11 research outputs found

    Isolation, phenotypic analyses and sequencing of Pil1+ variants.

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    <p>(A) Detection of Pil1+ variants by colony blot using anti-PilB pAb. Isolated bacteria on a TH agar plate (left) and corresponding replicate hybridized with anti-PilB pAb (right). Arrowheads indicate the few variants displaying a Pil1+ phenotype. (B) Serial analysis of Pil1 expression in WT and Pil1+<sub>var</sub> populations. Individual colonies of WT UCN34 strain isolated on TH agar plates were grown in 96 well plates, transferred to a Nylon membrane, and probed with anti-PilB. Analysis of one Pil1+ variant revealed that it subsequently generates a majority of Pil1+ colonies (90–95%) and a minority of Pil1<sub>low</sub> cells (5–10%) thus displaying phenotypic pilus heterogeneity as the WT UCN34. (C–F) Phenotypic comparison of WT UCN34 and Pil1+<sub>var23</sub> variant. Scanning immunogold electron microscopy (C) and flow cytometry (D) analyses of bacteria labeled with anti-PilB pAb. Western blot analysis (E) of cell wall protein extracts revealed with anti-PilB pAb. Quantitative RT-PCR analysis (F) of RNAs extracted from exponentially growing <i>S. gallolyticus</i> cells. The expression levels were normalized using 16S rRNA as an internal standard and are indicated as the n-fold change with respect to the WT strain 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. The location in the <i>pil1</i> operon of the four primer pairs used is indicated at the bottom. (G) Sequence and flow cytometry analyses of WT UCN34 and Pil1+<sub>var</sub> strains. Frameshift addition/deletion GCAGA repeats in the leader peptide encoding gene did not modify the Pil1 expression profile of UCN34 WT whereas out-of-frame addition were always associated with a Pil1+ phenotype.</p

    Heterogeneous expression of Pil1 depends on its 5′ upstream region.

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    <p>(A–D) Flow cytometry profiles of the WT UCN34 strain, the isogenic Δ<i>pil1</i> mutant, and the Δ<i>pil1</i> complemented with pTCV<i>erm</i>-P<i>tet</i>-<i>pil1</i> or pTCV<i>erm</i>-P<i>pil1</i>-<i>pil1</i>. (A) The WT strain displays two cell subpopulations, a majority of Pil1<sub>low</sub> (66%) and a minority of Pil1<sub>high</sub> (27%). (B) The Δ<i>pil1</i> mutant that does not express the Pil1 pilus. (C) The Δ<i>pil1</i> mutant complemented with the plasmid pTCV<i>erm</i>-P<i>tet</i>-<i>pil1</i>, P<i>tet</i> being a constitutive promoter, displays a single population of highly piliated cells. (D) The Δ<i>pil1</i> mutant complemented with the plasmid pTCV<i>erm</i>-P<i>pil1</i>-<i>pil1</i>, P<i>pil1</i> being the entire <i>gallo2180-pilA</i> intergenic region, displays two subpopulations. (C–D) Immunofluorescence staining with anti-PilB pAb (green) confirms that only the P<i>pil1</i> promoter and downstream sequences restored the heterogeneous expression of the Pil1 pilus (Pil1<sub>low</sub>, 76%; Pil1<sub>high</sub>, 16%). Bacteria were stained with DAPI (blue).</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

    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

    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

    Different steps of bacterial spread during bubonic plague.

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    <p>The bioluminescent signal was visible first at the injection site (A). It then reached the inguinal lymph node (B), the axillary lymph node (C), the liver (D, dorsal position) and the spleen (D, ventral position), and finally the entire body (E). Each picture is an example of an animal displaying a signal characteristic of each step. The color scale on the right represents the settings used to monitor light emission in all mice throughout the observation period.</p

    Time of appearance of a bioluminescent signal in the various organs of infected mice.

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    <p>Each circle corresponds to an individual animal. Horizontal bars represent the mean and vertical bars the standard error of the mean of the data collected from 24 mice. LN: lymph node.</p

    Linking a bioluminescence signal to the colonization of a specific organ.

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    <p>(A) Example of the light emitted by a live animal. (B) Light emitted by the organs of the same animal. Arrows point at: (1) axillary lymph nodes, (2) liver (one lobe still in place and the remaining of the organ removed from its anatomical site), (3) injection site (split in two parts during dissection), (4) inguinal lymph nodes, and (5) spleen (removed from its anatomical site and visualized in live animals mostly in ventral position). On the dissection picture, the gut has been removed and placed next to the right hind leg, while the peritoneum including a portion of the infection site is located next to the left hind leg. Color bars on the right of each picture show the intensity of bioluminescence light coded in the picture from indigo to red.</p
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