title: Natural Mutations in Streptococcus agalactiae Resulting in Abrogation of β Antigen Production.
abstract: Streptococcus agalactiae genome encodes 21 two-component systems (TCS) and a variety of regulatory proteins in order to control gene expression. One of the TCS, BgrRS, comprising the BgrR DNA-binding regulatory protein and BgrS sensor histidine kinase, was discovered within a putative virulence island. BgrRS influences cell metabolism and positively control the expression of bac gene, coding for β antigen at transcriptional level. Inactivation of bgrR abrogated bac gene expression and increased virulence properties of S. agalactiae. In this study, a total of 140 strains were screened for the presence of bac gene, and the TCS bgrR and bgrS genes. A total of 53 strains carried the bac, bgrR and bgrS genes. Most of them (48 strains) expressed β antigen, while five strains did not express β antigen. Three strains, in which bac gene sequence was intact, while bgrR and/or bgrS genes had mutations, and expression of β antigen was absent, were complemented with a constructed plasmid pBgrRS(P) encoding functionally active bgrR and bgrS gene alleles. This procedure restored expression of β antigen indicating the crucial regulatory role of TCS BgrRS. The complemented strain A49V/BgrRS demonstrated attenuated virulence in intraperitoneal mice model of S. agalactiae infection compared to parental strain A49V. In conclusion we showed that disruption of β antigen expression is associated with: i) insertion of ISSa4 upstream the bac gene just after the ribosomal binding site; ii) point mutation G342A resulting a stop codon TGA within the bac gene and a truncated form of β antigen; iii) single deletion (G) in position 439 of the bgrR gene resulting in a frameshift and the loss of DNA-binding domain of the BgrR protein, and iv) single base substitutions in bgrR and bgrS genes causing single amino acid substitutions in BgrR (Arg187Lys) and BgrS (Arg252Gln). The fact that BgrRS negatively controls virulent properties of S. agalactiae gives a novel clue for understanding of S. agalactiae adaptation to the human.
authors.affiliation: Department of Molecular Microbiology, Institute of Experimental Medicine, Saint-Petersburg, Russia.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Vasilyeva
authors.affiliation: Department of Life Sciences, Centro de Recursos Microbiológicos (CREM) and Research Unit on Applied Molecular Biosciences (UCIBIO, REQUIMTE), Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal.
authors.forename: Ilda
authors.initials: I
authors.lastname: Santos Sanches
authors.affiliation: Department of Infectious Diseases, National Institute of Health, Lisbon, Portugal.
authors.forename: Carlos
authors.initials: C
authors.lastname: Florindo
authors.affiliation: Department of Molecular Microbiology, Institute of Experimental Medicine, Saint-Petersburg, Russia; Department of Fundamental Problems of Medicine and Medical Technologies, Saint-Petersburg State University, Saint-Petersburg, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Dmitriev
mesh_terms: D000818:Animals; D000941:Antigens / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D000071677:Histidine Kinase; D006801:Humans; D051379:Mice; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013290:Streptococcal Infections / Q000473:pathology / Q000662:veterinary; D013292:Streptococcus agalactiae / Q000235:genetics* / Q000378:metabolism* / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics
chemical_list: D000941:Antigens; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D011494:Protein Kinases; D000071677:Histidine Kinase