Cyanide Production by Rhizobacteria and Potential for Suppression of Weed Seedling Growth

Rhizobacteria strains were characterized for ability to synthesize hydrogen cyanide and for effects on seedling root growth of various plants. Approximately 32% of bacteria from a collection of over 2000 isolates were cyanogenic, evolving HCN from trace concentrations to >30 nmoles/mg cellular protein. Cyanogenesis was predominantly associated with pseudomonads and was enhanced when glycine was provided in the culture medium. Concentrations of HCN produced by rhizobacteria were similar to exogenous concentrations inhibiting seedling growth in bioassays, suggesting that cyanogenesis by rhizobacteria in the rhizosphere can adversely affect plant growth. Growth inhibition of lettuce and barnyardgrass by volatile metabolites of the cyanogenic rhizobacteria confirmed that HCN was the major inhibitory compound produced. Our results suggest that HCN produced in the rhizospheres of seedlings by selected rhizobacteria is a potential and environmentally compatible mechanism for biological control of weeds. Received: 13 December 2000/Accepted: 6 February 2001     

Essential oil composition of Hypericum triquetrifolium Turra. aerial parts

The essential oil obtained by hydrodistillation from the aerial parts of Tunisian endemic Hypericum triquetrifolium Turra (Clusiaceae) was analyzed using GC and GC-MS. One hundred and nine compounds consisting of 92.2% of total detected constituents were identified. Sesquiterpene hydrocarbons were the main constituents (59.37%), Alpha-humulene, cis-calamenene, delta-cadinene, bicyclogermacrene, eremophilene, betacaryophyllene and (E)-gamma-bisabolene were found as the main ones. Alpha-pinene (10.33%) was detected as the main monoterpene hydrocarbons (12.19%). The oxygenated sesquiterpenes constituted (9.33%); caryophyllene oxide (1.38%) was reported as the main constituent of this fraction. The oxygenated monoterpenes were weakly represented (4.62%) and consisted of constituents in low percentages (<1%).     

Biosynthesis of compatible solutes in rhizobial strains isolated from <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> nodules in Tunisian fields

Background  

Associated with appropriate crop and soil management, inoculation of legumes with microbial biofertilizers can improve food legume yield and soil fertility and reduce pollution by inorganic fertilizers. Rhizospheric bacteria are subjected to osmotic stress imposed by drought and/or NaCl, two abiotic constraints frequently found in semi-arid lands. Osmostress response in bacteria involves the accumulation of small organic compounds called compatible solutes. Whereas most studies on rhizobial osmoadaptation have focussed on the model species Sinorhizobium meliloti, little is known on the osmoadaptive mechanisms used by native rhizobia, which are good sources of inoculants. In this work, we investigated the synthesis and accumulations of compatible solutes by four rhizobial strains isolated from root nodules of Phaseolus vulgaris in Tunisia, as well as by the reference strain Rhizobium tropici CIAT 899^T.     

Biological control of great brome (<Emphasis Type="Italic">Bromus diandrus</Emphasis>) in durum wheat (<Emphasis Type="Italic">Triticum durum</Emphasis>): specificity,physiological traits and impact on plant growth and root architecture of the fluorescent pseudomonad strain X33d

The rhizobacterial strain X33d was previously shown to suppress the growth of the weed great brome (Bromus diandrus Roth.). The aim of this work was to identify X33d, characterize its physiological activities, assess its specificity on different non-target crops, and its impact on the growth and the root architecture of great brome and durum wheat (Triticum durum Desf.) grown alone and together. Based on 16S rDNA sequencing, X33d was identified as Pseudomonas trivialis. The specificity assay, performed on a mixture of soil/sand/peat, highlighted the suppressive activity of P. trivialis X33d against great brome and the promoting effect on most of the considered crops, especially durum wheat. Although the growth of durum wheat on quartz sand was unaffected, P. trivialis X33d suppressed the growth and affected the root architecture of great brome, especially when co-seeded with durum wheat. Great brome plants inoculated with X33d and co-seeded with durum wheat showed low root biomass, short root systems and low surface area, volume and number of tips. Moreover, P. trivialis X33d synthesized indole-acetic acid (IAA) that could be involved both in great brome growth suppression and durum wheat growth promotion. Our results indicate that P. trivialis X33d could be exploited as a potential biocontrol agent against great brome without affecting the durum wheat growth. These results are discussed in relation to the competitive capability of great brome towards durum wheat.     

A case of Kearns–Sayre syndrome with two novel deletions (9.768 and 7.253 kb) of the mtDNA associated with the common deletion in blood leukocytes,buccal mucosa and hair follicles

Kearns–Sayre syndrome is a mitochondrial disorder characterized by the emergence before the age of 20 years of progressive external ophthalmoplegia, pigmentary retinopathy, with other heterogeneous clinical manifestations. Generally, mitochondrial DNA deletions were associated with KSS but the size and position of these deletions differ among patients. This study reported a Tunisian patient with typical features of KSS. Long-range PCR amplification of the mtDNA in different tissues from this patient showed multiple mitochondrial deletions: two novel 9.768 and 7.253 kb deletions spanning respectively nucleotides 6124–15,893 and 8572–15,826 associated with the common 4.977 kb deletion.     

Contribution of PTPN22, CD28, CTLA-4 and ZAP-70 variants to the risk of type 1 diabetes in Tunisians

Type 1 diabetes (T1D) is caused by an immune-mediated destruction of the insulin-producing β-cells. Several studies support the involvement of T cell activation molecules. In order to underline the role of the genes involved in this pathway, we investigated, using the Sequenom MassARRAY platform, polymorphisms of sixteen single-nucleotide polymorphisms (SNPs) belonging to PTPN22, CD28, CTLA-4, and ZAP-70 genes in 76 T1D patients and 162 unrelated healthy controls from Southern Tunisia.     

Human cellular immune response to the saliva of Phlebotomus papatasi is mediated by IL-10-producing CD8+ T cells and Th1-polarized CD4+ lymphocytes

Background

The saliva of sand flies strongly enhances the infectivity of Leishmania in mice. Additionally, pre-exposure to saliva can protect mice from disease progression probably through the induction of a cellular immune response.

Methodology/Principal Findings

We analysed the cellular immune response against the saliva of Phlebotomus papatasi in humans and defined the phenotypic characteristics and cytokine production pattern of specific lymphocytes by flow cytometry. Additionally, proliferation and IFN-γ production of activated cells were analysed in magnetically separated CD4+ and CD8+ T cells. A proliferative response of peripheral blood mononuclear cells against the saliva of Phlebotomus papatasi was demonstrated in nearly 30% of naturally exposed individuals. Salivary extracts did not induce any secretion of IFN-γ but triggered the production of IL-10 primarily by CD8+ lymphocytes. In magnetically separated lymphocytes, the saliva induced the proliferation of both CD4+ and CD8+ T cells which was further enhanced after IL-10 blockage. Interestingly, when activated CD4+ lymphocytes were separated from CD8+ cells, they produced high amounts of IFN-γ.

Conclusion

Herein, we demonstrated that the overall effect of Phlebotomus papatasi saliva was dominated by the activation of IL-10-producing CD8+ cells suggesting a possible detrimental effect of pre-exposure to saliva on human leishmaniasis outcome. However, the activation of Th1 lymphocytes by the saliva provides the rationale to better define the nature of the salivary antigens that could be used for vaccine development.     

Biocontrol of broomrape (Orobanche crenata Forsk. and Orobanche foetida Poir. ) by Pseudomonas fluorescens isolate Bf7-9 from the faba bean rhizosphere

Bacteria of the faba bean (Vicia faba L.)/Orobanche spp. root environment were evaluated for their potential use as biocontrol agents for the parasitic weed. Bacteria were isolated mainly from the rhizosphere of faba bean as well as from diseased Orobanche underground structures and an Orobanche-suppressive soil from three districts of northern Tunisia. Out of 351 bacterial isolates, 337 were tested for pathogenicity in an inverted pyramidal-shape screening programme including a Lactuca sativa L. seedlings bioassay, root-chamber and pot experiments. In pre-selection screening on L. sativa seedlings, 37 isolates (11%) showed a strong growth inhibitory effect, of which 70 and 84% also had a significant suppressive activity on the pre-emergence structures of O. foetida and O. crenata, respectively, in root-chamber experiments. Among five bacterial isolates selected for pot trials, strain Bf7-9 of Pseudomonas fluorescens showed high biocontrol activity against both species of Orobanche and positively influenced faba bean growth. The bacterium reduced shoot emergence of O. crenata and O. foetida by 64 and 76% and their dry weight by 39 and 63%, respectively, compared with non-inoculated controls. Pseudomonas marginalis strain Nc1-2 exhibited also a tendency to reduce incidence of O. crenata and to improve faba bean performance. Results of the present study suggest that application of naturally occurring rhizosphere bacteria offers an additional approach for biocontrol of Orobanche spp. that can supplement current methods of control in an integrated weed management strategy.     

Antifungal mechanism of the combination of Cinnamomum verum and Pelargonium graveolens essential oils with fluconazole against pathogenic Candida strains

The present study aimed to investigate the anti-Candida activity of ten essential oils (EOs) and to evaluate their potential synergism with conventional drugs. The effect on secreted aspartic protease (SAP) activity and the mechanism of action were also explored. The antifungal properties of essential oils were investigated using standard micro-broth dilution assay. Only Cinnamomum verum, Thymus capitatus, Syzygium aromaticum, and Pelargonium graveolens exhibited a broad spectrum of activity against a variety of pathogenic Candida strains. Chemical composition of active essential oils was performed by gas chromatography-mass spectrometry (GC-MS). Synergistic effect was observed with the combinations C. verum/fluconazole and P. graveolens/fluconazole, with FIC value 0.37. Investigation of the mechanism of action revealed that C. verum EO reduced the quantity of ergosterol to 83%. A total inhibition was observed for the combination C. verum/fluconazole. However, P. graveolens EO may disturb the permeability barrier of the fungal cell wall. An increase of MIC values of P. graveolens EO and the combination with fluconazole was observed with osmoprotectants (sorbitol and PEG6000). Furthermore, the combination with fluconazole may affect ergosterol biosynthesis and disturb fatty acid homeostasis in C. albicans cells as the quantity of ergosterol and oleic acid was reduced to 52.33 and 72%, respectively. The combination of P. graveolens and C. verum EOs with fluconazole inhibited 78.31 and 64.72% SAP activity, respectively. To our knowledge, this is the first report underlying the mechanism of action and the inhibitory effect of SAP activity of essential oils in synergy with fluconazole. Naturally occurring phytochemicals C. verum and P. graveolens could be effective candidate to enhance the efficacy of fluconazole-based therapy of C. albicans infections.     

Prediction of T Cell Epitopes from Leishmania major Potentially Excreted/Secreted Proteins Inducing Granzyme B Production

Leishmania-specific cytotoxic T cell response is part of the acquired immune response developed against the parasite and contributes to resistance to reinfection. Herein, we have used an immune-informatic approach for the identification, among Leishmania major potentially excreted/secreted proteins previously described, those generating peptides that could be targeted by the cytotoxic immune response. Seventy-eight nonameric peptides that are predicted to be loaded by HLA-A*0201 molecule were generated and their binding capacity to HLA-A2 was evaluated. These peptides were grouped into 20 pools and their immunogenicity was evaluated by in vitro stimulation of peripheral blood mononuclear cells from HLA-A2⁺-immune individuals with a history of zoonotic cutaneous leishmaniasis. Six peptides were identified according to their ability to elicit production of granzyme B. Furthermore, among these peptides 3 showed highest affinity to HLA-A*0201, one derived from an elongation factor 1-alpha and two from an unknown protein. These proteins could constitute potential vaccine candidates against leishmaniasis.