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2. Regulation of PI-2b Pilus Expression in Hypervirulent Streptococcus agalactiae ST-17 BM110

Author

Périchon, Bruno, Szili, Noémi, du Merle, Laurence, Rosinski-Chupin, Isabelle, Gominet, Myriam, Bellais, Samuel, Poyart, Claire, Trieu-Cuot, Patrick, Dramsi, Shaynoor, Bidault, Floran, Biologie des Bactéries pathogènes à Gram-positif, Institut Pasteur [Paris] (IP)-Centre National de la Recherche Scientifique (CNRS), Ecologie et Evolution de la Résistance aux Antibiotiques / Ecology and Evolution of Antibiotics Resistance (EERA), Institut Pasteur [Paris] (IP)-Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Université Paris Sud Orsay-Centre National de la Recherche Scientifique (CNRS), Institut Cochin (IC UM3 (UMR 8104 / U1016)), Université Paris Descartes - Paris 5 (UPD5)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), This work was supported by the DIM Malinf from the Conseil Régional d'Ile-de-France (Grant DIM130065) to CP and SD. NS was recipient of a doctoral fellowship from the DIM Malinf. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript., Université Paris-Sud - Paris 11 (UP11)-Institut Pasteur [Paris] (IP)-Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Centre National de la Recherche Scientifique (CNRS), Institut Pasteur [Paris]-Centre National de la Recherche Scientifique (CNRS), Institut Pasteur [Paris]-Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Université Paris Sud Orsay-Centre National de la Recherche Scientifique (CNRS), Institut Pasteur [Paris] - Centre National de la Recherche Scientifique (CNRS), Université Paris-Sud - Paris 11 (UP11) - Institut Pasteur [Paris] - Assistance publique - Hôpitaux de Paris (AP-HP) - Centre National de la Recherche Scientifique (CNRS), Institut Cochin (UM3 (UMR 8104 / U1016)), and Université Paris Descartes - Paris 5 (UPD5) - Institut National de la Santé et de la Recherche Médicale (INSERM) - Centre National de la Recherche Scientifique (CNRS)

Subjects
Transcription, Genetic, MESH: Codon, Initiator, [SDV]Life Sciences [q-bio], Codon, Initiator, lcsh:Medicine, MESH: Virulence, Biochemistry, Nucleic Acids, Lactococcus, lcsh:Science, Pathology and laboratory medicine, Virulence, Genomics, Medical microbiology, [SDV] Life Sciences [q-bio], Group B streptococci, Fimbriae Proteins, Pathogens, Cellular Structures and Organelles, MESH: Genes, Bacterial, Lactococcus Lactis, Research Article, Pathogen Motility, MESH: Operon, Virulence Factors, DNA transcription, Microbiology, Streptococcus agalactiae, MESH: Fimbriae, Bacterial, Operon, Genetics, Operons, Gene Prediction, Medicine and health sciences, Bacteria, MESH: Transcription, Genetic, lcsh:R, Organisms, Biology and Life Sciences, Streptococcus, Computational Biology, Cell Biology, DNA, Genome Analysis, MESH: Fimbriae Proteins, MESH: Streptococcus agalactiae, Microbial pathogens, Pili and Fimbriae, Genetic Loci, Genes, Bacterial, MESH: Gene Deletion, Fimbriae, Bacterial, Bacterial pathogens, lcsh:Q, Gene expression, Gene Deletion
Abstract

International audience; 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 gfpas 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 gfpas 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 BM110AcovR 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.

Published
2017

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