The genetic diversity of 221 Mimosa pudica bacterial symbionts trapped from eight soils from diverse environments in French Guiana was assessed by 16S rRNA PCR-RFLP, REP-PCR fingerprints, as well as by phylogenies of their 16S rRNA and recA housekeeping genes, and by their nifH, nodA and nodC symbiotic genes. Interestingly, we found a large diversity of beta-rhizobia, with Burkholderia phymatum and Burkholderia tuberum being the most frequent and diverse symbiotic species. Other species were also found, such as Burkholderia mimosarum, an unnamed Burkholderia species and, for the first time in South America, Cupriavidus taiwanensis. The sampling site had a strong influence on the diversity of the symbionts sampled, and the specific distributions of symbiotic populations between the soils were related to soil composition in some cases. Some alpha-rhizobial strains taxonomically close to Rhizobium endophyticum were also trapped in one soil, and these carried two copies of the nodA gene, a feature not previously reported. Phylogenies of nodA, nodC and nifH genes showed a monophyly of symbiotic genes for beta-rhizobia isolated from Mimosa spp., indicative of a long history of interaction between beta-rhizobia and Mimosa species. Based on their symbiotic gene phylogenies and legume hosts, B. tuberum was shown to contain two large biovars: one specific to the mimosoid genus Mimosa and one to South African papilionoid legumes.

Both active and passive immunization strategies against Staphylococcus aureus have thus far failed to show efficacy in humans. With the attempt to develop an effective S. aureus vaccine, we selected five conserved antigens known to have different roles in S. aureus pathogenesis. They include the secreted factors α-hemolysin (Hla), ess extracellular A (EsxA), and ess extracellular B (EsxB) and the two surface proteins ferric hydroxamate uptake D2 and conserved staphylococcal antigen 1A. The combined vaccine antigens formulated with aluminum hydroxide induced antibodies with opsonophagocytic and functional activities and provided consistent protection in four mouse models when challenged with a panel of epidemiologically relevant S. aureus strains. The importance of antibodies in protection was demonstrated by passive transfer experiments. Furthermore, when formulated with a toll-like receptor 7-dependent (TLR7) agonist recently designed and developed in our laboratories (SMIP.7-10) adsorbed to alum, the five antigens provided close to 100% protection against four different staphylococcal strains. The new formulation induced not only high antibody titers but also a Th1 skewed immune response as judged by antibody isotype and cytokine profiles. In addition, low frequencies of IL-17-secreting T cells were also observed. Altogether, our data demonstrate that the rational selection of mixtures of conserved antigens combined with Th1/Th17 adjuvants can lead to promising vaccine formulations against S. aureus.Staphylococcus aureus | vaccine | TLR7 | adjuvant | Hla C urrent antibiotics are not efficacious against emerging multidrug-resistant strains of Staphylococcus aureus, a major human pathogen. Therefore, there is an urgent need to develop vaccines to target this pathogen. Two prophylactic vaccines have been tested recently for efficacy in humans: StaphVAX, which contained capsular polysaccharides type 5 and 8 (CP5 and CP8), and V710, based on a single protein antigen (IsdB) (1, 2). Both vaccines failed in phase III efficacy trials (3, 4). On the basis of these disappointing results and taking into account that S. aureus produces a plethora of virulence and immune evasion factors, different vaccine candidates, constituted by multiple components, are currently in phase I/II trials, but efficacy data are not available yet (5). In line with the multicomponent strategy, our laboratory has undertaken a vaccine discovery project aiming at the identification of conserved antigens, which play important roles in S. aureus virulence and pathogenicity. The main objective of the study was to combine the selected antigens in the presence of appropriate adjuvants and to demonstrate protective efficacy against a panel of genetically different S. aureus clinical isolates in different mouse models. ResultsAntigen Selection. The antigens included in our candidate combination vaccine were selected among surface and secreted factors previously shown to be protective and involved in S. aureus virulence. Two of them, the ferric hydroxamat...

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Iron availability plays an essential role in staphylococcal pathogenesis. We selected FhuD2, a lipoprotein involved in iron-hydroxamate uptake, as a novel vaccine candidate against Staphylococcus aureus. Unprecedented for staphylococcal lipoproteins, the protein was demonstrated to have a discrete, punctate localization on the bacterial surface. FhuD2 vaccination generated protective immunity against diverse clinical S. aureus isolates in murine infection models. Protection appeared to be associated with functional antibodies that were shown to mediate opsonophagocytosis, to be effective in passive transfer experiments, and to potentially block FhuD2-mediated siderophore uptake. Furthermore, the protein was found to be up-regulated in infected tissues and was required for staphylococcal dissemination and abscess formation. Herein we show that the staphylococcal iron-hydroxamate uptake system is important in invasive infection and functions as an efficacious vaccine target.

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Qualitative and quantitative estimation of phenolic compounds was done through reverse phase-high performance liquid chromatography (RP-HPLC) from different parts (leaf, stem, and root) of rice plants after inoculation with two rhizobial strains, RRE6 (Rhizobium leguminosarum bv. phaseoli) and ANU 843 (R. leguminosarum bv. trifolii) and infection by Rhizoctonia solani. On the basis of their retention time, the major phenolic acids detected in HPLC analysis were gallic, tannic, ferulic, and cinnamic acids. Furthermore, in all Rhizobium-inoculated rice plants, synthesis of phenolic compounds was more consistently enhanced than in control (uninoculated plants), where the maximum accumulation of phenolic compounds was observed in plants inoculated with RRE6 and infection with R. solani. Under pathogenic stress, RRE6 performed better because a relatively higher amount of phenolics was induced as compared with plants treated with ANU 843. Phenolic acids mediate induced systemic resistance and provide bioprotection to plants during pathogenic stresses. In addition, both rhizobial strains promote growth and productivity of rice plants in greenhouse conditions. This report on Rhizobium-mediated defense responses and growth promotion of nonlegume (such as rice) provides a novel paradigm of symbiotic plant-microbe interaction.

Staphylococcus aureus is a human pathogen causing globally significant morbidity and mortality. The development of antibiotic resistance in S. aureus highlights the need for a preventive vaccine. In the present paper we explore the structure and function of FhuD2 (ferric-hydroxamate uptake D2), a staphylococcal surface lipoprotein mediating iron uptake during invasive infection, recently described as a promising vaccine candidate. Differential scanning fluorimetry and calorimetry studies revealed that FhuD2 is stabilized by hydroxamate siderophores. The FhuD2-ferrichrome interaction was of nanomolar affinity in surface plasmon resonance experiments and fully iron(III)-dependent. We determined the X-ray crystallographic structure of ligand-bound FhuD2 at 1.9 Å (1 Å=0.1 nm) resolution, revealing the bilobate fold of class III SBPs (solute-binding proteins). The ligand, ferrichrome, occupies a cleft between the FhuD2 N- and C-terminal lobes. Many FhuD2-siderophore interactions enable the specific recognition of ferrichrome. Biochemical data suggest that FhuD2 does not undergo significant conformational changes upon siderophore binding, supporting the hypothesis that the ligand-bound complex is essential for receptor engagement and uptake. Finally, immunizations with FhuD2 alone or FhuD2 formulated with hydroxamate siderophores were equally protective in a murine staphylococcal infection model, confirming the suitability and efficacy of apo-FhuD2 as a protective antigen, and suggesting that other class III SBPs might also be exploited as vaccine candidates.

Vaccine research and development are experiencing a renaissance of interest from the global scientific community. There are four major reasons for this: (1) the lack of efficacious treatment for many devastating infections; (2) the emergence of multidrug resistant bacteria; (3) the need for improving the safety of the more traditional licensed vaccines; and finally, (4) the great promise for innovative vaccine design and research with convergence of omics sciences, such as genomics, proteomics, immunomics, and vaccinology. Our first project based on omics was initiated in 2000 and was termed reverse vaccinology. At that time, antigen identification was mainly based on bioinformatic analysis of a singular genome. Since then, omics-guided approaches have been applied to its full potential in several proof-of-concept studies in the industry, with the first reverse vaccinology-derived vaccine now in late stage clinical trials and several vaccines developed by omics in preclinical studies. In the meantime, vaccine discovery and development has been further improved with the support of proteomics, functional genomics, comparative genomics, structural biology, and most recently vaccinomics. We illustrate in this review how omics biotechnologies and integrative biology are expected to accelerate the identification of vaccine candidates against difficult pathogens for which traditional vaccine development has thus far been failing, and how research will provide safer vaccines and improved formulations for immunocompromised patients in the near future. Finally, we present a discussion to situate omics-guided rational vaccine design in the broader context of global public health and how it can benefit citizens in both developed and developing countries.