title: Evolution of genomic islands by deletion and tandem accretion by site-specific recombination: ICESt1-related elements from Streptococcus thermophilus.
abstract: 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.
authors.affiliation: Laboratoire de Génétique et Microbiologie (UMR INRA-UHP no. 1128, IFR no. 110), Faculté des Sciences, Université Henri Poincaré (Nancy 1), BP239, 54506 Vandœuvre-lès-Nancy, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Pavlovic
authors.affiliation: Laboratoire de Génétique et Microbiologie (UMR INRA-UHP no. 1128, IFR no. 110), Faculté des Sciences, Université Henri Poincaré (Nancy 1), BP239, 54506 Vandœuvre-lès-Nancy, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Burrus
authors.affiliation: Laboratoire de Génétique et Microbiologie (UMR INRA-UHP no. 1128, IFR no. 110), Faculté des Sciences, Université Henri Poincaré (Nancy 1), BP239, 54506 Vandœuvre-lès-Nancy, France.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Gintz
authors.affiliation: Laboratoire de Génétique et Microbiologie (UMR INRA-UHP no. 1128, IFR no. 110), Faculté des Sciences, Université Henri Poincaré (Nancy 1), BP239, 54506 Vandœuvre-lès-Nancy, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Decaris
authors.affiliation: Laboratoire de Génétique et Microbiologie (UMR INRA-UHP no. 1128, IFR no. 110), Faculté des Sciences, Université Henri Poincaré (Nancy 1), BP239, 54506 Vandœuvre-lès-Nancy, France.
authors.forename: Gérard
authors.initials: G
authors.lastname: Guédon
mesh_terms: D001483:Base Sequence; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000032:analysis; D019143:Evolution, Molecular; D017353:Gene Deletion; D016680:Genome, Bacterial; D008969:Molecular Sequence Data; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA; D013291:Streptococcus / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements; D004269:DNA, Bacterial