title: Regulation of PI-2b Pilus Expression in Hypervirulent Streptococcus agalactiae ST-17 BM110.
abstract: The widely spread Streptococcus agalactiae (also known as Group B Streptococcus, GBS) "hypervirulent" ST17 clone is strongly associated with neonatal meningitis. The PI-2b locus is mainly found in ST17 strains but is also present in a few non ST17 human isolates such as the ST-7 prototype strain A909. Here, we analysed the expression of the PI-2b pilus in the ST17 strain BM110 as compared to the non ST17 A909. Comparative genome analyses revealed the presence of a 43-base pair (bp) hairpin-like structure in the upstream region of PI-2b operon in all 26 ST17 genomes, which was absent in the 8 non-ST17 strains carrying the PI-2b locus. Deletion of this 43-bp sequence in strain BM110 resulted in a 3- to 5-fold increased transcription of PI-2b. Characterization of PI-2b promoter region in A909 and BM110 strains was carried out by RNAseq, primer extension, qRT-PCR and transcriptional fusions with gfp as reporter gene. Our results indicate the presence of a single promoter (Ppi2b) with a transcriptional start site (TSS) mapped 37 bases upstream of the start codon of the first PI-2b gene. The large operon of 16 genes located upstream of PI-2b codes for the group B carbohydrate (also known as antigen B), a major constituent of the bacterial cell wall. We showed that the hairpin sequence located between antigen B and PI-2b operons is a transcriptional terminator. In A909, increased expression of PI-2b probably results from read-through transcription from antigen B operon. In addition, we showed that an extended 5' promoter region is required for maximal transcription of gfp as a reporter gene in S. agalactiae from Ppi2b promoter. Gene reporter assays performed in Lactococcus lactis strain NZ9000, a related non-pathogenic Gram-positive species, revealed that GBS-specific regulatory factors are required to drive PI-2b transcription. PI-2b expression is up-regulated in the BM110ΔcovR mutant as compared to the parental BM110 strain, but this effect is probably indirect. Collectively, our results indicate that PI-2b expression is regulated in GBS ST17 strains, which may confer a selective advantage in the human host either by reducing host immune responses and/or increasing their dissemination potential.
authors.affiliation: Institut Pasteur, Biology of Gram-positive Pathogens Unit, Paris, France.|Centre National de la Recherche Scientifique (CNRS) ERL3526, Paris, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Périchon
authors.affiliation: Institut Pasteur, Biology of Gram-positive Pathogens Unit, Paris, France.|Centre National de la Recherche Scientifique (CNRS) ERL3526, Paris, France.
authors.forename: Noémi
authors.initials: N
authors.lastname: Szili
authors.affiliation: Institut Pasteur, Biology of Gram-positive Pathogens Unit, Paris, France.|Centre National de la Recherche Scientifique (CNRS) ERL3526, Paris, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: du Merle
authors.affiliation: Institut Pasteur, Unité Ecologie et Evolution de la Résistance aux Antibiotiques, Paris, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Rosinski-Chupin
authors.affiliation: Institut Pasteur, Biology of Gram-positive Pathogens Unit, Paris, France.|Centre National de la Recherche Scientifique (CNRS) ERL3526, Paris, France.
authors.forename: Myriam
authors.initials: M
authors.lastname: Gominet
authors.affiliation: Équipe Barrières et Pathogènes, Institut Cochin, Inserm 1016, CNRS UMR, Paris France.|Assistance Publique-Hôpitaux de Paris, Hôpitaux Universitaires Paris Centre-Site Cochin, France.
authors.forename: Samuel
authors.initials: S
authors.lastname: Bellais
authors.affiliation: Équipe Barrières et Pathogènes, Institut Cochin, Inserm 1016, CNRS UMR, Paris France.|Assistance Publique-Hôpitaux de Paris, Hôpitaux Universitaires Paris Centre-Site Cochin, France.|CNR Streptocoques, Hôpitaux Universitaires Paris Centre, site Cochin, AP-HP.|DHU Risques et Grossesse, AP-HP, Paris, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Poyart
authors.affiliation: Institut Pasteur, Biology of Gram-positive Pathogens Unit, Paris, France.|Centre National de la Recherche Scientifique (CNRS) ERL3526, Paris, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Trieu-Cuot
authors.affiliation: Institut Pasteur, Biology of Gram-positive Pathogens Unit, Paris, France.|Centre National de la Recherche Scientifique (CNRS) ERL3526, Paris, France.
authors.forename: Shaynoor
authors.identifier: http://orcid.org/0000-0001-8323-3878
authors.initials: S
authors.lastname: Dramsi
mesh_terms: D018387:Codon, Initiator; D036781:Fimbriae Proteins / Q000235:genetics; D010861:Fimbriae, Bacterial / Q000378:metabolism; D017353:Gene Deletion; D005798:Genes, Bacterial; D009876:Operon; D013292:Streptococcus agalactiae / Q000235:genetics* / Q000472:pathogenicity; D014158:Transcription, Genetic; D014774:Virulence / Q000235:genetics*
chemical_list: D018387:Codon, Initiator; D036781:Fimbriae Proteins