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The supply of soluble silicon (Si) to plants has been associated with many benefits that remain poorly explained and often contested. In this work, the effect of Si was studied on wheat plants under both control and pathogen stress (Blumeria graminis f. sp. tritici) conditions by conducting a large transcriptomic analysis (55,000 unigenes) aimed at comparing the differential response of plants under four treatments. The response to the supply of Si on control (uninfected) plants was limited to 47 genes of diverse functions providing little evidence of regulation of a specific metabolic process. Plants reacted to inoculation with B. graminis f. sp. tritici by an upregulation of many genes linked to stress and metabolic processes and a downregulation of genes linked to photosynthesis. Supplying Si to inoculated plants largely prevented disease development, a phenotypic response that translated into a nearly perfect reversal of genes regulated by the effect of B. graminis f. sp. tritici alone. These results suggest that Si plays a limited role on a plant's transcriptome in the absence of stress, even in the case of a high-Si-accumulating monocot such as wheat. On the other hand, the benefits of Si in the form of biotic stress alleviation were remarkably aligned with a counter-response to transcriptomic changes induced by the pathogen B. graminis f. sp. tritici.

Soluble silicon, absorbed in the form of silicic acid by plant roots, confers efficient protection against many diseases. However, owing to its low solubility, there is a practical limit to increasing silicic acid availability to plants in the field. For this reason, methyl silanols – mono-, di- and trimethyl silicic acid – the water-soluble degradation products of silicone polymer, were evaluated for their ability to protect against powdery mildew in wheat grown under peat-based and hydroponic conditions. X-ray microanalysis indicated that only the monomethyl derivative was absorbed and deposited by wheat plants. Inductively coupled plasma–optical emission spectrometry measurements of total plant Si content confirmed this observation and indicated that monomethyl silicic acid remained mostly in its soluble monomeric form in planta. Mono- and trimethyl silicic acid offered no protection against powdery mildew and, indeed, yielded higher levels of infection than the control. Unexpectedly, dimethyl silicic acid induced severe symptoms of phytotoxicity early into the experiments at nutrient solution concentrations as low as 0.1 mM. For their part, both mono- and trimethyl silicic acid also caused symptoms of phytotoxicity by the end of the experiments. Our findings would suggest that silanols cannot be considered as substitutes for silicic acid in plants. Moreover, application of silicone-contaminated waste or sewage sludge to agricultural land needs to be evaluated with considerable care.

International audience; Probiotic formulations are widely used and are proposed to have a variety of beneficial effects, depending on the probiotic strains present in the product. The impact of drying processes on the viability of probiotics is well documented. However, the impact of these processes on probiotics functionality remains unclear. In this work, we investigated variations in seven different bacterial markers after various desiccation processes. Markers were composed of four different viability evaluation (combining two growth abilities and two cytometric measurements) and in three in vitro functionalities: stimulation of IL-10 and IL-12 production by PBMCs (immunomodulation) and bacterial adhesion to hexadecane. We measured the impact of three drying processes (air-drying, freeze-drying and spray-drying), without the use of protective agents, on three types of probiotic bacteria: Bifidobacterium bifidum, Lactobacillus plantarum and Lactobacillus zeae. Our results show that the bacteria respond differently to the three different drying processes, in terms of viability and functionality. Drying methods produce important variations in bacterial immunomodulation and hydrophobicity, which are correlated. We also show that adherence can be stimulated (air-drying) or inhibited (spray-drying) by drying processes. Results of a multivariate analysis show no direct correlation between bacterial survival and functionality, but do show a correlation between probiotic responses to desiccation–rewetting and the process used to dry the bacteria.

Chronic intestinal inflammation alters host physiology and could lead to colorectal cancer (CRC). We have previously reported beneficial effects of the probiotic strain of Lactobacillus casei BL23 in different murine models of intestinal inflammation. In addition, there is an emerging interest on the potential beneficial effects of probiotics to treat CRC. We thus explored whether L. casei BL23 displays protective effects on CRC.Mice were subcutaneously injected with 1,2-dimethylhydrazine (DMH) weekly during 10 weeks and orally administered with L. casei BL23 in the drinking water until the 10th week. Multiple plaque lesions in the large intestine were observed macroscopically and counted and intestinal tissues were also histologically analyzed. Finally, T-cell populations and cytokine production were evaluated after co-incubation of L. casei BL23 with spleen cells from non-treated mice to determine the immuno-modulatory effects of this bacterium.Our results show that oral treatment with this probiotic bacterium modulates host immune responses and significantly protect mice against DMH-induced CRC. This protection may be associated with the modulation of regulatory T-cells towards a Th17-biased immune response accompanied by the expression of regulatory cytokines (IL-6, IL-17, IL-10 and TGF-β), as demonstrated in L. casei BL23-treated splenocytes, but also with the colonic expression of IL-22 observed in vivo on L. casei BL23-treated mice; suggesting the induction of a fine-tune Th17-biased response.Altogether our results reveal the high potential of L. casei BL23 to treat CRC and opens new frontiers for the study of immunomodulatory functions of probiotics.

Bovine mastitis is a costly disease in dairy cattle worldwide. As of yet, the control of bovine mastitis is mostly based on prevention by thorough hygienic procedures during milking. Additional strategies include vaccination and utilization of antibiotics. Despite these measures, mastitis is not fully under control, thus prompting the need for alternative strategies. The goal of this study was to isolate autochthonous lactic acid bacteria (LAB) from bovine mammary microbiota that exhibit beneficial properties that could be used for mastitis prevention and/or treatment. Sampling of the teat canal led to the isolation of 165 isolates, among which a selection of ten non-redundant LAB strains belonging to the genera Lactobacillus and Lactococcus were further characterized with regard to several properties: surface properties (hydrophobicity, autoaggregation); inhibition potential of three main mastitis pathogens, Staphylococcus aureus, Escherichia coli and Streptococcus uberis; colonization capacities of bovine mammary epithelial cells (bMEC); and immunomodulation properties. Three strains, Lactobacillus brevis 1595 and 1597 and Lactobacillus plantarum 1610, showed high colonization capacities and a medium surface hydrophobicity. These strains are good candidates to compete with pathogens for mammary gland colonization. Moreover, nine strains exhibited anti-inflammatory properties, as illustrated by the lower IL-8 secretion by E. coli-stimulated bMEC in the presence of these LAB. Full genome sequencing of five candidate strains allowed to check for undesirable genetic elements such as antibiotic resistance genes and to identify potential bacterial determinants involved in the beneficial properties. This large screening of beneficial properties while checking for undesirable genetic markers allowed the selection of promising candidate LAB strains from bovine mammary microbiota for the prevention and/or treatment of bovine mastitis. Fil: Bouchard, Damien S.. Institut National de la Recherche Agronomique; Francia. Agrocampus Ouest; Francia Fil: Seridan, Bianca. Universidade Federal de Minas Gerais; Brasil. Institut National de la Recherche Agronomique; Francia. Agrocampus Ouest; Francia Fil: Saraoui, Taous. Institut National de la Recherche Agronomique; Francia. Agrocampus Ouest; Francia Fil: Rault, Lucie. Institut National de la Recherche Agronomique; Francia. Agrocampus Ouest; Francia Fil: Germon, Pierre. Institut National de la Recherche Agronomique; Francia Fil: Gonzalez Moreno, Candelaria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Centro de Referencia para Lactobacilos; Argentina Fil: Nader, Maria Elena Fatima. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Centro de Referencia para Lactobacilos; Argentina Fil: Baud, Damien. Geneva University Hospital. Genomic Research Laboratory ; Suiza Fil: François, Patrice. Geneva University Hospital. Genomic Research Laboratory ; Suiza Fil: Chuat, Victoria. Institut National de la Recherche Agronomique; Francia. Agrocampus Ouest; Francia Fil: Chain, Florian. Institut National de la Recherche Agronomique; Francia Fil: Langella, Philippe. Institut National de la Recherche Agronomique; Francia Fil: Nicoli, Jacques. Universidade Federal de Minas Gerais; Brasil Fil: Le Loir, Yves. Institut National de la Recherche Agronomique; Francia. Agrocampus Ouest; Francia Fil: Even, Sergine. Institut National de la Recherche Agronomique; Francia. Agrocampus Ouest; Francia

Faecalibacterium prausnitzii is an anti-inflammatory commensal bacterium identified on the basis of human clinical data. The mechanisms underlying its beneficial effects are still unknown. Gnotobiotic mice harboring F. prausnitzii (A2-165) and Escherichia coli (K-12 JM105) were subjected to 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced acute colitis. The inflammatory colitis scores and a gas chromatography-time of flight (GC/TOF) mass spectrometry-based metabolomic profile were monitored in blood, ileum, cecum, colon, and feces in gnotobiotic mice. The potential anti-inflammatory metabolites were tested in vitro. We obtained stable E. coli and F. prausnitzii-diassociated mice in which E. coli primed the gastrointestinal tract (GIT), allowing a durable and stable establishment of F. prausnitzii. The disease activity index, histological scores, myeloperoxidase (MPO) activity, and serum cytokine levels were significantly lower in the presence of F. prausnitzii after TNBS challenge. The protective effect of F. prausnitzii against colitis was correlated to its implantation level and was linked to overrepresented metabolites along the GIT and in serum. Among 983 metabolites in GIT samples and serum, 279 were assigned to known chemical reactions. Some of them, belonging to the ammonia (α-ketoglutarate), osmoprotective (raffinose), and phenolic (including anti-inflammatory shikimic and salicylic acids) pathways, were associated with a protective effect of F. prausnitzii, and the functional link was established in vitro for salicylic acid. We show for the first time that F. prausnitzii is a highly active commensal bacterium involved in reduction of colitis through in vivo modulation of metabolites along the GIT and in the peripheral blood., IMPORTANCE Inflammatory bowel diseases (IBD) are characterized by low proportions of F. prausnitzii in the gut microbiome. This commensal bacterium exhibits anti-inflammatory effects through still unknown mechanisms. Stable monoassociated rodents are actually not a reproducible model to decipher F. prausnitzii protective effects. We propose a new gnotobiotic rodent model providing mechanistic clues. In this model, F. prausnitzii exhibits protective effects against an acute colitis and a protective metabolic profile is linked to its presence along the digestive tract. We identified a molecule, salicylic acid, directly involved in the protective effect of F. prausnitzii. Targeting its metabolic pathways could be an attractive therapeutic strategy in IBD.

Background The human gut houses one of the most complex and abundant ecosystems composed of up to 1013-1014 microorganisms. The importance of this intestinal microbiota is highlighted when a disruption of the intestinal ecosystem equilibrium appears (a phenomenon called dysbiosis) leading to an illness status, such as inflammatory bowel diseases (IBD). Indeed, the reduction of the commensal bacterium Faecalibacterium prausnitzii (one of the most prevalent intestinal bacterial species in healthy adults) has been correlated with several diseases, including IBD, and most importantly, it has been shown that this bacterium has anti-inflammatory and protective effects in pre-clinical models of colitis. Some dysbiosis disorders are characterized by functional and physiological alterations. Here, we report the beneficial effects of F. prausnitzii in the physiological changes induced by a chronic low-grade inflammation in a murine model. Chronic low-grade inflammation and gut dysfunction were induced in mice by two episodes of dinitro-benzene sulfonic acid (DNBS) instillations. Markers of inflammation, gut permeability, colonic serotonin and cytokine levels were studied. The effects of F. prausnitzii strain A2-165 and its culture supernatant (SN) were then investigated. Results No significant differences were observed in classical inflammation markers confirming that inflammation was subclinical. However, gut permeability, colonic serotonin levels and the colonic levels of the cytokines IL-6, INF-γ, IL-4 and IL-22 were higher in DNBS-treated than in untreated mice. Importantly, mice treated with either F. prausnitzii or its SN exhibited significant decreases in intestinal permeability, tissue cytokines and serotonin levels. Conclusions Our results show that F. prausnitzii and its SN had beneficial effects on intestinal epithelial barrier impairment in a chronic low-grade inflammation model. These observations confirm the potential of this bacterium as a novel probiotic treatment in the management of gut dysfunction and low-grade inflammation. Electronic supplementary material The online version of this article (doi:10.1186/s12866-015-0400-1) contains supplementary material, which is available to authorized users.

Erratum to: Microb Cell Fact (2015) 14:176 DOI 10.1186/s12934-015-0367-5 author Yolande Chvatchko was incorrectly included as Yolande Chvatchenko; International audience; Background: Thymic stromal lymphopoietin (TSLP) is a cytokine known to mature dendritics cells, lower pro-inflammatory IL-12 secretion, induce differentiation of anti-inflammatory FoxP3+ regulatory T cells (Treg). Moreover, Crohn's disease patients have shown a reduction of intestinal TSLP expression. To understand the role of TSLP in inflammation, we constructed Lactococcus lactis strain producing TSLP (LL-TSLP) and investigated the effect of its administration on dextran sulfate sodium (DSS)-induced colitis model in mice. Results: LL-TSLP secrete an active molecule which lowers secretion of IL-12 by dendritic cells. Treatment with LL-TSLP, increases the amount of TGF-beta secreted by T cells in Mesenteric Lymph Node in healthy mice. In acute DSS-induced colitis, LL-TSLP delayed the Disease Activity Index and lowered histological score and colonic INF-gamma production. In a DSS-recovery model, LL-TSLP induced a better protective effect if the strain was administered at the beginning of the colitis. At Day 4 of colitis we observed an induction of Treg by LL-TSLP. Conclusions: TSLP showed an anti-inflammatory protective role in DSS-induced colitis. We have demonstrated that a short and early administration of LL-TSLP is more efficient than a long lasting treatment.

International audience; Abstract Impaired gut barrier function has been reported in a wide range of diseases and syndromes and in some functional gastrointestinal disorders. In addition, there is increasing evidence that suggests the gut microbiota tightly regulates gut barrier function and recent studies demonstrate that probiotic bacteria can enhance barrier integrity. Here, we aimed to investigate the effects of Lactobacillus rhamnosus CNCM I-3690 on intestinal barrier function. In vitro results using a Caco-2 monolayer cells stimulated with TNF-α confirmed the anti-inflammatory nature of the strain CNCM I-3690 and pointed out a putative role for the protection of the epithelial function. Next, we tested the protective effects of L. rhamnosus CNCM I-3690 in a mouse model of increased colonic permeability. Most importantly, we compared its performance to that of the well-known beneficial human commensal bacterium Faecalibacterium prauznitzii A2-165. Increased colonic permeability was normalized by both strains to a similar degree. Modulation of apical tight junction proteins expression was then analyzed to decipher the mechanism underlying this effect. We showed that CNCM I-3690 partially restored the function of the intestinal barrier and increased the levels of tight junction proteins Occludin and E-cadherin. The results indicate L. rhamnosus CNCM I-3690 is as effective as the commensal anti-inflammatory bacterium F. prausnitzii to treat functional barrier abnormalities.

International audience; Barley yellow dwarf (BYD) is one of the main viral diseases of small-grain cereals. This disease, reported on numerous plant species of the Poaceae family, is caused by a complex of eight viral species including the species Barley Yellow Dwarf Virus-PAV (BYDV-PAV), frequently found in western Europe. Resistance sources against BYDV-PAV are scarce and only identified in perennial Triticineae. Some BYDV-resistant wheat lines have been obtained by introgressing these resistances into bread wheat germplasms. Genetic and biological characterization of the resulting lines has been undertaken. However, little information on the resistant behaviour of these lines during the early stages of the infection process is available. To evaluate the resistance of two genetically distinct resistant lines (Zhong ZH and TC14), 1740 young plantlets, belonging to susceptible reference hosts (barley cv. Express and wheat cv. Sunstar), Zhong ZH or TC14 wheat lines, were inoculated in controlled conditions with French BYDV-PAV isolates. The infection process was monitored during the first 21 days after inoculation (DAI) using a semi-quantitative ELISA. A standardized protocol including five successive samplings of leaves from all inoculated plants and the collection of plant roots at the end of the monitored period was carried out. This protocol enabled an assessment of the infection percentage and the evolution of the viral load in plants from the 7th DAI to the 21st DAI. Statistical analyses of the BYDV infection kinetics using raw ELISA data, a model of the time-dependent variation of the percentage of infected plants and the area under concentration progress curves (AUCPC) demonstrated that Zhong ZH and TC14 lines (1) reduce the development rate of the BYD disease during the first days of infection, (2) decrease the infection efficiency of BYDV-PAV isolates, in the leaves, from 98.7% for susceptible plant genotypes to 81.9% and 71.7% for Zhong ZH and TC14, respectively, (3) reduce the virus load in the leaves of infected plants and (4) are not spared from BYDV infection, as 95.1% of Zhong ZH and 90.2% of TC14 inoculated plants accumulated viral particles in roots and/or in leaves at 21 DAI. These results confirm the BYDV-partial resistant behaviour of both Zhong ZH and TC14 lines. The development rate of the disease was the single parameter that allowed the distinction between the two resistant sources present in the tested lines

International audience; Background Crohn’s disease (CD)-associated dysbiosis is characterised by a loss of Faecalibacterium prausnitzii, whose culture supernatant exerts an anti-inflammatory effect both in vitro and in vivo. However, the chemical nature of the anti-inflammatory compounds has not yet been determined.Methods Peptidomic analysis using mass spectrometry was applied to F. prausnitzii supernatant. Anti-inflammatory effects of identified peptides were tested in vitro directly on intestinal epithelial cell lines and on cell lines transfected with a plasmid construction coding for the candidate protein encompassing these peptides. In vivo, the cDNA of the candidate protein was delivered to the gut by recombinant lactic acid bacteria to prevent dinitrobenzene sulfonic acid (DNBS)-colitis in mice.Results The seven peptides, identified in the F. prausnitzii culture supernatants, derived from a single microbial anti-inflammatory molecule (MAM), a protein of 15 kDa, and comprising 53% of non-polar residues. This last feature prevented the direct characterisation of the putative anti-inflammatory activity of MAM-derived peptides. Transfection of MAM cDNA in epithelial cells led to a significant decrease in the activation of the nuclear factor (NF)-κB pathway with a dose-dependent effect. Finally, the use of a food-grade bacterium, Lactococcus lactis, delivering a plasmid encoding MAM was able to alleviate DNBS-induced colitis in mice.Conclusions A 15 kDa protein with anti-inflammatory properties is produced by F. prausnitzii, a commensal bacterium involved in CD pathogenesis. This protein is able to inhibit the NF-κB pathway in intestinal epithelial cells and to prevent colitis in an animal model.

International audience; : Irritable bowel syndrome (IBS) is a gastrointestinal disorder characterized by chronic abdominal pain, discomfort, and bloating. Interestingly, there is now evidence of the presence of a low grade inflammation status in many IBS patients, including histopathological and mucosal cytokine levels in the colon, as well as the presence of IBS-like symptoms in quiescent inflammatory bowel disease (IBD). The use of a genetically engineered food-grade bacterium, such as Lactococcus lactis, secreting the anti-inflammatory cytokine IL-10 has been proven by many pre-clinical studies to be a successful therapy to treat colon inflammation. In this study, we first reproduced the recovery-recurrence periods observed in IBS-patients in a new chronic model characterized by two episodes of DiNitro-BenzeneSulfonic-acid (DNBS)-challenge and we tested the effects of a recombinant strain of L. lactis secreting IL-10 under a Stress-Inducible Controlled Expression (SICE) system. In vivo gut permeability, colonic serotonin levels, cytokine profiles and spleen cell populations were then measured as readouts of a low-grade inflammation. In addition, since there is increasing evidence that gut microbiota tightly regulates gut barrier function, tight junction proteins were also measured by qRT-PCR after administration of recombinant L. lactis in DNBS-treated mice. Strikingly, oral administration of L. lactis secreting active IL-10 in mice resulted in significant protective effects in terms of permeability, immune activation and gut-function parameters. Although genetically engineered bacteria are, for now, used only as a "proof of concept," our study validates the interest in the use of the novel SICE system in L. lactis to express therapeutic molecule, such as IL-10, locally at mucosal surfaces.

The aims of this study were to develop strains of lactic acid bacteria (LAB) having both immunomodulatory and antioxidant properties and to evaluate their anti-inflammatory effects both in vitro , in different cellular models, and in vivo , in a mouse model of colitis. Different Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains were cocultured with primary cultures of mononuclear cells. Analysis of the pro- and anti-inflammatory cytokines secreted by these cells after coincubation with candidate bacteria revealed that L. delbrueckii subsp. bulgaricus CRL 864 and S. thermophilus CRL 807 display the highest anti-inflammatory profiles in vitro . Moreover, these results were confirmed in vivo by the determination of the cytokine profiles in large intestine samples of mice fed with these strains. S. thermophilus CRL 807 was then transformed with two different plasmids harboring the genes encoding catalase (CAT) or superoxide dismutase (SOD) antioxidant enzymes, and the anti-inflammatory effects of recombinant streptococci were evaluated in a mouse model of colitis induced by trinitrobenzenesulfonic acid (TNBS). Our results showed a decrease in weight loss, lower liver microbial translocation, lower macroscopic and microscopic damage scores, and modulation of the cytokine production in the large intestines of mice treated with either CAT- or SOD-producing streptococci compared to those in mice treated with the wild-type strain or control mice without any treatment. Furthermore, the greatest anti-inflammatory activity was observed in mice receiving a mixture of both CAT- and SOD-producing streptococci. The addition of L. delbrueckii subsp. bulgaricus CRL 864 to this mixture did not improve their beneficial effects. These findings show that genetically engineering a candidate bacterium (e.g., S. thermophilus CRL 807) with intrinsic immunomodulatory properties by introducing a gene expressing an antioxidant enzyme enhances its anti-inflammatory activities.

Comment on : The commensal bacterium Faecalibacterium prausnitzii is protective in DNBS-induced chronic moderate and severe colitis models. [Inflamm Bowel Dis. 2014]; absent

In this study, we developed a large-scale screening of bacterial strains in order to identify novel candidate probiotics with immunomodulatory properties. For this, 158 strains, including a majority of lactic acid bacteria (LAB), were screened by two different cellular models: tumor necrosis factor alpha (TNF-α)-activated HT-29 cells and peripheral blood mononuclear cells (PBMCs). Different strains responsive to both models (pro- and anti-inflammatory strains) were selected, and their protective effects were tested in vivo in a murine model of influenza virus infection. Daily intragastric administrations during 10 days before and 10 days after viral challenge (100 PFU of influenza virus H1N1 strain A Puerto Rico/8/1934 [A/PR8/34]/mouse) of Lactobacillus plantarum CNRZ1997, one potentially proinflammatory probiotic strain, led to a significant improvement in mouse health by reducing weight loss, alleviating clinical symptoms, and inhibiting significantly virus proliferation in lungs. In conclusion, in this study, we have combined two cellular models to allow the screening of a large number of LAB for their immunomodulatory properties. Moreover, we identified a novel candidate probiotic strain, L. plantarum CNRZ1997, active against influenza virus infection in mice.

SUMMARY A standardized single-stranded conformational polymorphism (SSCP) procedure is proposed as an alternative to the timeconsuming biological characterization of Barley yellow dwarf virus-PAV (BYDV-PAV) isolates. Using this procedure, six of 21 overlapping regions used to scan the viral genome gave patterns specific to ‘4E’ (avirulent) or ‘4T’ (‘4E’-derived virulent) isolates. The calibration of samples and integration of SSCP patterns corresponding to the nucleotide region 1482‐2023 allowed the estimation of PT values that reflect the proportions of a ‘4T’specific band. Analysis of the biological (area under the pathogen progress curve) and molecular (PT) data suggested a positive linear relation between these variables. Moreover, sequence analysis of the nucleotide region 1482‐2023 highlighted the presence of a nucleotide polymorphism (C/A1835) which can be considered as a candidate for virus‐host interactions linked to the monitored virulence. According to these parameters, PT values associated with ‘4E’- and ‘4T’-derived populations show that: (i) long-term infection of a BYDV-PAV isolate on the ‘TC14’ resistant host leads to the fixation of virulent individuals in viral populations; and (ii) the introduction of susceptible hosts in successive ‘TC14’ infections results in the maintenance of low virulence of the populations. Thus, the presented study demonstrates that SSCP is a useful tool for monitoring viral populations during the host adaptation process.The described impact of host alternation provides new opportunities for the use of the ‘TC14’ resistance source in BYDV-resistant breeding programmes. This study is part of the global effort made by the scientific community to propose sustainable alternatives to the chemical control of this viral disease.

This study sought to identify the factors and conditions that affected production of the antifungal glycolipid flocculosin by the biocontrol agent Pseudozyma flocculosa. For this purpose, different parameters known or reported to influence glycolipid release in fungi were tested. Concentration of the start-up inoculum was found to play an important role in flocculosin production, as the optimal level increased productivity by as much as tenfold. Carbon availability and nitrogen source (i.e., organic vs inorganic) both had a direct influence on the metabolism of P. flocculosa, leading to flocculosin synthesis. In general, if conditions were conducive for production of the glycolipid, carbon availability appeared to be the only limiting factor. On the other hand, if yeast extract was supplied as nitrogen source, fungal biomass was immediately stimulated to the detriment of flocculosin synthesis. Unlike other reports of glycolipid release by yeast-like fungi, inorganic nitrogen starvation did not trigger production of flocculosin. The relationship between the factors influencing flocculosin production in vitro and the conditions affecting the release of the molecule by P. flocculosa in its natural habitat appears to be linked to the availability of a suitable and plentiful food source for the biocontrol agent.

International audience; Serial passage experiments (SPE) of a Barley yellow dwarf virus-PAV (BYDV-PAV) isolate were performed on Zhong ZH and TC14 wheat lines to evaluate the durability of their resistance to BYDV. At different passage numbers (from the 2nd to the 114th), biological properties of the produced isolates were recorded either by monitoring infection percentages and virus titers of the first 3 weeks of viral infection or by measuring their impact on yield components. Statistical analyses using the area under pathogen progress curves and the area under concentration progress curves demonstrated that these two resistant lines induce, after only a few passages, a selection of variant(s) with significantly modified infection abilities. Isolates resulting from SPE performed on these lines induced important decreases of yield components. These results indicate that the use of Zhong ZH and TC14 lines in BYDV-resistant breeding programmes should be approached with caution

The role and essentiality of silicon (Si) in plant biology have been debated for >150 years despite numerous reports describing its beneficial properties. To obtain unique insights regarding the effect of Si on plants, we performed a complete transcriptome analysis of both control and powdery mildew-stressed Arabidopsis plants, with or without Si application, using a 44K microarray. Surprisingly, the expression of all but two genes was unaffected by Si in control plants, a result contradicting reports of a possible direct effect of Si as a fertilizer. In contrast, inoculation of plants, treated or not with Si, altered the expression of a set of nearly 4,000 genes. After functional categorization, many of the up-regulated genes were defense-related, whereas a large proportion of down-regulated genes were involved in primary metabolism. Regulated defense genes included R genes, stress-related transcription factors, genes involved in signal transduction, the biosynthesis of stress hormones (SA, JA, ethylene), and the metabolism of reactive oxygen species. In inoculated plants treated with Si, the magnitude of down-regulation was attenuated by >25%, an indication of stress alleviation. Our results demonstrate that Si treatment had no effect on the metabolism of unstressed plants, suggesting a nonessential role for the element but that it has beneficial properties attributable to modulation of a more efficient response to pathogen stress.

International audience; Barley yellow dwarf disease (BYDD) is one of the main viral diseases of small grain cereals. This disease, reported on numerous plant species of the Poaceae family, is caused by a complex of viral species including the species Barley yellow dwarf virus-PAV (BYDV-PAV, family Luteoviridae, genus Luteovirus), frequently found in western Europe. Resistance sources towards BYDD are scarce. Indeed, breeding-resistant genotypes is a long and expensive process. Thus, estimating the durability of the resistance genes before the achievement of selection would be an asset for breeders. One isolate of BYDV-PAV has been serially passaged on two hosts, 'Zhong ZH' and 'TC14', carrying a gene for partial resistance. The resulting viral population showed an increase of the speed of development of the infection in controlled conditions. In this study, these viral populations were evaluated in a 3-year field trial, including a susceptible host, 'Rendezvous', and a host carrying the resistance gene of 'TC14' in a 'Rendezvous' background, to assess the effect of serial passages in field conditions. Results indicate that isolates issued from serial passages on hosts carrying a gene for partial resistance induced increased damage in field conditions when compared with the initial isolate. Yield losses are mainly due to a decrease of the number of kernels per square metre. The interest on using partial resistance gene to control BYDD is discusse

Introduction et but de l’etude Les nanoparticules de dioxyde de titane (TiO2) sont largement utilisees comme additif alimentaire [1]. Toutefois, leur devenir dans l’intestin reste peu etudie [2]. L’objectif de l’etude est de caracteriser in vitro leurs interactions avec le mucus (fonction barriere) et les bacteries, representatives du microbiote intestinal ou retrouvees dans l’alimentation (effets antibacteriens). Materiel et methodes Les deux types de TiO2 utilises sont le P25 Aeroxide (reference) et le E171 (colorant alimentaire) sous deux formes metrologiques differentes (soniquee et non soniquee). Les particules ont ete caracterisees en termes de taille, charge de surface et fluorescence. La secretion de mucus par les cellules HT29-MTX a ete estimee par coloration des mucines au Bleu Alcian et par immunofluorescence sur MUC5AC. La migration des particules de TiO2 a ete suivie par imagerie de fluorescence dynamique en microscopie confocale. Les effets du TiO2 sur la croissance de bacteries, commensales (Escherichia coli, Lactobacillus rhamnosus GG) ou apportees par l’alimentation (Lactococcus lactis, Streptococcus thermophilus, Lactobacillus sakei), ont ete evalues sur culture pure en milieu conventionnel. La capacite de piegeage du TiO2 par les bacteries a ete determinee en imagerie de fluorescence UV au Synchrotron Soleil sur la ligne de lumiere DISCO. Resultats et Analyse statistique La caracterisation en taille de TiO2 P25 et E171 a mis en evidence la polydispersite initiale des suspensions avec la co-existence d’une population micronique, formee de gros agregats, et d’une population submicronique qui, apres sonication, devient predominante. En termes de charge de surface, les types P25 et E171 different essentiellement par leur point isoelectrique. La migration du TiO2 au sein du mucus a ete evaluee in situ, en temps reel et sans marquage prealable des particules grâce a leur fluorescence naturelle. Il a ete demontre que le TiO2 n’est pas au contact direct des cellules mais se localise preferentiellement dans des zones discretes de quelques μm d’epaisseur, vraisemblablement en lien avec la structure en ilots du mucus. Le suivi de la croissance bacterienne en presence de TiO2 a revele des effets deleteres sur l’ensemble des bacteries testees, i.e. augmentation du temps de latence et diminution du taux de croissance et de la biomasse finale par rapport aux conditions controle. Le colorant E171 semble avoir plus d’effet que le P25, surtout sous sa forme soniquee. La co-localisation bacteries/TiO2 a ete mise en evidence a l’echelle de la bacterie unique, par imagerie de fluorescence en rayonnement Synchrotron. Conclusion Le mucus joue un role de barriere vis-a-vis du TiO2 sous forme nanoparticulaire. Ces memes nanoparticules exercent des effets deleteres sur la croissance de certaines bacteries du microbiote, commensales ou alimentaires. Les avancees de ce travail permettront une meilleure evaluation des consequences d’une exposition au TiO2 par l’alimentation sur la sante humaine, en conditions physiologiques puis physiopathologiques ou le couple microbiote/mucus est altere (dysbiose bacterienne, fonction barriere du mucus fragilisee).

The yeast-like epiphytic fungus Pseudozyma flocculosa is known to antagonize powdery mildew fungi through proliferation on colonies presumably preceded by the release of an antifungal glycolipid (flocculosin). In culture conditions, P. flocculosa can be induced to produce or not flocculosin through manipulation of the culture medium nutrients. In order to characterize and understand the metabolic changes in P. flocculosa linked to glycolipid production, we conducted a 2-DE proteomic analysis and compared the proteomic profile of P. flocculosa growing under conditions favoring the development of the fungus (control) or conducive to flocculosin synthesis (stress). A large number of protein spots (771) were detected in protein extracts of the control treatment compared to only 435 matched protein spots in extracts of the stress cultures, which clearly suggests an important metabolic reorganization in slow-growing cells producing flocculosin. From the latter treatment, we were able to identify 21 protein spots that were either specific to the treatment or up-regulated significantly (2-fold increase). All of them were identified based on similarity between predicted ORF of the newly sequenced genome of P. flocculosa with Ustilago maydis' available annotated sequences. These proteins were associated with the carbon and fatty acid metabolism, and also with the filamentous change of the fungus leading to flocculosin production. This first look into the proteome of P. flocculosa suggests that flocculosin synthesis is elicited in response to specific stress or limiting conditions.