Heme rescues a two-component system Leptospira biflexa mutant

<p>Abstract</p> <p>Background</p> <p>Heme is typically a major iron source for bacteria, but little is known about how bacteria of the <it>Leptospira </it>genus, composed of both saprophytic and pathogenic species, access heme.</p> <p>Results</p> <p>In this study, we analysed a two-component system of the saprophyte <it>Leptospira biflexa</it>. <it>In vitro </it>phosphorylation and site-directed mutagenesis assays showed that Hklep is a histidine kinase which, after autophosphorylation of a conserved histidine, transfers the phosphate to an essential aspartate of the response regulator Rrlep. Hklep/Rrlep two-component system mutants were generated in <it>L. biflexa</it>. The mutants could only grow in medium supplemented with hemin or δ-aminolevulinic acid (ALA). In the pathogen <it>L. interrogans</it>, the <it>hklep </it>and <it>rrlep </it>orthologous genes are located between <it>hemE </it>and <it>hemL </it>genes, which encode proteins involved in heme biosynthesis. The <it>L. biflexa hklep </it>mutant could be complemented with a replicative plasmid harbouring the <it>L. interrogans </it>orthologous gene, suggesting that these two-component systems are functionally similar. By real-time quantitative reverse transcription-PCR, we also observed that this two-component system might influence the expression of heme biosynthetic genes.</p> <p>Conclusion</p> <p>These findings demonstrate that the Hklep/Rrlep regulatory system is critical for the <it>in vitro </it>growth of <it>L. biflexa</it>, and suggest that this two-component system is involved in a complex mechanism that regulates the heme biosynthetic pathway.</p

Une subjectivité qui se dérobe : l'effacement des marques dans «Strandhill, the Sea», de John McGahern

The representation of subjectivity in “Strandhill, the Sea”, by John McGahern, is highly paradoxical, for subjective point of view seems scarcely to be marked and yet is ever present. Our study of the tenuous traces of point of view shows how the centre of consciousness — that of the child as “recorder” of the adults’ world — is built up through ellipsis, parataxis, indétermination and “fuzziness”. This elusive subject can assert himself only by taking refuge in the “world of imagination”, which enables him both to bring together the strands of the story and to escape from the mediocrity of the adults’ world.La représentation de la subjectivité dans “Strandhill, the Sea” de John McGahem, est de nature paradoxale, tant sont ténus les indices d’un point de vue subjectif, pourtant omniprésent. Nous examinons les marques éparses de ce point de vue et nous montrons comment, par le biais de l’ellipse, de la parataxe, de l’indétermination, du «brouillage », se construit en creux le centre de conscience — l’enfant comme «chambre d’enregistrement» du monde des adultes. Ce sujet qui se dérobe ne peut s’affirmer que par l’évasion dans un «monde de l’imagination» qui lui permet à la fois de nouer les fils (strands) de l’histoire et d’échapper à la médiocrité du monde des adultes.Louvel Liliane, Chuquet H. Une subjectivité qui se dérobe : l'effacement des marques dans «Strandhill, the Sea», de John McGahern. In: Cahiers Charles V, n°33, mars 2003. Littérature / linguistique. Lectures croisées. pp. 99-120

Les systèmes d'acquisition du fer chez les leptospires

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Isolation and Characterization of FecA- and FeoB-Mediated Iron Acquisition Systems of the Spirochete Leptospira biflexa by Random Insertional Mutagenesis

The specific mechanisms by which Leptospira spp. acquire iron from their ecological niches are unknown. A major factor contributing to our ignorance of spirochetal biology is the lack of methods for genetic analysis of these organisms. In this study, we have developed a system for random transposon mutagenesis of Leptospira biflexa using a mariner transposon, Himar1. To demonstrate the validity of Himar1 in vivo transposon mutagenesis in L. biflexa, a screen of mutants for clones impaired in amino acid biosynthesis was first performed, enabling the identification of tryptophan and glutamate auxotrophs. To investigate iron transporters, 2,000 L. biflexa transposon mutants were screened onto media with and without hemin, thus allowing the identification of five hemin-requiring mutants, and the putative genes responsible for this phenotype were identified. Three mutants had distinct insertions in a gene encoding a protein which shares homology with the TonB-dependent receptor FecA, involved in ferric citrate transport. We also identified two mutants with a Himar1 insertion into a feoB-like gene, the product of which is required for ferrous iron uptake in many bacterial organisms. Interestingly, the growth inhibition exhibited by the fecA and feoB mutants was relieved by deferoxamine, suggesting the presence of a ferric hydroxamate transporter. These results confirm the importance of iron for the growth of Leptospira and its ability to use multiple iron sources

Random Insertional Mutagenesis of Leptospira interrogans, the Agent of Leptospirosis, Using a mariner Transposon

The recent availability of the complete genome sequences of Leptospira interrogans, the agent of leptospirosis, has allowed the identification of several putative virulence factors. However, to our knowledge, attempts to carry out gene transfer in pathogenic Leptospira spp. have failed so far. In this study, we show that the Himar1 mariner transposon permits random mutagenesis in the pathogen L. interrogans. We have identified genes that have been interrupted by Himar1 insertion in 35 L. interrogans mutants. This approach of transposon mutagenesis will be useful for understanding the spirochetal physiology and the pathogenic mechanisms of Leptospira, which remain largely unknown

Low P-T evolution of the continental crust exhumed during the Woodlark basin seafloor spreading system

Proceedings O.D.P., Sci. Results, leg 180, v. 180SR-178 [624], 2002International audienc

The use of a multicellular in vitro model to investigate uptake and migration of bacterial extracellular vesicles derived from the human gut commensal Bacteroides thetaiotaomicron

Abstract Bacterial extracellular vesicles (BEVs) are increasingly seen as key signalling mediators between the gut microbiota and the host. Recent studies have provided evidence of BEVs ability to transmigrate across cellular barriers to elicit responses in other tissues, such as the central nervous system (CNS). Here we use a combination of single‐, two‐ and three‐cell culture systems to demonstrate the transmigration of Bacteroides thetaiotaomicron derived BEVs (Bt‐BEVs) across gut epithelium and blood brain barrier (BBB) endothelium, and their subsequent acquisition and downstream effects in neuronal cells. Bt‐BEVs were shown to traffic to the CNS in vivo after intravenous administration to mice, and in multi‐cell in vitro culture systems to transmigrate across gut epithelial and BBB endothelial cell barriers, where they were acquired by both microglia and immature neuronal cells. No significant activation/inflammatory effects were induced in non‐differentiated neurons, in contrast to that observed in microglia cells, although this was notably less than that induced by lipopolysaccharide (LPS). Overall, our findings provide evidence for transmigration of Bt‐BEVs across gut‐epithelial and BBB endothelial cell barriers in vivo and in vitro, and their downstream responses in neural cells. This study sheds light onto how commensal bacteria‐derived BEV transport across the gut‐brain axis and can be exploited for the development of targeted drug delivery

Structural and Functional Characterization of an Orphan ATP-Binding Cassette ATPase Involved in Manganese Utilization and Tolerance in Leptospira spp

International audienceABSTRACT Pathogenic Leptospira species are the etiological agents of the widespread zoonotic disease leptospirosis. Most organisms, including Leptospira , require divalent cations for proper growth, but because of their high reactivity, these metals are toxic at high concentrations. Therefore, bacteria have acquired strategies to maintain metal homeostasis, such as metal import and efflux. By screening Leptospira biflexa transposon mutants for their ability to use Mn 2+ , we have identified a gene encoding a putative orphan ATP-binding cassette (ABC) ATPase of unknown function. Inactivation of this gene in both L. biflexa and L. interrogans strains led to mutants unable to grow in medium in which iron was replaced by Mn 2+ , suggesting an involvement of this ABC ATPase in divalent cation uptake. A mutation in this ATPase-coding gene increased susceptibility to Mn 2+ toxicity. Recombinant ABC ATPase of the pathogen L. interrogans exhibited Mg 2+ -dependent ATPase activity involving a P-loop motif. The structure of this ATPase was solved from a crystal containing two monomers in the asymmetric unit. Each monomer adopted a canonical two-subdomain organization of the ABC ATPase fold with an α/β subdomain containing the Walker motifs and an α subdomain containing the ABC signature motif (LSSGE). The two monomers were arranged in a head-to-tail orientation, forming a V-shaped particle with all the conserved ABC motifs at the dimer interface, similar to functional ABC ATPases. These results provide the first structural and functional characterization of a leptospiral ABC ATPase

L'immobilité vive

Ce numéro propose d’interroger une fois de plus le dialogue entre le texte et l’image en examinant tout particulièrement ces éclats de temps que nous offrent les « arts sœurs », ces moments où s’allient l’immobilité et le mouvement – ou encore ces moments tout court, puisque le « momentum », mouvement ou impulsion, mais aussi influence, poids, importance, porte déjà en lui le temps et son suspens. Si en peinture c’est la nature morte (Still Life, Stilleven, Stillleben) qui, par excellence, met à l’œuvre la tension entre le temps en mouvement et l'inscription dans l’espace, le moment se décline de bien d’autres façons encore dans les arts visuels : moments de surprise liés à une rencontre ou une révélation, moments de terreur et d’effroi, moments de fascination, d’extase ou de ravissement, ou encore moments de grâce. L’image semble ainsi dotée du pouvoir d’accueillir le temps en défiant la fixité qui est la sienne, ou, à l’inverse, exacerbe son pouvoir de figer les corps pour manifester un point d’intensité ou d’arrêt qui porte la trace d’un événement. Qu’elle s’anime ou se pétrifie, qu’elle nous mette face à un bougé, à un tremblé, ou qu’elle porte à son paroxysme la stase, l’image déploie le spectre de son pouvoir à exprimer une « immobilité vive », selon l’expression de Roland Barthes (La Chambre claire). Le texte a lui aussi mille et une façons de dire la tension entre le mouvement et la stase. Ce numéro propose d'examiner la manière dont les mots mettent l’image, réelle ou virtuelle, littérale ou figurée, au service du moment, ou encore la façon dont on peut dire que le texte « fait image » pour citer Jean-Luc Nancy (Au fond des images). En « faisant image », le texte peut manifester un suspens, un effacement ou un effondrement du sens à travers lequel les registres visuel et vocal se brouillent, comme le souligne Pierre Fédida dans « Le souffle indistinct de l’image ». Avec cette conception de l'image comme « arrêt sur le langage, instant d’abîme du mot » (Fédida), ce sont aussi les questions du déplacement métaphorique et du figural, et de son écart éventuel avec l’ordre du visuel, qui sont abordées. This issue proposes to pursue its scrutiny of the dialogue between text and image, by looking into these shards of time that the « sister arts » offer us, these moments in which stasis and movement combine, since the Latin « momentum » means both motion / impulse and weight / importance. With the still life (Stilleven, Stillleben), painting offers a perfect example of the synthesis between the passing of time and its inscription in space. But the moment finds many other forms of expression in the visual arts: we can think of the moments of surprise produced by an encounter or a revelation, moments of terror and fright, moments of fascination and rapture, or moments of grace. The image seems to be able to counter its fixity and accommodate time, or conversely exhibits its power to freeze things in order to mark a point of intensity which bears the trace of an event. Whether it emphasizes motion or petrification, vacillation or stasis, the image deploys the full spectrum of its power to convey « intense immobility », « une immobilité vive » in the words of Roland Barthes (Camera Lucida). Texts too have many ways of expressing the tension between movement and stasis. This issue looks at the way in which texts use images, whether real or virtual, literal or figurative, to suggest moments of time, or even claim the power of the image, in the process which Jean-Luc Nancy calls « faire image » ‒ by which he means « to highlight, to stress, to underline, to make present ». « Faire image » can describe the suspension, obliteration or collapse of meaning, a point where the visual and the aural dimensions fuse, as Pierre Fédida writes in « The Indistinct Breath of the Image ». With this definition of the image as « a freezing of language, the moment of failure of the word » (Fédida), one should also be able to look into the questions of metaphorical displacement and of the figural, in its connection with, or independence from, the visual field