Mechanisms of plant protection against two oxalate-producing fungal pathogens by oxalotrophic strains of Stenotrophomonas spp.

Plant Molecular Biology - Oxalotrophic Stenotrophomonas isolated from tomato rhizosphere are able to protect plants against oxalate-producing pathogens by a combination of actions including...     

The use of systems analysis methods in the sustainable management of wetlands

The management of the utilisation of natural resources from wetland ecosystems is a multiobjective and complex task. The creation of innovative decision making tools for sustainable wetland resource utilisation is an important challenge for the future. This is particularly crucial in the light of the growing shortages for high quality freshwater and the vanishing habitat for a large number of wetland fauna and flora species. Because wetlands combine attributes of both aquatic and terrestrial ecosystems, wetlands are often at the crossroads of a number of disciplines with no specific discipline of its own. Therefore, management programmes require a multidisciplinary approach founded on a systematic monitoring of key biological and physical parameters. A European Commission DG XII research project dedicated to the development of management tools for wetland resources in Latin America is being developed by a multidisciplinary team of researchers from eight universities, located in four EU member states, Argentina and Brazil. The study sites that will be utilised for this analysis are two shallow lakes in Northeast Argentina within the large (13000 km²) wetland `Esteros del Ibera'. Continuous and periodic in-situ monitoring instrumentation has been installed in a long term monitoring programme of hydrological and meteorological factors, coupled with monthly biological and ecological data gathering. Potential future scenarios for wetland resource use are being discussed in a series of public meetings with key provincial and local actors (teachers, university professors, clergymen, local business persons and politicians). These meetings address both the small scale modifications of wetland use (water extraction for agriculture, tourism, controlled hunting) as well as regional projects related to the creation of large scale economic development (forestation, modification of nearby waterways for hydroelectric production and increased river transportation). Models are developed relating the chemical, physical, biological and ecological parameters monitored. These models will be dedicated to analysing the effects of development on wetland functions and resource quality. An economic model will be created to evaluate potential modifications in wetland functions in the local and regional socio-economic context. Evaluation instruments are developed and tested which include; qualitative models using loop analysis, goal functions based on the aquatic trophic web and the overall energy flux in the lagoon, and a geographical information system utilising satellite images. The purpose of these instruments is to examine the overall impacts of development alternatives on resource quality and ecosystem integrity, as well as demonstrating key parameters that should be more closely monitored. The final package will include an evaluation of the potential impacts of the development scenarios proposed by the key actors, recommendations to reduce specific impacts through alternative technologies, together with a monitoring programme and analysis tools for improved decision making in wetland resource management.     

Variations in the periphytic community structure and dynamics of Lake Nahuel Huapi (Patagonia,Argentina)

Little is known about periphyton community in Patagonia and the influence that urban development has on a particular water body. Lake Nahuel Huapi is located in a National Park with little industrial or agricultural activity in the basin, but it is influenced by urban discharges from San Carlos de Bariloche, a town of 80000 inhabitants located on its south shore. Variations in structure and dynamics of the periphyton community in Lake Nahuel Huapi were studied during 1 year, to examine the influence of urban discharges on this community. Periphyton samples were collected on the shoreline of the lake and evaluated for biomass (as chlorophyll a concentration) and cell density of the main algal groups, at sites with and without urban influence. Results indicated the major influence of pollution from urban sources on periphyton at the most impacted sites, as well as the effect of different local events at each site (degree of contamination, type of coast, wind exposure, etc.). Higher biomass and cell densities at contaminated sites were evident, but the variation of main algal groups through the year was similar in all the sites. Periphyton in Lake Nahuel Huapi proved to be an important bioindicator of urban impacts on this water body.     

Differences in nocturnal basal and rhythmic prolactin secretion in untreated compared to treated HIV-infected men are associated with CD4+ T-lymphocytes

The existence of decreased hypothalamic dopaminergic tone in HIV-infected men has been suggested. In a cross-sectional study, we determined 12 h nocturnal basal and pulsatile prolactin (PRL) release levels (by blood sampling every 10 min) and their correlation with CD4+ T cells in seven volunteer HIV-negative, healthy men (group 1), and 21 normoprolactinemic, euthyroid, HIV-infected men divided into 3 groups (each group = 7): (i) group 2, asymptomatic HIV-infected stage A1 men, untreated; (ii) group 3, AIDS stage C3 without active opportunistic infections, untreated; and (iii) group 4, previously stage C3 after at least 6 months of successful highly active antiretroviral therapy. Serum PRL was measured by radioimmunoanalysis and the results were analysed by waveform-independent deconvolution analysis. CD4+ T lymphocytes were measured by flow cytometry and viral load by a nucleic acid sequence-based amplification assay. No differences were detected in the first two groups. In the third group, however, 100% of prolactin secretion was found to be pulsatile with a shorter secretory burst duration (P = 0.04), and a greater circulating half-life and pulse amplitude (P < or = 0.04). Group 4 had the greatest basal prolactin secretion (P < or = 0.04), and a shorter secretory burst duration (P = 0.04 vs group 2), circulating half-life (P = 0.01 vs group 3) and intersecretory burst interval (P = 0.06 vs group 1). PRL approximate entropy was similar among all groups. Linear correlations existed between CD4+ T cell counts and PRL secretory burst half duration (r = 0.62, P = 0.002) and amplitude (r = -0.63, P = 0.001), and in circulating serum half-life (r = - 0.61, P = 0.002) in HIV-infected groups. Viral load showed no correlations. It is suggested that differential changes in nocturnal prolactin secretion among HIV-infected men occurred while maintaining the normal coordinate feedback and/or feedforward control within the lactotropic axis. These changes may represent an adaptative mechanism to sustain, by different means, the maximal physiologic PRL production to stimulate the highest cellular immune response and/or reconstitution in attempting to survive.     

The genome sequence of the gram-positive sugarcane pathogen Leifsonia xyli subsp. xyli

The genome sequence of Leifsonia xyli subsp. xyli, which causes ratoon stunting disease and affects sugarcane worldwide, was determined. The single circular chromosome of Leifsonia xyli subsp. xyli CTCB07 was 2.6 Mb in length with a GC content of 68% and 2,044 predicted open reading frames. The analysis also revealed 307 predicted pseudogenes, which is more than any bacterial plant pathogen sequenced to date. Many of these pseudogenes, if functional, would likely be involved in the degradation of plant heteropolysaccharides, uptake of free sugars, and synthesis of amino acids. Although L. xyli subsp. xyli has only been identified colonizing the xylem vessels of sugarcane, the numbers of predicted regulatory genes and sugar transporters are similar to those in free-living organisms. Some of the predicted pathogenicity genes appear to have been acquired by lateral transfer and include genes for cellulase, pectinase, wilt-inducing protein, lysozyme, and desaturase. The presence of the latter may contribute to stunting, since it is likely involved in the synthesis of abscisic acid, a hormone that arrests growth. Our findings are consistent with the nutritionally fastidious behavior exhibited by L. xyli subsp. xyli and suggest an ongoing adaptation to the restricted ecological niche it inhabits.     

Repression of the RcsC-YojN-RcsB phosphorelay by the IgaA protein is a requisite for Salmonella virulence

Bacterial pathogenesis relies on regulators that activate virulence genes. Some of them act, in addition, as repressors of specific genes. Intracellular-growth-attenuator-A (IgaA) is a Salmonella enterica membrane protein that prevents overactivation of the RcsC-YojN-RcsB regulatory system. This negative control is critical for growth because disruption of the igaA gene is only possible in rcsC, yojN or rcsB strains. In this work, we examined the contribution of this regulatory circuit to virulence. Viable igaA point mutant alleles were isolated and characterized. These alleles encode IgaA variants leading to different levels of activation of the RcsC-YojN-RcsB system. IgaA-mediated repression of the RcsB-YojN-RcsC system occurred at the post-translational level, as shown by chromosomal epitope tagging of the rcsC, yojN and rcsB genes. The activity of the RcsC-YojN-RcsB system, monitored with the product of a tagged gmd-3xFLAG gene (positively regulated by RcsC-YojN-RcsB), was totally abolished by wild-type bacteria in mouse target organs. Such tight repression occurred only in vivo and was mediated by IgaA. Shutdown of the RcsC-YojN-RcsB system is a requisite for Salmonella virulence since all igaA point mutant strains were highly attenuated. The degree of attenuation correlated to that of the activation status of RcsC-YojN-RcsB. In some cases, the attenuation recorded was unprecedented, with competitive index (CI) values as low as 10(-6). Strikingly, IgaA is a protein absolutely dispensable for virulence in mutant strains having a non-functional RcsC-YojN-RcsB system. To our knowledge, IgaA exemplifies the first protein that contributes to virulence by exclusively acting as a negative regulator upon host colonization.     

Activity of oil-formulated Beauveria bassiana against Triatoma sordida in peridomestic areas in Central Brazil

Field tests were carried out during the rainy season of 2001/2002 in S?o Luís de Montes Belos, Goiás, Brazil, to evaluate the potential of the entomopathogenic fungus, Beauveria bassiana, against peridomestic Triatoma sordida. An oil-water formulation of the isolate CG 14 (Embrapa) was applied in triatomine infested hen houses of four farms at a final concentration of 10(6) conidia/cm2. Numbers of T. sordida decreased over the next 25 days, after application of the fungus, and B. bassiana developed on dead insects in one hen house. A high number of B. bassiana colonies was detected in substrates collected in treated hen houses 24 h after application of CG 14. In the following three months the presence of B. bassiana declined to values found before treatment.     

Gamma carbonic anhydrase like complex interact with plant mitochondrial complex I

We report the identification by two hybrid screens of two novel similar proteins, called Arabidopsis thaliana gamma carbonic anhydrase like1 and 2 (AtCAL1 and AtCAL2), that interact specifically with putative Arabidopsis thaliana gamma Carbonic Anhydrase (AtCA) proteins in plant mitochondria. The interaction region that was located in the N-terminal 150 amino acids of mature AtCA and AtCA like proteins represents a new interaction domain. In vitro experiments indicate that these proteins are imported into mitochondria and are associated with mitochondrial complex I as AtCAs. All plant species analyzed contain both AtCA and AtCAL sequences indicating that these genes were conserved throughout plant evolution. Structural modeling of AtCAL sequences show a deviation of functionally important active site residues with respect to CAs but could form active interfaces in the interaction with AtCAs. We postulate a CA complex tightly associated to plant mitochondrial complex.