32 research outputs found

    Uncoupling transcription and translation in the <i>pil1</i> operon.

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    <p>Quantitative RT-PCR were performed on RNAs extracted from UCN34 WT and Pil1+<sub>var23</sub> variant grown without or with chloramphenicol (8 µg/mL) to induce ribosome stalling in leader peptide mRNA. The expression levels were normalized using 16S rRNA as an internal standard and are indicated as the n-fold change with respect to untreated WT strain UCN34, expressed as means and standard deviations of at least three separate experiments. The gene <i>tanA</i> was used as a reference gene whose transcription is not affected by addition of chloramphenicol. Asterisks represent P values (*<i>P</i><0.05) evaluated using a Student <i>t</i> test. The location in the <i>pil1</i> operon of the four primer pairs used is indicated at the bottom.</p

    Model of pilus regulation by an attenuation-like mechanism.

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    <p>(A) <i>S. gallolyticus</i> UCN34 WT displays a heterogeneous <i>pil1</i> expression and consists of two main subpopulations, a majority of low piliated cells (Pil1<sub>low</sub>, 70%) and a minority of hyper piliated cells (Pil1<sub>high</sub>, 30%). The Pil1<sub>low</sub> cells, characterized by a basal expression of <i>pil1</i>, possess a regulatory leader peptide-encoding gene with 22 GCAGA repeats that ends 39 bp upstream the hairpin transcription terminator. In-frame addition/deletion of GCAGA did not modify the distance between the leader peptide stop codon and the terminator. In this case, most transcripts initiated at P<i>pil1</i> promoter end at this premature terminator and the observed low expression of <i>pil1</i> probably occurs by readthrough transcription. The Pil1<sub>high</sub> cells, characterized by a strong expression of <i>pil1</i>, displayed out-of-frame addition/deletion of repeats resulting in the synthesis of longer regulatory peptides whose stop codon are located within or dowstream of the hairpin terminator. Translation of these long regulatory leader peptides enhances <i>pil1</i> genes transcription by preventing the formation of the transcription terminator. (B) Flow cytometry analysis of UCN34 WT and isogenic mutant derivatives (Δ<i>term</i>, ATG*, and 3 STOPs) labeled with anti-PilB pAb. The WT and mutant profiles are depicted by gray area and black lines, respectively. Note that, as expected, the UCN34 and “back to the WT” profiles, depicted by dotted lines, are almost entirely superimposable. (C) Immunolabeling screening of the Pil1+<sub>var23</sub> and Δ<i>term</i> strains with anti-PilB pAb. As opposed to the Pil1+<sub>var23</sub> variant, the Δ<i>term</i> mutant is homogeneous and only generates Pil1+ colonies. This is the consequence of the deletion of the transcription terminator that blocks this strain in the Pil1<sub>high</sub> configuration. (D) Quantitative RT-PCR were performed on RNAs extracted from WT UCN34 and mutant derivatives using pilB primers. The expression levels were normalized using 16S rRNA as an internal standard and are indicated as the n-fold change with respect to WT UCN34, expressed as means and standard deviations of at least three independent experiments with four technical replicates. Asterisks represent P values (** <i>P</i><0.05) evaluated using a Student <i>t</i> test.</p

    Uptake of <i>S. gallolyticus</i> UCN34 WT, Δ<i>pil1</i>, and Δ<i>term</i> (Pil1+<sub>locked</sub>) strains by human THP-1 macrophages.

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    <p>(A) Indirect immunofluorescence microscopy showing phagocytosis of Δ<i>pil1</i> or Δ<i>term</i> (Pil1+<sub>locked</sub>) mutants by THP-1 macrophages in the presence of anti-Pil1 antibody (opsonophagocytic assay). Actin is depicted in grey-purple, Hoeschst 33342 in blue, intracellular bacteria in green, and extracellular bacteria in yellow (green+red). (B) Percentage of phagocytosis by THP-1 human macrophages after 1 h of infection with WT, Δ<i>pil1</i>, and Δ<i>term</i> (Pil1+<sub>locked</sub>) strains, with or without an anti-Pil1 antibody. Values are representative of at least 4 independant experiments. (C) Flow-cytometry analysis of Pil1 expression performed on the UCN34 WT from the inoculum (grey) or from intracellular UCN34 bacteria recovered from THP-1 macrophages in an opsonophagocytic assay with an anti-PilB pAb (black lines are 3 replicates from one experiment).</p

    Expression in GBS of Bsp recombinant proteins with structurally unrelated signal peptides.

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    <p>(A) <i>Bam</i>HI-<i>Not</i>I PCR fragments carrying the ribosome binding site (RBS) and the signal peptides (SP) of 5 SecA-dependent substrates (Bsp, Alp2, Gbs0791, PilB, and CspA) were fused in frame with a <i>Not</i>I-<i>Pst</i>I PCR fragment coding the Bsp protein devoid of its signal peptide (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065832#pone.0065832.s004" target="_blank">Table S1</a>). The resulting <i>Bam</i>HI-<i>Pst</i>I fragments were cloned downstream the constitutive P<i>tetM</i> promoter from the low-copy-number pTCV<i>-erm</i>. The SP and Bsp sequences are indicated in upper-bold italic characters and upper-bold characters, respectively. The boxed RP motif in all proteins corresponded to the translation of the two internal codons of the <i>Not</i>I restriction site (CGGCCG). All but one SP were predicted with SignalP 4.1 (<a href="http://www.cbs.dtu.dk/services/SignalP/" target="_blank">www.cbs.dtu.dk/services/SignalP/</a>) whereas the remaining (Alp2) was predicted with PrediSi (<a href="http://www.predisi.de" target="_blank">www.predisi.de</a>). The AA residues in the SP thought to direct localized secretion at the bacterial surface are indicated in red characters. Arrowheads indicate the predicted site of cleavage of the various SP. (B) Analysis of surface display of Bsp recombinant proteins in a Δ<i>bsp</i> mutant strain by immunoblotting. Whole bacterial cells harvested in exponential (OD<sub>600</sub> 0.3) or stationary (OD<sub>600</sub> 1.2) phases were washed, resuspended in phosphate buffer saline to similar density and spotted on nitrocellulose. Membranes were hybridized with specific anti-Bsp antibodies or with anti-GBS pAb (loading control). (C) Western blotting analysis of culture supernatants. Proteins were separated on 4–12% gradient Tris-acetate Criterion XT SDS-PAGE gel, then transferred onto a nitrocellulose membrane, and detected by immunoblotting with specific anti-Bsp and anti-CAMP antibodies. In (B) and (C), the Δ<i>bsp</i> mutant strain harboring pTCV-<i>erm</i> (negative control) or pTCV-<i>erm</i> directing synthesis of recombinant Bsp proteins associated with Alp2, Gbs0791, PilB, and CspA signal peptides were used.</p

    Heterogeneous expression of Pil1 pilus at the <i>Streptococcus gallolyticus</i> UCN34 surface.

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    <p>(A–B) Scanning immunogold electron microscopy and immunofluorescence of <i>S. gallolyticus</i> UCN34 strain and <i>L. lactis</i> NZ9000 pOri23Ω<i>pil1</i> strain expressing <i>pil1</i>. Pili were revealed with an anti-PilB polyclonal antibody (pAb) coupled to 10 nm gold beads (A) or the DyLight 488 rabbit secondary antibody (B). (C) Flow cytometry analysis of <i>S. gallolyticus</i> UCN34 cell populations labeled with anti-PilB pAb and the DyLight 488 rabbit secondary antibody. Results are represented as dot plots (left) or as a graph (right). The two groups (left) or peaks (right) in black correspond to the heterogeneous UCN34 WT strain constituted of a weakly piliated subpopulation (Pil1<sub>low</sub> cells) and of a hyper piliated subpopulation (Pil1<sub>high</sub> cells) representing 67% and 28% of the total population respectively. The negative population in gray corresponds to the isogenic Δ<i>pil1</i> mutant (Pil1<sub>neg</sub>).</p

    The <i>pil1</i> locus of <i>S. gallolyticus</i> strain UCN34.

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    <p>(A) Schematic representation of the <i>pil1</i> operon constituted of three genes: <i>pilA</i>, encoding the pilus adhesin, <i>pilB</i> encoding the major pilin and <i>srtC</i>, encoding the sortase required for pilus polymerization. Relevant domains are: COL, collagen-binding domain (Pfam 05737); and LPXTG, cell wall-anchoring domain. The P<i>pil1</i> promoter, the premature terminator upstream <i>pilA</i> and the putative terminator (hairpin structures) downstream <i>srtC</i> delineating the <i>pil1</i> operon are indicated. (B) Schematic representation of the intergenic region <i>gallo2180-pilA</i> with the 22 GCAGA repeats striped in gray and white and the stem-loop structure. (C) Determination of transcription start sites (TSS) of the <i>pil1</i> operon by primer extension analysis. The band indicated as “+1” corresponds to the location upstream the leader peptide gene is the likely TSS of the <i>pil1</i> operon; the band marked as “*” is located within one inverted repeat of the stem-loop structure and is likely generated by a pause of the RNA polymerase during elongation. (D) Nucleotide sequence of the intergenic region <i>gallo2180-pilA</i> showing the -35 and -10 promoter boxes and the +1 site, the leader peptide coding sequence with the 22 GCAGA repeats, the downstream stem-loop structure, the <i>pilA</i> initiator codon and the predicted ribosome binding site (RBS). (E) The predicted secondary structure of the stem-loop transcription terminator identified upstream ATG<i><sub>pilA</sub></i> (according to The mfold WebServer, <a href="http://mfold.rna.albany.edu/?q=mfold/RNA-Folding-Form" target="_blank">http://mfold.rna.albany.edu/?q=mfold/RNA-Folding-Form</a>).</p