title: A Locus Encoding Variable Defense Systems against Invading DNA Identified in Streptococcus suis.
abstract: Streptococcus suis, an important zoonotic pathogen, is known to have an open pan-genome and to develop a competent state. In S. suis, limited genetic lineages are suggested to be associated with zoonosis. However, little is known about the evolution of diversified lineages and their respective phenotypic or ecological characteristics. In this study, we performed comparative genome analyses of S. suis, with a focus on the competence genes, mobile genetic elements, and genetic elements related to various defense systems against exogenous DNAs (defense elements) that are associated with gene gain/loss/exchange mediated by horizontal DNA movements and their restrictions. Our genome analyses revealed a conserved competence-inducing peptide type (pherotype) of the competence system and large-scale genome rearrangements in certain clusters based on the genome phylogeny of 58 S. suis strains. Moreover, the profiles of the defense elements were similar or identical to each other among the strains belonging to the same genomic clusters. Our findings suggest that these genetic characteristics of each cluster might exert specific effects on the phenotypic or ecological differences between the clusters. We also found certain loci that shift several types of defense elements in S. suis. Of note, one of these loci is a previously unrecognized variable region in bacteria, at which strains of distinct clusters code for different and various defense elements. This locus might represent a novel defense mechanism that has evolved through an arms race between bacteria and invading DNAs, mediated by mobile genetic elements and genetic competence.
authors.affiliation: Division of Bacterial and Parasitic Diseases, National Institute of Animal Health, National Agriculture and Food Research Organization, Tsukuba, Japan.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Okura
authors.affiliation: Department of Microbiology, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nozawa
authors.affiliation: Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan.
authors.forename: Takayasu
authors.initials: T
authors.lastname: Watanabe
authors.affiliation: Department of Microbiology, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Murase
authors.affiliation: Department of Microbiology, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Nakagawa
authors.affiliation: Division of Bacterial and Parasitic Diseases, National Institute of Animal Health, National Agriculture and Food Research Organization, Tsukuba, Japan.|The United Graduate School of Veterinary Sciences, Gifu University, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Takamatsu
authors.affiliation: Division of Bacterial and Parasitic Diseases, National Institute of Animal Health, National Agriculture and Food Research Organization, Tsukuba, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Osaki
authors.affiliation: Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Sekizaki
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de Médecine Vétérinaire, Université de Montréal, St-Hyacinthe, Quebec, Canada.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Gottschalk
authors.affiliation: Research Institute for Microbial Diseases, Thailand-Japan Collaboration Center for Emerging and Re-emerging Infections, Osaka University, Suita-Osaka, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Hamada
authors.affiliation: Department of Microbiology, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Fumito
authors.initials: F
authors.lastname: Maruyama
keywords: 
            Streptococcus suis
          ; bacterial defense systems; competence system; mobile genetic elements