Two-component system RgfA/C activates the fbsB gene encoding major fibrinogen-binding protein in highly virulent CC17 clone group B Streptococcus

• Published in: PloS one 2011-02, Vol.6 (2), p.e14658-e14658
• Main Authors: Al Safadi, Rim, Mereghetti, Laurent, Salloum, Mazen, Lartigue, Marie-Frédérique, Virlogeux-Payant, Isabelle, Quentin, Roland, Rosenau, Agnès
• Format: Article
• Language: English
• Subjects: Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacterial Proteins - physiology; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cellular Biology; Clonal deletion; Clone Cells; Cloning; Deletion mutant; Disease; Efficiency; Fibrin; Fibrinogen; Fibrinogen - genetics; Fibrinogen - metabolism; Fibrinogen-binding protein; Gene expression; Gene Expression Regulation, Bacterial; Genes; Gram-positive bacteria; Humans; Immobilized Proteins - metabolism; Infections; Infectious Diseases/Bacterial Infections; Invasiveness; Laboratories; Life Sciences; Listeria; Listeria monocytogenes; Microbiology; Microbiology/Cellular Microbiology and Pathogenesis; Mutagenesis; Mutant Proteins - genetics; Mutant Proteins - metabolism; Mutant Proteins - physiology; Mutants; Neonates; Newborn babies; Organisms, Genetically Modified; Pathogens; Phylogenetics; Plasmids; Protein Binding; Proteins; Regulation; Streptococcus; Streptococcus agalactiae; Streptococcus agalactiae - genetics; Streptococcus agalactiae - metabolism; Streptococcus agalactiae - pathogenicity; Streptococcus infections; Transcription; Transcription (Genetics); Transcription factors; Transcription, Genetic; Virulence - genetics
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0014658

Group B streptococcus (GBS) strains with the highest ability to bind to human fibrinogen belong to the highly invasive clonal complex (CC) 17. To investigate the fibrinogen-binding mechanisms of CC17 strains, we determined the prevalence of fibrinogen-binding genes (fbsA and fbsB), and fbs regulator genes (rogB encoding an fbsA activator, rovS encoding an fbsA repressor and rgf encoding a two-component system [TCS] whose role on fbs genes was not determined yet) in a collection of 134 strains representing the major CCs of the species. We showed that specific gene combinations were related to particular CCs; only CC17 strains contained the fbsA, fbsB, and rgf genes combination. Non polar rgfAC deletion mutants of three CC17 serotype III strains were constructed. They showed a 3.2- to 5.1-fold increase of fbsA transcripts, a 4.8- to 6.7-fold decrease of fbsB transcripts, and a 52% to 68% decreased fibrinogen-binding ability, demonstrating that the RgfA/RgfC TCS inhibits the fbsA gene and activates the fbsB gene. The relative contribution of the two fbs genes in fibrinogen-binding ability was determined by constructing isogenic fbsA, fbsB, deletion mutants of the three CC17 strains. The ability to bind to fibrinogen was reduced by 49% to 57% in ΔfbsA mutants, and by 78% to 80% in ΔfbsB mutants, suggesting that FbsB protein plays a greater role in the fibrinogen-binding ability of CC17 strains. Moreover, the relative transcription level of fbsB gene was 9.2- to 12.7-fold higher than that of fbsA gene for the three wild type strains. Fibrinogen-binding ability could be restored by plasmid-mediated expression of rgfAC, fbsA, and fbsB genes in the corresponding deletion mutants. Thus, our results demonstrate that a specific combination of fbs genes and fbs regulator genes account for the high fibrinogen-binding ability of CC17 strains that may participate to their enhanced invasiveness for neonates as compared to strains of other CCs.