The Integration and Excision of CTnDOT

Abstract

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.

Interplay of a non-conjugative integrative element and a conjugative plasmid in the spread of antibiotic resistance via suicidal plasmid transfer from an aquaculture Vibrio isolate

“…coli chromosome, it was designated as a novel integrative element, Tn 6283 , with approval of the Tn number at the transposon registry site ( http://transposon.lstmed.ac.uk/ ). Since the intA product was predicted to possess an extended N-terminus as Lambda Int, the Tn 6283 region may contain motifs conserved in representative ICEs and phages; e.g., an integrase-binding arm-type site, integration host factor (IHF)-binding sites, and Xis-binding regions [ 33 , 34 ]. However, these motifs could not be identified in the Tn 6283 region based on the nucleotide sequence.…”

“…Since Tn 6283 contains two tyrosine recombinase genes, it would be expected to excise itself in the typical ICE circular form [ 34 ]. To precisely define the mobility unit of Tn 6283 , we determined the sequence of the expected recombination joint “ att Tn 6283 ” formed upon excision of the element.…”

In Silico Identification of Three Types of Integrative and Conjugative Elements in Elizabethkingia anophelis Strains Isolated from around the World

“…Several ICEs have been found in the taxa of Bacteroides (42,49,(62)(63)(64), which belong to the family Bacteroidaceae in the phylum Bacteroidetes. Of these elements, CTnDOT in Bacteroides thetaiotaomicron has been studied extensively (39,(65)(66)(67). The ICEs identified in E. anophelis are structurally distinct from CTnDOT.…”

“…The presence of the tfs4 ICE has been associated with virulence, although mechanisms behind the virulence phenotype remain unknown (37). Several ICEs have been identified in taxa of Bacteroides, including CTnDOT (38,39), CTnERL (40,41), and CTnGERM1 (42). In E. anophelis, an ICE named ICEEa1 has been identified in the strains associated with the outbreak in Wisconsin and in unrelated strains from the outbreak in Singapore (43).…”

Multiple serine transposase dimers assemble the transposon-end synaptic complex during IS607-family transposition

“…The tyrosine- and serine-family of recombinases, which have been extensively studied in the context of site-specific recombination reactions, also promote DNA transposition. Respectively, these enzymes splice DNA through a sequential pair of single-strand exchanges or through double strand breaks, generating a transient covalent linkage between the cleaved DNA end and a tyrosine or serine on the protein ( Rubio-Cosials et al, 2018 ; Stark, 2014 ; Wood and Gardner, 2015 ). In this study, we investigate the mechanism by which the IS 607 -family of serine recombinases transpose DNA.…”