title: Streptococcal group B integrative and mobilizable element IMESag-rpsI encodes a functional relaxase involved in its transfer.
abstract: Streptococcus agalactiae or Group B Streptococcus (GBS) are opportunistic bacteria that can cause lethal sepsis in children and immuno-compromised patients. Their genome is a reservoir of mobile genetic elements that can be horizontally transferred. Among them, integrative and conjugative elements (ICEs) and the smaller integrative and mobilizable elements (IMEs) primarily reside in the bacterial chromosome, yet have the ability to be transferred between cells by conjugation. ICEs and IMEs are therefore a source of genetic variability that participates in the spread of antibiotic resistance. Although IMEs seem to be the most prevalent class of elements transferable by conjugation, they are poorly known. Here, we have studied a GBS-IME, termed IMESag-rpsI, which is widely distributed in GBS despite not carrying any apparent virulence trait. Analyses of 240 whole genomes showed that IMESag-rpsI is present in approximately 47% of the genomes, has a roughly constant size (approx. 9 kb) and is always integrated at a single location, the 3'-end of the gene encoding the ribosomal protein S9 (rpsI). Based on their genetic variation, several IMESag-rpsI types were defined (A-J) and classified in clonal complexes (CCs). CC1 was the most populated by IMESag-rpsI (more than 95%), mostly of type-A (71%). One CC1 strain (S. agalactiae HRC) was deep-sequenced to understand the rationale underlying type-A IMESag-rpsI enrichment in GBS. Thirteen open reading frames were identified, one of them encoding a protein (MobSag) belonging to the broadly distributed family of relaxases MOBV1Protein MobSag was purified and, by a newly developed method, shown to cleave DNA at a specific dinucleotide. The S. agalactiae HRC-IMESag-rpsI is able to excise from the chromosome, as shown by the presence of circular intermediates, and it harbours a fully functional mobilization module. Further, the mobSag gene encoded by this mobile element is able to promote plasmid transfer among pneumococcal strains, suggesting that MobSag facilitates the spread of IMESag-rpsI and that this spread would explain the presence of the same IMESag-rpsI type in GBS strains belonging to different CCs.
authors.affiliation: Departamento de Bioquímica, Microbiología, Biología Celular y Genética, Instituto Universitario de Enfermedades Tropicales y Salud Pública de Canarias, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez s/n, 38071 Santa Cruz de Tenerife, Spain Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain.
authors.forename: Fabian
authors.initials: F
authors.lastname: Lorenzo-Diaz
authors.affiliation: Centro de Investigaciones Biológicas, CSIC, Madrid, Spain.
authors.forename: Cris
authors.initials: C
authors.lastname: Fernández-Lopez
authors.affiliation: Institut Pasteur, Unité Ecologie et Evolution de la Résistance aux Antibiotiques, Paris CNRS UMR3525, France.
authors.forename: Pierre-Emmanuel
authors.initials: PE
authors.lastname: Douarre
authors.affiliation: Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge, UK.
authors.forename: Adrian
authors.initials: A
authors.lastname: Baez-Ortega
authors.affiliation: Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Flores
authors.affiliation: Institut Pasteur, Unité Ecologie et Evolution de la Résistance aux Antibiotiques, Paris CNRS UMR3525, France pglaser@pasteur.fr.
authors.forename: Philippe
authors.initials: P
authors.lastname: Glaser
authors.affiliation: Centro de Investigaciones Biológicas, CSIC, Madrid, Spain mespinosa@cib.csic.es.
authors.forename: Manuel
authors.identifier: 0000-0003-3958-0543
authors.initials: M
authors.lastname: Espinosa
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002876:Chromosomes, Bacterial / Q000235:genetics; D003001:Cloning, Molecular / Q000379:methods*; D004254:DNA Nucleotidyltransferases / Q000235:genetics* / Q000378:metabolism; D022761:Gene Transfer, Horizontal; D014644:Genetic Variation; D020071:Interspersed Repetitive Sequences; D016366:Open Reading Frames; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins / Q000235:genetics; D017422:Sequence Analysis, DNA; D013292:Streptococcus agalactiae / Q000201:enzymology / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins; D004254:DNA Nucleotidyltransferases; C110340:DNA relaxase
keywords: Streptococcus; conjugation; horizontal gene transfer; integrative and mobilizable elements mobilization; relaxases