA are dramatically reduced when RteR is present. Further, RteR does not appear to decrease the half-life of the tra mRNA transcript, suggesting that RteR does not bind to the transcript to initiate RNase-dependent decay, similar to other trans -acting small RNAs. We predict that RteR may act to enhance termination of the tra operon within traB , which could account for the decreased abundance of the tra transcript downstream of traA and explain why the tra mRNA has the same half-life whether or not RteR is present. RteR is the only small RNA that has been characterized so far within the Bacteroidetes phylum.

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Section: Figmentioning

confidence: 99%

The Small RNA RteR Inhibits Transfer of the Bacteroides Conjugative Transposon CTnDOT

Waters

Salyers

2012

J Bacteriol

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“…CTns range in size from 18 to 500 kb with the majority of CTns averaging roughly 50 to 80 kb. The large size of most CTns is due to the need to encode the entire suite of gene products necessary to facilitate conjugative transfer, such as relaxases, coupling proteins, and mating bridge proteins (29, 30). Interestingly, these elements contain genes reminiscent of transposons, plasmids, and bacteriophages and thus share characteristics with these other mobile DNA elements.…”

Section: Introductionmentioning

confidence: 99%

Regulation of CTnDOT Conjugative Transfer Is a Complex and Highly Coordinated Series of Events

Waters

Salyers

2013

mBio

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CTnDOT is a 65-kb conjugative transposon that is found in Bacteroides spp., which are one of the more abundant members within the lower human gastrointestinal tract. CTnDOT encodes resistance to the antibiotics erythromycin and tetracycline (Tc). An interesting feature of CTnDOT is that exposure to low levels of Tc induces a cascade of events that ultimately results in CTnDOT conjugative transfer. However, Tc is apparently not a switch that activates transfer but rather a signal that appears to override a series of negative regulators that inhibit premature excision and transfer of CTnDOT. In this minireview, we summarize over 20 years of research that focused on elucidating the highly coordinated regulation of excision, mobilization, and transfer of CTnDOT.

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“…The intermediate is nicked at oriT and a single strand is transferred to a recipient cell via conjugation. The DNA is replicated in the recipient cell to form the double stranded circular form, which then integrates into the Bacteroides chromosome (18, 19). CTnDOT is stably maintained even in the absence of selection, perhaps due to the complexity of its regulatory system (19).…”

Section: Introductionmentioning

confidence: 99%

The Integration and Excision of CTnDOT

Wood

Gardner

2015

Microbiol Spectr

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Bacteroides species are one of the most prevalent groups of bacteria present in the human colon. Many strains carry large, integrated elements including integrative and conjugative elements (ICEs). One such ICE is CTnDOT, which is 65 kb in size and encodes resistances to tetracycline and erythromycin. CTnDOT has been increasing in prevalence in Bacteroides spp., and is now found in greater than 80% of natural isolates. In recent years, CTnDOT has been implicated in the spread of antibiotic resistance among gut microbiota. Interestingly, the excision and transfer of CTnDOT is stimulated in the presence of tetracycline. The tyrosine recombinase IntDOT catalyzes the integration and excision reactions of CTnDOT. Unlike the well-characterized lambda Int, IntDOT tolerates heterology in the overlap region between the sites of cleavage and strand exchange. IntDOT also appears to have a different arrangement of active site catalytic residues. It is missing one of the arginine residues that is conserved in other tyrosine recombinases. The excision reaction of CTnDOT is complex, involving excision proteins Xis2c, Xis2d, and Exc, as well as IntDOT and a Bacteroides host factor. Xis2c and Xis2d are small, basic proteins like other recombination directionality factors (RDFs). Exc is a topoisomerase; however, the topoisomerase function is not required for the excision reaction. Exc has been shown to stimulate excision frequencies when there are mismatches in the overlap regions, suggesting that it may play a role in resolving Holliday junctions containing heterology. Work is currently under way to elucidate the complex interactions involved with the formation of the CTnDOT excisive intasomes.

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Bacterial Transposons—An Increasingly Diverse Group of Elements

Cited by 10 publications

References 93 publications

The Small RNA RteR Inhibits Transfer of the Bacteroides Conjugative Transposon CTnDOT

The Small RNA RteR Inhibits Transfer of the Bacteroides Conjugative Transposon CTnDOT

Regulation of CTnDOT Conjugative Transfer Is a Complex and Highly Coordinated Series of Events

The Integration and Excision of CTnDOT

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