Biomedical subjects

Vincent Burrus

Publications and source records attributed to Vincent Burrus.

9 recordsLinked to original sources

PubMed2006

The current ICE age: biology and evolution of SXT-related integrating conjugative elements.

SXT is an integrating conjugative element (ICE) that was initially isolated from a 1992 Vibrio cholerae O139 clinical isolate from India. This approximately 100-kb ICE encodes resistance to multiple antibiotics. SXT or closely related ICEs are now present in most clinical and some environmental V. cholerae isolates from Asia and Africa. SXT-related ICEs are not limited to V. cholerae. It is now clear that so-called IncJ elements such as R391 are closely related to SXT. More than 25 members of the SXT/R391 family of ICEs have now been identified in environmental and clinical isolates of diverse species of gamma-proteobacteria worldwide. In this review, we discuss the diversity, evolution and biology of this family of ICEs.

Bacterial Proteins↗

PubMed2006

SXT-related integrating conjugative element in New World Vibrio cholerae.

SXT-related integrating conjugative elements (ICEs) became prevalent in Asian Vibrio cholerae populations after V. cholerae O139 emerged. Here, we describe an SXT-related ICE, ICEVchMex1, in a Mexican environmental V. cholerae isolate. Identification of ICEVchMex1 represents the first description of an SXT-related ICE in the Western Hemisphere. The significant differences between the SXT and ICEVchMex1 genomes suggest that these ICEs have evolved independently.

Conjugation, Genetic↗

PubMed2006

Requirement for Vibrio cholerae integration host factor in conjugative DNA transfer.

The requirement for host factors in the transmission of integrative and conjugative elements (ICEs) has not been extensively explored. Here we tested whether integration host factor (IHF) or Fis, two host-encoded nucleoid proteins, are required for transfer of SXT, a Vibrio cholerae-derived ICE that can be transmitted to many gram-negative species. Fis did not influence the transfer of SXT to or from V. cholerae. In contrast, IHF proved to be required for V. cholerae to act as an SXT donor. In the absence of IHF, V. cholerae displayed a modest defect for serving as an SXT recipient. Surprisingly, SXT integration into or excision from the V. cholerae chromosome, which requires an SXT-encoded integrase related to lambda integrase, did not require IHF. Therefore, the defect in SXT transmission in the V. cholerae IHF mutant is probably not related to IHF's ability to promote DNA recombination. The V. cholerae IHF mutant was also highly impaired as a donor of RP4, a broad-host-range conjugative plasmid. Thus, the V. cholerae IHF mutant appears to have a general defect in conjugation. Escherichia coli IHF mutants were not impaired as donors or recipients of SXT or RP4, indicating that IHF is a V. cholerae-specific conjugation factor.

Bacterial Proteins↗

PubMed2004

Shaping bacterial genomes with integrative and conjugative elements.

Integrative and conjugative elements (ICEs) are self-transmissible mobile genetic elements that are increasingly recognized to contribute to lateral gene flow in prokaryotes. ICEs, like most temperate bacteriophages integrate into the genome and like conjugative plasmids disseminate by conjugative transfer to new hosts. Thought of schematically, the structure of ICEs is similar to that of other types of the mobile elements; ICEs have a backbone composed of three modules ensuring maintenance, dissemination and regulation. This backbone can acquire additional functions probably through the action of insertion sequences, transposons and specific recombinases. Previously, ICEs were thought of as only vectors for transfer of antibiotic resistance genes, but it is now evident that ICEs can mediate the transfer of a very diverse set of functions. ICEs allow bacteria to rapidly adapt to new environmental conditions and to colonize new niches. Like phages and conjugative plasmids they also likely mediate the transfer of virulence determinants. ICEs shape the bacterial genome, promoting variability between strains of the same species and distributing genes between unrelated bacterial genera. Finally, we propose that by utilizing conserved integration sites, ICEs may promote the mobilization of genomic islands.

Attachment Sites, Microbiological↗

PubMed2004

Evolution of genomic islands by deletion and tandem accretion by site-specific recombination: ICESt1-related elements from Streptococcus thermophilus.

The 34 734-bp integrative and potentially conjugative element (putative ICE) ICESt1 has been previously found to be site-specifically integrated in the 3' end of the fda locus of Streptococcus thermophilus CNRZ368. Four types of genomic islands related to ICESt1 are integrated in the same position in seven other strains of S. thermophilus. One of these elements, ICESt3, harbours conjugation and recombination modules closely related to those of ICESt1 and excises by site-specific recombination. Two other types of elements, CIME19258 and CIME302, are flanked by site-specific attachment sites closely related to attL and attR of ICESt1 and ICESt3, whereas Delta CIME308 only possesses a putative attR site; none of these three elements carry complete conjugation and recombination modules. ICESt1 contains a functional internal recombination site, attL', that is almost identical to attL of CIME19258. The recombination between attL' and attR of ICESt1 leads to the excision of the expected circular molecule (putative ICE); a cis-mobilizable element (CIME) flanked by an attL site and an attB' site remains integrated into the 3' end of fda. Furthermore, sequences that could be truncated att sites were found within ICESt1, ICESt3 and CIME302. All together, these data suggest that these genomic islands evolved by deletion and tandem accretion of ICEs and CIMEs resulting from site-specific recombination. A model for this evolution is proposed and its application to other genomic islands is discussed.

Base Sequence↗

PubMed2004

Formation of SXT tandem arrays and SXT-R391 hybrids.

SXT is an integrative and conjugative element (ICE) isolated from Vibrio cholerae. This approximately 100-kb ICE encodes resistance to multiple antibiotics and integrates site specifically into the chromosome. SXT excises from the chromosome to form a circular but nonreplicative extrachromosomal molecule that is required for its transfer. Here we found that a significant fraction of freshly isolated SXT exconjugants contained tandem SXT arrays. There was heterogeneity in the size of the SXT arrays detected in single exconjugant colonies. Some arrays consisted of more than five SXTs arranged in tandem. These extended arrays were unstable and did not persist during serial passages. The mechanism accounting for the generation of SXT arrays is unknown; however, array formation was not dependent upon recA and appeared to depend on conjugative transfer. While such arrays did not alter the transfer frequency of wild-type SXT, they partially complemented the transfer deficiency of a Deltaxis SXT mutant, which is ordinarily unable to generate the extrachromosomal intermediate required for SXT transfer. Exconjugants derived from donor strains that harbored tandem arrays of SXT and R391, an SXT-related element, contained functional hybrid elements that arose from recA-independent recombination between the two ICEs. Thus, arrays of SXT-related elements promote the creation of novel ICEs.

Chromosomes, Bacterial↗

PubMed2003

Control of SXT integration and excision.

The Vibrio cholerae SXT element is a conjugative self-transmissible chromosomally integrating element that encodes resistance to multiple antibiotics. SXT integrates in a site-specific fashion at prfC and excises from the chromosome to form a circular but nonreplicative extrachromosomal form. Both chromosomal integration and excision depend on an SXT-encoded recombinase, Int. Here we found that Int is necessary and sufficient for SXT integration and that int expression in recipient cells requires the SXT activators SetC and SetD. Although no xis-like gene was annotated in the SXT genome, Int was not sufficient to mediate efficient SXT chromosomal excision. We identified a novel SXT Xis that seems to function as a recombination directionality factor (RDF), facilitating SXT excision and inhibiting SXT integration. Although unrelated to any previously characterized RDF, Xis is similar to five hypothetical proteins that together may constitute a new family of RDFs. Using real-time quantitative PCR assays to study SXT excision from the chromosome, we determined that while SXT excision is required for SXT transfer, the percentage of cells containing an excised circular SXT does not appear to be a major factor limiting SXT transfer; i.e., we found that most cells harboring an excised circular SXT molecule do not act as SXT donors. In the absence of prfC, SXT integrated into several secondary attachment sites but preferentially into the 5' end of pntB. SXT excision and transfer from a donor containing pntB::SXT were reduced, suggesting that the SXT integration site may also influence the element's transmissibility.

Amino Acid Sequence↗

PubMed2002

The ICESt1 element of Streptococcus thermophilus belongs to a large family of integrative and conjugative elements that exchange modules and change their specificity of integration.

The 34,734-bp element ICESt1 from Streptococcus thermophilus CNRZ368 is site-specifically integrated into the 3(') end of the gene fda. ICESt1 encodes integrative functions and putative transfer functions. Six proteins of the putative conjugative system of ICESt1 are related to those encoded by the conjugative transposon Tn916 from Enterococcus faecalis. A comparison of these proteins with those encoded by the complete or partial genome sequences of various low G+C bacteria including Bacillus subtilis, Clostridium difficile, E. faecalis, Listeria monocytogenes, Staphylococcus aureus, and Streptococcus mutans revealed the presence of numerous putative site-specific integrative conjugative elements and/or conjugative transposons within these genomes. Sequence comparisons revealed that these elements possess a modular structure and that exchanges of unrelated or distantly related modules and genes have occurred between these elements, and also plasmids and prophages. These exchanges have probably led to modifications in the site specificity of integration of these elements. Therefore, a distinction between low specificity integrative conjugative elements (i.e., conjugative transposons) and site-specific integrative conjugative elements does not appear to be relevant. We propose to call all the conjugative elements that excise by site-specific recombination and integrate by recombination between a specific site of a circular intermediate and another site, "Integrative and Conjugative Elements" (ICEs), irrespective of the integration specificity.

Base Composition↗

PubMed2002

Conjugative transposons: the tip of the iceberg.

Elements that excise and integrate, such as prophages, and transfer by conjugation, such as plasmids, have been found in various bacteria. These elements appear to have a diversified set of characteristics including cell-to-cell contact using pili or cell aggregation, transfer of single-stranded or double-stranded DNA, low or high specificity of integration and serine or tyrosine recombinases. This has led to a highly heterogeneous nomenclature, including conjugative transposons, integrative 'plasmids', genomic islands and numerous unclassified elements. However, all these elements excise by site-specific recombination, transfer the resulting circular form by conjugation and integrate by recombination between a specific site of this circular form and a site in the genome of their host. Whereas replication of the circular form probably occurs during conjugation, this replication is not involved in the maintenance of the element. In this review, we show that these elements share very similar characteristics and, therefore, we propose to classify them as integrative and conjugative elements (ICEs). These elements evolve by acquisition or exchanges of modules with various transferable elements including at least ICEs and plasmids. The ICEs are probably widespread among the bacteria.

Bacteria↗