Xylella fastidiosa is a fastidious, xylem-limited bacterium that causes a range of economically important plant diseases. Here we report the complete genome sequence of X. fastidiosa clone 9a5c, which causes citrus variegated chlorosis--a serious disease of orange trees. The genome comprises a 52.7% GC-rich 2,679,305-base-pair (bp) circular chromosome and two plasmids of 51,158 bp and 1,285 bp. We can assign putative functions to 47% of the 2,904 predicted coding regions. Efficient metabolic functions are predicted, with sugars as the principal energy and carbon source, supporting existence in the nutrient-poor xylem sap. The mechanisms associated with pathogenicity and virulence involve toxins, antibiotics and ion sequestration systems, as well as bacterium-bacterium and bacterium-host interactions mediated by a range of proteins. Orthologues of some of these proteins have only been identified in animal and human pathogens; their presence in X. fastidiosa indicates that the molecular basis for bacterial pathogenicity is both conserved and independent of host. At least 83 genes are bacteriophage-derived and include virulence-associated genes from other bacteria, providing direct evidence of phage-mediated horizontal gene transfer.
Xylella fastidiosa is a xylem-dwelling, insect-transmitted, gamma-proteobacterium that causes diseases in many plants, including grapevine, citrus, periwinkle, almond, oleander, and coffee. X. fastidiosa has an unusually broad host range, has an extensive geographical distribution throughout the American continent, and induces diverse disease phenotypes. Previous molecular analyses indicated three distinct groups of X. fastidiosa isolates that were expected to be genetically divergent. Here we report the genome sequence of X. fastidiosa (Temecula strain), isolated from a naturally infected grapevine with Pierce's disease (PD) in a wine-grapegrowing region of California. Comparative analyses with a previously sequenced X. fastidiosa strain responsible for citrus variegated chlorosis (CVC) revealed that 98% of the PD X. fastidiosa Temecula genes are shared with the CVC X. fastidiosa strain 9a5c genes. Furthermore, the average amino acid identity of the open reading frames in the strains is 95.7%. Genomic differences are limited to phage-associated chromosomal rearrangements and deletions that also account for the strain-specific genes present in each genome. Genomic islands, one in each genome, were identified, and their presence in other X. fastidiosa strains was analyzed. We conclude that these two organisms have identical metabolic functions and are likely to use a common set of genes in plant colonization and pathogenesis, permitting convergence of functional genomic strategies.Different microorganisms are able to survive in and to colonize plant water-conductive vessels (xylem). The result of this association is either beneficial or detrimental to the plant host.Of the latter, an example is the association of Xylella fastidiosa (38) with diverse plant hosts. X. fastidiosa is a fastidious, insecttransmitted, xylem-inhabiting bacterium known to cause several economically important diseases of both monocotyledonous and dicotyledonous plants (14,17,29). These diseases include Pierce's disease (PD) of grapevine and citrus variegated chlorosis (CVC), which have rather distinct symptoms and geographical distributions.PD, caused by certain strains of X. fastidiosa, is characterized by wilted, shriveled, raisin-like fruit and scorched leaves that detach, leaving bare petioles attached to the canes (37). The bark of affected canes may lignify or mature irregularly, leaving
To identify differentially expressed genes in soybean grown under different drought conditions, cDNA libraries from roots of different genotypes were constructed. Genes of contrasting genotypes of soybean were found to be differentially expressed in plants exposed to drought conditions. A total of 753 no redundant clones were identified by PCR, and these were printed on microarray glass slides. Probes of total RNA were prepared from bulked roots subjected to 25 and 50 min (Bulk 1) or 75 and 100 min (Bulk 2) of drought stress. Differential expression of 145 genes, involved in metabolic pathways responsive to biotic and abiotic stresses, was observed. These genes were classified into nine functional categories, including energy, transcription factors, metabolism, stress response, protein synthesis, cell communication, cell cycle, cell transport, and unknown function. The functionality of some of these genes was confirmed by quantitative real-time PCR (qRT-PCR).
Until recently, few studies were carried out in Brazil about diversity of bacterial soil communities. Aiming to characterize the bacterial population in the soil through 16S rRNA analysis, two types of soil have been analyzed: one of them characterized by intensive use where tomato, beans and corn were cultivated (CS); the other analyzed soil was under forest (FS), unchanged by man; both located in Guaíra, São Paulo State, Brazil. Using specific primers, 16S rRNA genes from metagenomic DNA in both soils were amplified by PCR, amplicons were cloned and 139 clones from two libraries were partially sequenced. The use of 16S rRNA analysis allowed identification of several bacterial populations in the soil belonging to the following phyla: Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria Verrucomicrobia in addition to the others that were not classified, beyond Archaea domain. Differences between FS and CS libraries were observed in size phyla. A larger number of phyla and, consequently, a greater bacterial diversity were found in the under-forest soil. These data were confirmed by the analyses of genetic diversity that have been carried out. The characterization of bacterial communities of soil has made its contribution by providing facts for further studies on the dynamics of bacterial populations in different soil conditions in Brazil.
The role of cell wall polysaccharides in leucocyte recruitment and granuloma formation in paracoccidioidomycosis was investigated. The inflammatory cells recruitment to the peritoneal cavity in rats inoculated with cell wall fraction (CW-265 or F1-265) from an avirulent strain of Paracoccidioides brasiliensis (Pb265), was greater than that observed for the cell wall fraction (CW-HC or F1-HC) recovered from the virulent strain (PbHC). Moreover, the inoculation of F1-HC and F1-265 into the subcutaneous layer of mice resulted in the formation of nodular and not progressive granulomatous lesions. The size and mean time of evolution of these lesions was proportional to the degree of virulence of the sample from which they were derived. Analyses showed that both F1 fractions contained P-glucan and chitin. Only P-glucan was able to trigger attraction and concentric organization of polymorphonuclear neutrophils and macrophages at the inflammatory foci, and the difference in the concentration of this compound in the cell walls of PbHC and Pb265 could explain the inflammatory capacity exhibited by the two strains of P. brasiliensis.
Studies on the impact of Eucalyptus spp. on Brazilian soils have focused on soil chemical properties and isolating interesting microbial organisms. Few studies have focused on microbial diversity and ecology in Brazil due to limited coverage of traditional cultivation and isolation methods. Molecular microbial ecology methods based on PCR amplified 16S rDNA have enriched the knowledge of soils microbial biodiversity. The objective of this work was to compare and estimate the bacterial diversity of sympatric communities within soils from two areas, a native forest (NFA) and an eucalyptus arboretum (EAA). PCR primers, whose target soil metagenomic 16S rDNA were used to amplify soil DNA, were cloned using pGEM-T and sequenced to determine bacterial diversity. From the NFA soil 134 clones were analyzed, while 116 clones were analyzed from the EAA soil samples. The sequences were compared with those online at the GenBank. Phylogenetic analyses revealed differences between the soil types and high diversity in both communities. Soil from the Eucalyptus spp. arboretum was found to have a greater bacterial diversity than the soil investigated from the native forest area.
SUMMARYTumour neerosis factor (TNF) was detected in serum from miee challenged with Paraeoccidioides hra.silien.sls. The serum TNF' levels of miee challenged with an aviruicnt strain were significantly higher than those of mice challenged with a virulent strain, and the same was observed for the TNF levels of mice challenged with a cell wall fraction (Fl) from the two fungal strains. Fraction Fl eonsistedofehitin and /y-g!uean; bul although thcchitincontents were similar for the two strains, the aviruicnt strain allowed a greater content of/f-glucan. The /(-glucan, purified from both strains, inereased serum TNF levels in an identical dosc-dcpcndent manner, whereas purified ehitin did not induee serum TNF levels. P. brasiliensis. the Fl fractions and ^-glucan induced maerophages to seerete TNF in vitro. The differences in TNF levels, induced by the difTerent fungal strains, were correlated wilh the/f-gluean concentrations in the cell walls of both iheavirulent and virulent strains of P. hra.sitien.sis. These findings support a role for TNF in the palhogenieity of P. brasiliensis.
Microbial communities drive biogeochemical cycles in agricultural areas by decomposing organic materials and converting essential nutrients. Organic amendments improve soil quality by increasing the load of essential nutrients and enhancing the productivity. Additionally, fresh water used for irrigation can affect soil quality of agricultural soils, mainly due to the presence of microbial contaminants and pathogens. In this study, we investigated how microbial communities in irrigation water might contribute to the microbial diversity and function of soil. Whole-metagenomic sequencing approaches were used to investigate the taxonomic and the functional profiles of microbial communities present in fresh water used for irrigation, and in soil from a vegetable crop, which received fertilization with organic compost made from animal carcasses. The taxonomic analysis revealed that the most abundant genera were Polynucleobacter (~8% relative abundance) and Bacillus (~10%) in fresh water and soil from the vegetable crop, respectively. Low abundance (0.38%) of cyanobacterial groups were identified. Based on functional gene prediction, denitrification appears to be an important process in the soil community analysed here. Conversely, genes for nitrogen fixation were abundant in freshwater, indicating that the N-fixation plays a crucial role in this particular ecosystem. Moreover, pathogenicity islands, antibiotic resistance and potential virulence related genes were identified in both samples, but no toxigenic genes were detected. This study provides a better understanding of the community structure of an area under strong agricultural activity with regular irrigation and fertilization with an organic compost made from animal carcasses. Additionally, the use of a metagenomic approach to investigate fresh water quality proved to be a relevant method to evaluate its use in an agricultural ecosystem.
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