Les endocardites dues aux germes du groupe HACEK. A propos d'un cas d'endocardite native a Kingella kingae. [Endocarditis due to HACEK bacteria. A case report of endocarditis due to Kingella kingae]

Endocarditis is a common disease in hospital practice. Identification of the microorganism responsible for the valvular damage is essential to establish the prognosis and to determine the optimal antibiotic treatment. In some cases of endocarditis the diagnosis is laborious, especially when the responsible microorganism is difficult to detect using standard culture techniques. Here we report a case of native aortic valve endocarditis due to Kingella kingae, a Gram negative organism of the HACEK group. In addition we review 6 other cases of endocarditis caused by organism belonging to this group, treated in our hospital between 1983 and 1999. Epidemiological studies show that less than 5% of all cases of endocarditis are caused by organisms of the HACEK group. The diagnosis is often delayed because their slow growth on a standard culture medium. We describe clinical and microbiological characteristics of this group of endocarditis.

Endosymbiotic bacteria associated with nematodes, ticks and amoebae.

Endosymbiosis is a mutualistic, parasitic or commensal symbiosis in which one symbiont is living within the body of another organism. Such symbiotic relationship with free-living amoebae and arthropods has been reported with a large biodiversity of microorganisms, encompassing various bacterial clades and to a lesser extent some fungi and viruses. By contrast, current knowledge on symbionts of nematodes is still mainly restricted to Wolbachia and its interaction with filarial worms that lead to increased pathogenicity of the infected nematode. In this review article, we aim to highlight the main characteristics of symbionts in term of their ecology, host cell interactions, parasitism and co-evolution, in order to stimulate future research in a field that remains largely unexplored despite the availability of modern tools.

Regulation of phosphate starvation responses in plants: signaling players and cross-talks.

Phosphate (Pi) availability is a major factor limiting growth, development, and productivity of plants. In both ecological and agricultural contexts, plants often grow in soils with low soluble phosphate content. Plants respond to this situation by a series of developmental and metabolic adaptations that are aimed at increasing the acquisition of this vital nutrient from the soil, as well as to sustain plant growth and survival. The development of a comprehensive understanding of how plants sense phosphate deficiency and coordinate the responses via signaling pathways has become of major interest, and a number of signaling players and networks have begun to surface for the regulation of the phosphate-deficiency response. In practice, application of such knowledge to improve plant Pi nutrition is hindered by complex cross-talks, which are emerging in the face of new data, such as the coordination of the phosphate-deficiency signaling networks with those involved with hormones, photo-assimilates (sugar), as well as with the homeostasis of other ions, such as iron. In this review, we focus on these cross-talks and on recent progress in discovering new signaling players involved in the Pi-starvation responses, such as proteins having SPX domains.

Impact of biocontrol strain Pseudomonas fluorescens CHA0 on rhizosphere bacteria isolated from barley (Hordeum vulgare L.) with special reference to Cytophaga-like bacteria.

AIMS: To assess the impact of the biocontrol strain Pseudomonas fluorescens CHA0 on a collection of barley rhizosphere bacteria using an agar plate inhibition assay and a plant microcosm, focusing on a CHA0-sensitive member of the Cytophaga-like bacteria (CLB). METHODS AND RESULTS: The effect of strain CHA0 on a collection of barley rhizosphere bacteria, in particular CLB and fluorescent pseudomonads sampled during a growth season, was assessed by a growth inhibition assay. On average, 85% of the bacteria were sensitive in the May sample, while the effect was reduced to around 68% in the July and August samples. In the May sample, around 95% of the CLB and around 45% of the fluorescent pseudomonads were sensitive to strain CHA0. The proportion of CHA0-sensitive CLB and fluorescent pseudomonad isolates decreased during the plant growth season, i.e. in the July and August samples. A particularly sensitive CLB isolate, CLB23, was selected, exposed to strain CHA0 (wild type) and its genetically modified derivatives in the rhizosphere of barley grown in gnotobiotic soil microcosms. Two dry-stress periods were imposed during the experiment. Derivatives of strain CHA0 included antibiotic or exopolysaccharide (EPS) overproducing strains and a dry-stress-sensitive mutant. Despite their inhibitory activity against CLB23 in vitro, neither wild-type strain CHA0, nor any of its derivatives, had a major effect on culturable and total cell numbers of CLB23 during the 23-day microcosm experiment. Populations of all inoculants declined during the two dry-stress periods, with soil water contents below 5% and plants reaching the wilting point, but they recovered after re-wetting the soil. Survival of the dry-stress-sensitive mutant of CHA0 was most affected by the dry periods; however, this did not result in an increased population density of CLB23. CONCLUSIONS: CLB comprise a large fraction of barley rhizosphere bacteria that are sensitive to the biocontrol pseudomonad CHA0 in vitro. However, in plant microcosm experiments with varying soil humidity conditions, CHA0 or its derivatives had no major impact on the survival of the highly sensitive CLB strain, CLB23, during two dry-stress periods and a re-wetting period; all co-existed well in the rhizosphere of barley plants. SIGNIFICANCE AND IMPACT OF THE STUDY: Results indicate a lack of interaction between the biocontrol pseudomonad CHA0 and a sensitive CLB when the complexity increases from agar plate assays to plant microcosm experiments. This suggests the occurrence of low levels of antibiotic production and/or that the two bacterial genera occupy different niches in the rhizosphere.

Identification of active oxalotrophic bacteria by Bromodeoxyuridine DNA labeling in a microcosm soil experiments

The oxalate-carbonate pathway (OCP) leads to a potential carbon sink in terrestrial environments. This process is linked to the activity of oxalotrophic bacteria. Although isolation and molecular characterizations are used to study oxalotrophic bacteria, these approaches do not give information on the active oxalotrophs present in soil undergoing the OCP. The aim of this study was to assess the diversity of active oxalotrophic bacteria in soil microcosms using the Bromodeoxyuridine (BrdU) DNA labeling technique. Soil was collected near an oxalogenic tree (Milicia excelsa). Different concentrations of calcium oxalate (0.5%, 1%, and 4% w/w) were added to the soil microcosms and compared with an untreated control. After 12days of incubation, a maximal pH of 7.7 was measured for microcosms with oxalate (initial pH 6.4). At this time point, a DGGE profile of the frc gene was performed from BrdU-labeled soil DNA and unlabeled soil DNA. Actinobacteria (Streptomyces- and Kribbella-like sequences), Gammaproteobacteria and Betaproteobacteria were found as the main active oxalotrophic bacterial groups. This study highlights the relevance of Actinobacteria as members of the active bacterial community and the identification of novel uncultured oxalotrophic groups (i.e. Kribbella) active in soils.

Pyrroloquinoline quinone biosynthesis gene pqqC, a novel molecular marker for studying the phylogeny and diversity of phosphate-solubilizing pseudomonads.

Many root-colonizing pseudomonads are able to promote plant growth by increasing phosphate availability in soil through solubilization of poorly soluble rock phosphates. The major mechanism of phosphate solubilization by pseudomonads is the secretion of gluconic acid, which requires the enzyme glucose dehydrogenase and its cofactor pyrroloquinoline quinone (PQQ). The main aim of this study was to evaluate whether a PQQ biosynthetic gene is suitable to study the phylogeny of phosphate-solubilizing pseudomonads. To this end, two new primers, which specifically amplify the pqqC gene of the Pseudomonas genus, were designed. pqqC fragments were amplified and sequenced from a Pseudomonas strain collection and from a natural wheat rhizosphere population using cultivation-dependent and cultivation-independent approaches. Phylogenetic trees based on pqqC sequences were compared to trees obtained with the two concatenated housekeeping genes rpoD and gyrB. For both pqqC and rpoD-gyrB, similar main phylogenetic clusters were found. However, in the pqqC but not in the rpoD-gyrB tree, the group of fluorescent pseudomonads producing the antifungal compounds 2,4-diacetylphloroglucinol and pyoluteorin was located outside the Pseudomonas fluorescens group. pqqC sequences from isolated pseudomonads were differently distributed among the identified phylogenetic groups than pqqC sequences derived from the cultivation-independent approach. Comparing pqqC phylogeny and phosphate solubilization activity, we identified one phylogenetic group with high solubilization activity. In summary, we demonstrate that the gene pqqC is a novel molecular marker that can be used complementary to housekeeping genes for studying the diversity and evolution of plant-beneficial pseudomonads.

Characterization of the PHO1 gene family and the responses to phosphate deficiency of Physcomitrella patens.

PHO1 was previously identified in Arabidopsis (Arabidopsis thaliana) as a protein involved in loading inorganic phosphate (Pi) into the xylem of roots and its expression was associated with the vascular cylinder. Seven genes homologous to AtPHO1 (PpPHO1;1-PpPHO1;7) have been identified in the moss Physcomitrella patens. The corresponding proteins harbor an SPX tripartite domain in the N-terminal hydrophilic portion and an EXS domain in the conserved C-terminal hydrophobic portion, both common features of the plant PHO1 family. Northern-blot analysis showed distinct expression patterns for the PpPHO1 genes, both at the tissue level and in response to phosphate deficiency. Transgenic P. patens expressing the beta-glucuronidase reporter gene under three different PpPHO1 promoters revealed distinct expression profiles in various tissues. Expression of PpPHO1;1 and PpPHO1;7 was specifically induced by Pi starvation. P. patens homologs to the Arabidopsis PHT1, DGD2, SQD1, and APS1 genes also responded to Pi deficiency by increased mRNA levels. Morphological changes associated with Pi deficiency included elongation of caulonemata with inhibition of the formation of side branches, resulting in colonies with greater diameter, but reduced mass compared to Pi-sufficient plants. Under Pi-deficient conditions, P. patens also increased the synthesis of ribonucleases and of an acid phosphatase, and increased the ratio of sulfolipids over phospholipids. These results indicate that P. patens and higher plants share some common strategies to adapt to Pi deficiency, although morphological changes are distinct, and that the PHO1 proteins are well conserved in bryophyte despite the lack of a developed vascular system.

Uncoupling phosphate deficiency from its major effects on growth and transcriptome via PHO1 expression in Arabidopsis.

Inorganic phosphate (Pi) is one of the most limiting nutrients for plant growth in both natural and agricultural contexts. Pi-deficiency leads to a strong decrease in shoot growth, and triggers extensive changes at the developmental, biochemical and gene expression levels that are presumably aimed at improving the acquisition of this nutrient and sustaining growth. The Arabidopsis thaliana PHO1 gene has previously been shown to participate in the transport of Pi from roots to shoots, and the null pho1 mutant has all the hallmarks associated with shoot Pi deficiency. We show here that A. thaliana plants with a reduced expression of PHO1 in roots have shoot growth similar to Pi-sufficient plants, despite leaves being strongly Pi deficient. Furthermore, the gene expression profile normally triggered by Pi deficiency is suppressed in plants with low PHO1 expression. At comparable levels of shoot Pi supply, the wild type reduces shoot growth but maintains adequate shoot vacuolar Pi content, whereas the PHO1 underexpressor maintains maximal growth with strongly depleted Pi reserves. Expression of the Oryza sativa (rice) PHO1 ortholog in the pho1 null mutant also leads to plants that maintain normal growth and suppression of the Pi-deficiency response, despite the low shoot Pi. These data show that it is possible to unlink low shoot Pi content with the responses normally associated with Pi deficiency through the modulation of PHO1 expression or activity. These data also show that reduced shoot growth is not a direct consequence of Pi deficiency, but is more likely to be a result of extensive gene expression reprogramming triggered by Pi deficiency.

Regulatory roles of the GacS/GacA two-component system in plant-associated and other gram-negative bacteria.

The sensor kinase GacS and the response regulator GacA are members of a two-component system that is present in a wide variety of gram-negative bacteria and has been studied mainly in enteric bacteria and fluorescent pseudomonads. The GacS/GacA system controls the production of secondary metabolites and extracellular enzymes involved in pathogenicity to plants and animals, biocontrol of soilborne plant diseases, ecological fitness, or tolerance to stress. A current model proposes that GacS senses a still-unknown signal and activates, via a phosphorelay mechanism, the GacA transcription regulator, which in turn triggers the expression of target genes. The GacS protein belongs to the unorthodox sensor kinases, characterized by an autophosphorylation, a receiver, and an output domain. The periplasmic loop domain of GacS is poorly conserved in diverse bacteria. Thus, a common signal interacting with this domain would be unexpected. Based on a comparison with the transcriptional regulator NarL, a secondary structure can be predicted for the GacA sensor kinases. Certain genes whose expression is regulated by the GacS/GacA system are regulated in parallel by the small RNA binding protein RsmA (CsrA) at a posttranscriptional level. It is suggested that the GacS/GacA system operates a switch between primary and secondary metabolism, with a major involvement of posttranscriptional control mechanisms.

Expression analyses of three members of the AtPHO1 family reveal differential interactions between signaling pathways involved in phosphate deficiency and the responses to auxin, cytokinin, and abscisic acid.

The PHO1 protein is involved in loading inorganic phosphate (Pi) to the root xylem. Ten genes homologous to AtPHO1 are present in the Arabidopsis thaliana (L.) Heyn genome. From this gene family, transcript levels of only AtPHO1, AtPHO1;H1 and AtPHO1;H10 were increased by Pi-deficiency. While the up-regulation of AtPHO1;H1 and AtPHO1;H10 by Pi deficiency followed the same rapid kinetics and was dependent on the PHR1 transcription factor, phosphite only strongly suppressed the expression of AtPHO1;H1 and had a minor effect on AtPHO1;H10. Addition of sucrose was found to increase transcript levels of both AtPHO1 and AtPHO1;H1 in Pi-sufficient or Pi-deficient plants, but to suppress AtPHO1:H10 under the same conditions. Treatments of plants with auxin or cytokinin had contrasting effect depending on the gene and on the Pi status of the plants. Thus, while both hormones down-regulated expression of AtPHO1 independently of the plant Pi status, auxin and cytokinin up-regulated AtPHO1;H1 and AtPHO1;H10 expression in Pi-sufficient plants and down-regulated expression in Pi-deficient plants. Treatments with abscisic acid inhibited AtPHO1 and AtPHO1;H1 expression in both Pi-sufficient and Pi-deficient plants, but increased AtPHO1;H10 expression under the same conditions. The inhibition of expression by abscisic acid of AtPHO1 and AtPHO1;H1, and of the Pi-starvation responsive genes AtPHT1;1 and AtIPS1, was dependant on the ABI1 type 2C protein phosphatase. These results reveal that various levels of cross talk between the signal transduction pathways to Pi, sucrose and phytohormones are involved in the regulation of expression of the three AtPHO1 homologues.

Les biomarqueurs dans la maladie de Fabry: relation entre Sphingosine-1 phosphate et Lyso-Gb3

Problématique : La maladie de Fabry est une maladie métabolique à stockage lysosomal. C'est une maladie héreditaire à transmission récessive qui concerne l'enzyme alpha-Galactosidase A. Le gène de l'alpha-Galactosidase A (GLA) se trouve au niveau du bras long du chromosome X «carté en Xq21.33-Xq22 ». L'enzyme muté ne recouvre plus son rôle catabolisateur et il ne métabolise pas le substrat globotriaosylceramide (Gb3). Par conséquence le Gb3 s'accumule dans tous les tissus. Dans les parois des vaisseaux sanguins le Gb3 s'accumule dans l'endothelium, la tunique interne des vaisseaux sanguins. Ce déficit métabolique se traduit par l'épaississement de la paroi vasculaire, des processus d'infarctus et ischémies du tissu cardiaque, rénal et cérébral. L'implication cardiaque de la maladie de Fabry est décrite chez plus de 78% des patients affectés par la maladie et se manifeste par une hypertrophie cardiaque du ventricule gauche. Toutefois, il n'existe pas de relation étroite entre hypertrophie cardiaque et le Gb3. La sphingosine 1-phosphate à été identifiée dans notre laboratoire et proposée comme facteur de croissance à l'origine du remodelage cardiovasculaire. De plus, la Globotriaosylsphingosine (Lyso-Gb3) à été aussi proposée comme facteur vasoactif chez les patients Fabry. Objectif : L'identification d'un biomarqueur pour le diagnostic et le suivi thérapeutique de la maladie de Fabry représente une domaine d'investigation active en recherche scientifique. Le Gb3 plasmatique ou dans les urines, la biopsie rénale ou cardiaque qui est mis en évidence grâce à la microscopie électronique sous forme de corps concentrique lamellaires, constituent les biomarqueurs classiques de la maladie de Fabry. Dernièrement, le Lyso-Gb3 et le Sphingosine-1 phosphate (S1P) ont été proposés comme marqueurs du remodelage cardiovasculaire. Le but de ce travail est de rassembler et de discuter la littérature concernant ces nouveaux marqueurs et, d'étudier une possible interaction entre Lyso-Gb3 et le S1P. Méthodologie : Rassembler la littérature scientifique et analyser l'implication de ces marqueurs dans la maladie de Fabry et leur effets cardiovasculaires. De plus, un travail expérimental est effectué. Ce travail consiste en l'identification d'une relation possible entre le Lyso-Gb3 et le S1P. Résultats : Avec ce travail on a cherché à actualiser et mettre à jour les notions concernant les biomarqueurs qui prennent place dans cette pathologie et les connaissances qu'on possède à ce jour sur les manifestations cardiovasculaires et neurologiques.La recherche d'un biomarqueur prime par le fait qu'un nombre considerable de patients est sous-diagnostiqués pour la maladie de Fabry et que entre les taux de substrat enzymatique accumulé dans les tissus et l'hypertrophie cardiaque, on peut constater une discordance. Grâce à ce travail expérimental, on a exclue la possibilité d'un effet précurseur du lyso-Gb3 pour le S1P. Nous avons montré que le Lyso-Gb3 est reconnu par les récepteurs du S1P avec des effets commun pour les S1P1-3 et différents pour le S1P2. Les taux du Lyso-Gb3 et du S1P doivent être mesuré chez les patients Fabry et une stratégie thérapeutique doit prendre en compte le rapport S1P/Lyso-Gb3.

Cell differentiation to "mating bodies" induced by an integrating and conjugative element in free-living bacteria.

Lateral gene transfer (LGT) is one of the most important processes leading to prokaryotic genome innovation. LGT is typically associated with conjugative plasmids and bacteriophages, but recently, a new class of mobile DNA known as integrating and conjugative elements (ICE) was discovered, which is abundant and widespread among bacterial genomes. By studying at the single-cell level the behavior of a prevalent ICE type in the genus Pseudomonas, we uncover the remarkable way in which the ICE orchestrates host cell differentiation to ensure horizontal transmission. We find that the ICE induces a state of transfer competence (tc) in 3%-5% of cells in a population under nongrowing conditions. ICE factors control the development of tc cells into specific assemblies that we name "mating bodies." Interestingly, cells in mating bodies undergo fewer and slower division than non-tc cells and eventually lyse. Mutations in ICE genes disrupting mating-body formation lead to 5-fold decreased ICE transfer rates. Hence, by confining the tc state to a small proportion of the population, ICE horizontal transmission is achieved with little cost in terms of vertical transmission. Given the low transfer frequencies of most ICE, we anticipate regulation by subpopulation differentiation to be widespread.

Human alveolar macrophages infected by virulent bacteria expressing SipB are a major source of active interleukin-18.

Recent publications have demonstrated that the protease caspase-1 is responsible for the processing of pro-interleukin 18 (IL-18) into the active form. Studies on cell lines and murine macrophages have shown that the bacterial invasion factor SipB activates caspase-1, triggering cell death. Thus, we investigated the role of SipB in the activation and release of IL-18 in human alveolar macrophages (AM), which are the first line of defense against inhaled pathogens. Under steady-state conditions, AM are a more important source of IL-18 than are dendritic cells (DC) and monocytes. Cytokine production by AM and DC was compared after both types of cells had been infected with a virulent strain of Salmonella enterica serovar Typhimurium and an isogenic sipB mutant, which were used as an infection model. Infection with virulent Salmonella led to marked cell death with features of apoptosis while both intracellular activation and release of IL-18 were demonstrated. In contrast, the sipB mutant did not induce such cell death or the release of active IL-18. The specific caspase-1 inhibitor Ac-YVAD-CMK blocked the early IL-18 release in AM infected with the virulent strain. However, the type of Salmonella infection did not differentially regulate IL-18 gene expression. We concluded that the bacterial virulence factor SipB plays an essential posttranslational role in the intracellular activation of IL-18 and the release of the cytokine in human AM.

PA21, a New Iron-Based Noncalcium Phosphate Binder, Prevents Vascular Calcification in Chronic Renal Failure Rats.

Chronic renal failure (CRF) is associated with the development of secondary hyperparathyroidism and vascular calcifications. We evaluated the efficacy of PA21, a new iron-based noncalcium phosphate binder, in controlling phosphocalcic disorders and preventing vascular calcifications in uremic rats. Rats with adenine-diet-induced CRF were randomized to receive either PA21 0.5, 1.5, or 5% or CaCO3 3% in the diet for 4 weeks, and were compared with uremic and nonuremic control groups. After 4 weeks of phosphate binder treatment, serum calcium, creatinine, and body weight were similar between all CRF groups. Serum phosphorus was reduced with CaCO3 3% (2.06 mM; P ≤ 0.001), PA21 1.5% (2.29 mM; P < 0.05), and PA21 5% (2.21 mM; P ≤ 0.001) versus CRF controls (2.91 mM). Intact parathyroid hormone was strongly reduced in the PA21 5% and CaCO3 3% CRF groups to a similar extent (1138 and 1299 pg/ml, respectively) versus CRF controls (3261 pg/ml; both P ≤ 0.001). A lower serum fibroblast growth factor 23 concentration was observed in the PA21 5%, compared with CaCO3 3% and CRF, control groups. PA21 5% CRF rats had a lower vascular calcification score compared with CaCO3 3% CRF rats and CRF controls. In conclusion, PA21 was as effective as CaCO3 at controlling phosphocalcic disorders but superior in preventing the development of vascular calcifications in uremic rats. Thus, PA21 represents a possible alternative to calcium-based phosphate binders in CRF patients.

Innate sensors for Gram-positive bacteria.

More than half of invasive bacterial infections are Gram-positive in origin. This class of bacteria has neither endotoxins nor an outer membrane, yet it generates some of the most powerful inflammatory responses known in medicine. Some recent seminal studies go a long way toward settling the controversies that surround the process by which Gram-positive bacterial surfaces trigger the human immune system. Although the components of the cell wall are now chemically defined in exquisite detail and the interaction with the toll-like receptor 2 pathway has been discovered, it is only very recently that definitive studies combining these advanced biochemical and cell biological tools have been carried out. It is these breakthrough studies that have finally confirmed the paradigm of innate sensors for Gram-positive bacteria.