14 research outputs found

    Histopathilogical analyses of mice infected with SCHU9 and Δ<i>pulB</i> mutant bacteria.

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    <p>Tissue sections obtained from mice infected with SCHU P9 and Δ<i>pulB</i> were examined by hematoxylin and eosin (HE) staining and immunohistochemistry (IHC) using anti-<i>Francisella tularensis</i> LPS monoclonal antibody. (A) Moderate focal necrosis and abscess were observed in lungs from mice infected with SCHU P9. Lungs from mice infected with Δ<i>pulB</i> showed milder pulmonary lesions compared to those from mice infected with SCHU P9. Vacuolar degeneration of hepatocytes, moderate focal necrosis and congestion were observed in livers of mice infected with SCHU P9. Livers from mice infected with Δ<i>pulB</i> showed milder focal necrosis. Marked focal necrosis associated with the accumulation of neutrophils was observed in the white pulp and red pulp of spleens from mice infected with SCHU P9 (3 dpi, original magnification x10). However, the accumulation of neutrophils was more prominent in the white pulp and around the central arteries or arterioles of spleens from mice infected with Δ<i>pulB</i> (right bottom square, original magnification x40). (B) Lung, liver and spleen from mice infected with SCHU P9 and Δ<i>pulB</i> were stained by immunohistochemical stain (IHC) with anti-<i>F</i>. <i>tularensis</i> LPS, N-Histofine Simple Stain MAX PO (M), and visualized by 3,3’-diaminobenzidine (DAB), followed by a hematoxylin counterstain (5 dpi, original magnification x10). LPS antigen positive foci, which are considered to be LPS-positive bacteria, were more prominent in SCHU P9-infected mice at 5 dpi compared to those in Δ<i>pulB</i>-infected mice.</p

    The comparisons of virulence of SCHU P9 and <i>ΔpulB</i> mutant bacteria in mice.

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    <p>Four C57BL/6J mice in each group (seven- to twelve-week-old females; SLC, Inc. Shizuoka, Japan) were intranasally inoculated with 10<sup>3</sup> CFU of SCHU P9 and Δ<i>pulB</i>, respectively. Survival rates (A) and body weights (B) of these mice were measured up to 6 dpi. Mice were sacrificed at the indicated dpi, and then the averages ± SD of bacterial CFU in lungs (C), livers (D), and spleens (E) were shown. ND, not detected.</p

    Pullulanase Is Necessary for the Efficient Intracellular Growth of <i>Francisella tularensis</i>

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    <div><p>Pullulanase, an enzyme that catalyzes the hydrolysis of polysaccharides, has been identified in a broad range of organisms, including bacteria, yeasts, fungi, and animals. The pullulanase (<i>pulB</i>; <i>FTT_0412c</i>) of <i>F</i>. <i>tularensis</i> subspecies <i>tularensis</i> Schu S4 is considered to be a homologue of the type I pullulanase (<i>pulA</i>) of the other <i>Francisella</i> subspecies. The significance of <i>Francisella</i> pullulanase has been obscure until now. In the present study, we characterized a recombinant PulB of <i>F</i>. <i>tularensis</i> SCHU P9, which was expressed as a his-tagged protein in <i>Escherichia coli</i>. The recombinant PulB was confirmed to be a type I pullulanase by its enzymatic activity <i>in vitro</i>. A <i>pulB</i> gene knockout mutant of <i>F</i>. <i>tularensis</i> SCHU P9 (Δ<i>pulB</i>) was constructed using the TargeTron Knockout system and plasmid pKEK1140 to clarify the function of PulB during the growth of <i>F</i>. <i>tularensis</i> in macrophages. The intracellular growth of the Δ<i>pulB</i> mutant in murine macrophage J774.1 cells was significantly reduced compared with that of the parental strain SCHU P9. Expression of PulB in Δ<i>pulB</i>, using an expression plasmid, resulted in the complementation of the reduced growth in macrophages, suggesting that PulB is necessary for the efficient growth of <i>F</i>. <i>tularensis</i> in macrophages. To assess the role of PulB in virulence, the knockout and parent bacterial strains were used to infect C57BL/6J mice. Histopathological analyses showed that tissues from Δ<i>pulB</i>-infected mice showed milder lesions compared to those from SCHU P9-infected mice. However, all mice infected with SCHU P9 and Δ<i>pulB</i> showed the similar levels of bacterial loads in their tissues. The results suggest that PulB plays a significant role in bacterial growth within murine macrophage but does not contribute to bacterial virulence <i>in vivo</i>.</p></div

    The intracellular growth of Δ<i>pulB</i> derived from virulent SCHU P9.

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    <p>(A) The insertion in Δ<i>pulB</i> derived from SCHU P9 was confirmed by PCR. Genomic DNA extracted from SCHU P9 and Δ<i>pulB</i> were subjected to PCR using gene specific sense/antisense (I), gene specific sense/EBS universal (II), and EBS universal/antisense (III) primer pairs. The amplicons and molecular weight marker were electrophoresed on a 0.7% agarose gel. (B) The schematic summary of Δ<i>pulB</i> generated in this study is shown. <i>ltr</i>B introns were inserted into the SCHU P9 <i>pulB</i> gene. The resultant mutant was designated Δ<i>pulB</i>. (C) J774.1 cells inoculated with virulent SCHU P9 (black bar), attenuated SCHU P5 (white bar), and Δ<i>pulB</i> (gray bar) at an MOI of 10, were incubated for 2 h and 26 h. Their intracellular CFUs were measured in triplicate. Mean ± SD of CFU are shown. Statistical significance was determined by using Student’s <i>t</i> test (***<i>P</i> < 0.001). (D) J774.1 cells were infected with Δ<i>pulB</i> complemented with a <i>pulB</i> gene expression plasmid (black bar) or a control plasmid (gray bar). The intracellular CFUs were measured in triplicate. Mean ± SD of CFU are shown. Statistical significance was determined by using Student’s <i>t</i> test (**<i>P</i> < 0.01).</p

    Characterization of the recombinant PulB of <i>F</i>. <i>tularensis</i> SCHU P9.

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    <p>(A) The plasmid pCold TF contains a <i>lac</i> operator, the cold shock protein A (<i>cspA</i>) 5' untranslated region (5' UTR), a translation enhancing element (TEE), a 6x His-tag sequence, the trigger factor sequence, protease cleavage sites, and a multiple cloning site (MCS) downstream of the <i>cspA</i> promoter. This plasmid, which is a cold shock expression vector, can express the target protein fused to a trigger factor under the control of the cold shock protein A (<i>cspA</i>) promoter and <i>lac</i> operator. In this study, the <i>pulB</i> gene fused with an N-terminal TEE sequence and a C-terminal 6x his-tag sequence was amplified from <i>F</i>. <i>tularensis</i> SCHU P9 DNA and then inserted into pCold TF plasmid lacking trigger factor, protease sites, and MCS using the In-Fusion HD Cloning Kit. (B) The expression and purification of the recombinant PulB. PulB expression was induced by IPTG in <i>E</i>. <i>coli</i> BL21(DE3) transformed with the pCold TF-pulB plasmid. Recombinant PulB was purified from the bacterial lysates using an AKTA start system equipped with a HisTrap HP column. Lane M, marker proteins (kDa); lane 1, <i>E</i>. <i>coli</i> BL21(DE3) lysates; lane 2, purified recombinant PulB. (C) The products of pullulan hydrolysis catalyzed by recombinant PulB are shown. Pullulan (P), maltotriose (G3), maltose (G2), and glucose (G1) were incubated in pH 6.2 phosphate buffer with (+) or without (–) the recombinant PulB at 37°C for 24 h. After this incubation, the samples were immediately heat denatured. The samples were subjected to TLC analysis using 2-propanol/acetic acid/water (4:1:1, vol/vol/vol) as the solvent system. (D and E) Effects of pH (D) and temperature (E) on recombinant PulB activity are shown. Recombinant PulB was incubated with 0.25% pullulan at 37°C for 12 h and then immediately heat denatured at 94°C for 15 min. The hydrolyzed products were measured in triplicate using the DNS method. After the background was subtracted from the data, the maximal relative activity was determined at pH 6.2 (D) and 37°C (E). Mean ± SD of relative activity are shown. The optimal pH was determined from a curve fitting (Gaussian) by GraphPad Prism software.</p

    Role of Pathogenicity Determinant Protein C (PdpC) in Determining the Virulence of the <i>Francisella tularensis</i> Subspecies <i>tularensis</i> SCHU

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    <div><p><i>Francisella tularensis</i> subspecies <i>tularensis</i>, the etiological agent of tularemia, is highly pathogenic to humans and animals. However, the SCHU strain of <i>F. tularensis</i> SCHU P0 maintained by passaging in artificial media has been found to be attenuated. To better understand the molecular mechanisms behind the pathogenicity of <i>F. tularensis</i> SCHU, we attempted to isolate virulent bacteria by serial passages in mice. SCHU P5 obtained after 5th passages in mice remained avirulent, while SCHU P9 obtained after 9th passages was completely virulent in mice. Moreover, SCHU P9 grew more efficiently in J774.1 murine macrophages compared with that in the less pathogenic SCHU P0 and P5. Comparison of the nucleotide sequences of the whole genomes of SCHU P0, P5, and P9 revealed only 1 nucleotide difference among P0, P5 and P9 in 1 of the 2 copies of pathogenicity determinant protein C (<i>pdpC</i>) gene. An adenine residue deletion was observed in the <i>pdpC1</i> gene of SCHU P0, P5, and P9 and in the <i>pdpC2</i> gene of SCHU P0, and P5, while P9 was characterized by the wild type <i>pdpC2</i> gene. Thus, SCHU P0 and P5 expressed only truncated forms of PdpC protein, while SCHU P9 expressed both wild type and truncated versions. To validate the pathogenicity of PdpC, both copies of the <i>pdpC</i> gene in SCHU P9 have been inactivated by Targetron mutagenesis. SCHU P9 mutants with inactivated <i>pdpC</i> gene showed low intracellular growth in J774.1 cells and did not induce severe disease in experimentally infected mice, while virulence of the mutants was restored by complementation with expression of the intact PdpC. These results demonstrate that PdpC is crucial in determining the virulence of <i>F. tularensis</i> SCHU.</p></div

    DNA sequencing analysis of the <i>pdpC</i> gene.

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    <p>(A) Mixtures of <i>pdpC1</i> and <i>pdpC2</i> DNAs amplified from the SCHU P0 (upper panel), P5 (middle panel), and P9 (lower panel) genomes were directly sequenced using Sanger’s method. The sequencing electropherograms of a region of <i>pdpC</i> from positions 2,031 to 2,056 are shown. (B) <i>pdpC1</i> (left panel) and <i>pdpC2</i> (right panel) were individually amplified by the long PCR method, and the amplicons were sequenced directly. The A tract found in the electropherograms is indicated as A8 or A9, as appropriate. (C) Deduced encoded amino acid sequences of PdpC2 from positions 661–720 obtained from SCHU P0, P5, and P9 were aligned. The asterisks and hyphens indicate the identical and untranslated amino acids, respectively. (D) Schematic representation of the structures of the <i>pdpC1</i> and <i>pdpC2</i> of <i>Francisella tularensis</i> SCHU S4, SCHU P0, SCHU P5, and SCHU P9. The translated and untranslated regions are indicated by black and white, respectively. The stop codons created by frameshift are indicated by arrowheads. (E) SCHU P0, P5, and P9 were grown in CDM and the lysates were subjected to western blot analyses using anti-PdpC polyclonal antibody <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0089075#pone.0089075-Chong1" target="_blank">[20]</a>. Intact PdpC was observed only in SCHU P9. Bands corresponding to the expected sizes of the intact or truncated PdpCs are indicated by gray and black arrowheads, respectively.</p
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