title: The chromosomal SezAT toxin-antitoxin system promotes the maintenance of the SsPI-1 pathogenicity island in epidemic Streptococcus suis.
abstract: Streptococcus suis has emerged as a causative agent of human meningitis and streptococcal toxic shock syndrome over the last years. The high pathogenicity of S. suis may be due in part to a laterally acquired pathogenicity island (renamed SsPI-1), which can spontaneously excise and transfer to recipients. Cells harboring excised SsPI-1 can potentially lose this island if cell division occurs prior to its reintegration; however, attempts to cure SsPI-1 from the host cells have been unsuccessful. Here, we report that an SsPI-1-borne Epsilon/Zeta toxin-antitoxin system (designated SezAT) promotes SsPI-1 stability in bacterial populations. The sezAT locus consists of two closely linked sezT and sezA genes encoding a toxin and its cognate antitoxin, respectively. Overproduction of SezT induces a bactericidal effect that can be neutralized by co-expression of SezA, but not by its later action. When devoid of a functional SezAT system, large-scale deletion of SsPI-1 is straightforward. Thus, SezAT serves to ensure inheritance of SsPI-1 during cell division, which may explain the persistence of epidemic S. suis. This report presents the first functional characterization of TA loci in S. suis, and the first biochemical evidence for the adaptive significance of the Epsilon/Zeta system in the evolution of pathogen virulence.
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Xinyue
authors.initials: X
authors.lastname: Yao
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Tian
authors.initials: T
authors.lastname: Chen
authors.affiliation: Department of Biochemistry and Molecular Biology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Shen
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Min
authors.initials: M
authors.lastname: Wang
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Xiancai
authors.initials: X
authors.lastname: Rao
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Supeng
authors.initials: S
authors.lastname: Yin
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Yali
authors.initials: Y
authors.lastname: Gong
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Shuguang
authors.initials: S
authors.lastname: Lu
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Le
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Yinling
authors.initials: Y
authors.lastname: Tan
authors.affiliation: PLA Research Institute of Clinical Laboratory Medicine, Nanjing General Hospital of Nanjing Military Command, Nanjing, 210002, China.
authors.forename: Jiaqi
authors.initials: J
authors.lastname: Tang
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Hu
authors.initials: H
authors.lastname: Fuquan
authors.affiliation: Department of Microbiology, Third Military Medical University, Chongqing, 400038, China.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
mesh_terms: D000992:Antitoxins / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D001427:Bacterial Toxins / Q000235:genetics*; D002876:Chromosomes, Bacterial; D044404:Genomic Islands; D006801:Humans; D013290:Streptococcal Infections / Q000382:microbiology; D017011:Streptococcus suis / Q000235:genetics* / Q000472:pathogenicity*; D014774:Virulence / Q000235:genetics
chemical_list: D000992:Antitoxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins