title: Identification and characterization of episomal forms of integrative genomic islands in the genus Francisella.
abstract: Recently, we identified a putative prophage on a genomic island (GI) within the genome sequence of Francisella hispaniensis isolate AS0-814 (Francisella tularensis subsp. novicida-like 3523) by the analysis of the CRISPR-Cas systems of Francisella. Various spacer DNAs within the CRISPR region of different F. tularensis subsp. novicida strains were found to be homologous to the putative prophage (Schunder et al., 2013, Int. J. Med. Microbiol. 303:51-60). Now we identified the GI (FhaGI-1) as a mobile element which is able to form a circular episomal structure. The circular episomal form of FhaGI-1 is generated by F. hispaniensis, and the excision of the island is an integrase-dependent and site-specific process. Furthermore, we could demonstrate that the excision of the island is also possible in other bacterial species (Escherichia coli). In addition, we could show that a genetically generated small variant of the island is also functional and, after its electroporation into strain F. tularensis subsp. holarctica LVS, the GI was stable and site-specifically integrated into the genome of the transformants. The integrase is sufficient for the integration and excision of the small variant into and from the DNA backbone, respectively. Thus, the element may be suitable to be used as a genetic tool in F. tularensis research. Furthermore, we identified the tRNA(Val) gene of Francisella as an integration site for GIs. Genomic island FphGI-1 was identified in Francisella philomiragia ATCC 25016. We were not able to detect the episomal form of this GI, probably due to a mutated attR site. However, we could demonstrate that integrative GIs are present in Francisella and that they may allow horizontal gene transfer between different Francisella species.
authors.affiliation: Cellular Interactions of Bacterial Pathogens, Centre for Biological Threats and Special Pathogens, ZBS 2, Robert Koch Institute, Berlin, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Rydzewski
authors.affiliation: Cellular Interactions of Bacterial Pathogens, Centre for Biological Threats and Special Pathogens, ZBS 2, Robert Koch Institute, Berlin, Germany.
authors.forename: Hana
authors.initials: H
authors.lastname: Tlapák
authors.affiliation: Cellular Interactions of Bacterial Pathogens, Centre for Biological Threats and Special Pathogens, ZBS 2, Robert Koch Institute, Berlin, Germany.
authors.forename: Indra P
authors.initials: IP
authors.lastname: Niehaus
authors.affiliation: Centre for Biological Threats and Special Pathogens, Highly Pathogenic Viruses, ZBS 1, Robert Koch Institute, Berlin, Germany.
authors.forename: Piotr W
authors.initials: PW
authors.lastname: Dabrowski
authors.affiliation: Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms, ZBS 2, Robert Koch Institute, Berlin, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Grunow
authors.affiliation: Cellular Interactions of Bacterial Pathogens, Centre for Biological Threats and Special Pathogens, ZBS 2, Robert Koch Institute, Berlin, Germany. Electronic address: HeunerK@rki.de.
authors.forename: Klaus
authors.initials: K
authors.lastname: Heuner
mesh_terms: D004926:Escherichia coli / Q000235:genetics; D005603:Francisella / Q000235:genetics*; D044404:Genomic Islands; D019426:Integrases / Q000235:genetics / Q000378:metabolism; D020071:Interspersed Repetitive Sequences; D010957:Plasmids; D039002:Prophages / Q000235:genetics; D012366:RNA, Transfer, Val / Q000235:genetics; D011995:Recombination, Genetic
chemical_list: D012366:RNA, Transfer, Val; D019426:Integrases
keywords: Bacteriophage; Episomal; Francisella hispaniensis; Francisella tularensis; Genomic island; Horizontal gene transfer; Prophage