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“Background Integrative Conjugative Elements (ICEs) carry functional modules involved in their conjugative transfer, chromosomal integration and for control of expression of ICE genes [1]. ICEs are maintained in their host via site-specific integration and establishment at a unique site or sites in their host [2–7]. ICEs have been discovered in the genomes of find more various low G+C Gram-positive bacteria, various α, β- and γ-Proteobacteria, learn more and Bacteroides species [8]. The first ICE found was
Tn916 from Bacteroides species [8]. One of the best models of ICEs is a family of elements called the R391\SXT family that are found in γ-Proteobacteria. These are interesting elements as over 25 have been found to date in organisms spread across the world. They share a common core scaffold of genes related to integration, excision, transfer and regulation. Different elements can possess different fitness determinants such as antibiotic resistances, heavy metal resistances, and error-prone DNA repair systems [9]. Tn4371 is a 55-kb ICE, which allows its host to degrade biphenyl and 4-chlorobiphenyl. It was isolated after mating between Cupriavidus oxalaticus (Ralstonia oxalatica) A5 carrying the EPZ015938 in vivo broad-host-range
conjugative plasmid RP4 and Cupriavidus metallidurans (Ralstonia metallidurans) CH34. Selection was applied for transconjugants that expressed the heavy metal resistances from CH34 and grew with biphenyl as a sole source of carbon Sclareol and energy [10]. The transconjugants carried an RP4 plasmid with a 55-kb insert near its tetracycline resistance operon. The insert was shown to transpose to other locations and hence was called Tn4371 [10–12]. Tn4371 has been sequenced [13] and closely related elements have been found in the genome sequences of a number of bacteria including Ralstonia
solanacearum GMI1000, a phytopathogen from French Guyana [14], Cupriavidus metallidurans CH34, a heavy metal resistant bacteria from Belgium [15], Erwinia chrysanthemi 3937, aphytopathogen [16] and Azotobacter vinelandii AvOP, a nitrogen-fixing bacterium isolated from soil in the USA [13, 17]. None of these other elements possessed the biphenyl and 4-chlorobiphenyl degradation genes. The Tn4371-like ICEs characterised to date are mosaic in structure consisting of Ti-RP4-like transfer systems, an integrase region, plasmid maintenance genes and accessory genes [13]. All the characterised elements integrate into sites on the bacterial genomes with a conserved 5′-TTTTTCAT-3′ sequence, termed the attB site [11]. Tn4371 transposition most likely involves a site-specific integration/excision process, since the ends of the element can be detected covalently linked as a transfer intermediate [11, 13]. Integration is catalysed by a tyrosine based site specific recombinase related to bacteriophage and ICE family integrases [18].