The microbiome of xylem sap associated with almond leaf scorch disease caused by Xylella fastidiosa in South East Spain

Xylella fastidiosa (XF) is one of the most harmful emerging plant pathogenic bacteria and represents an important threat to agriculture, forestry and landscape worldwide. In June of 2017 XF was reported in almond trees in the province of Alicante, Spain. Metagenomics is a valuable methodology to study the impact of causal agents of plant diseases and their interaction with others naturally occurring microorganism, as part of innovative approaches to mitigate or control the disease. Moreover, endophytic bacteria seem to be a promising biocontrol solution. The objective of the study was to compare healthy and diseased almonds trees infected by XF subsp. multiplex to identify groups of microorganisms that could potentially modulate the almond leaf scorch disease. Almond plots were selected in five municipalities within the demarcated area of XF outbreak. A total of 93 trees were selected and characterized as positive (52) and negative (41) for the presence of XF using official EPPO standard qPCR protocols. The bacterial microbiota was determined from DNA extracted from xylem samples of wood chips based on the V5-V6 region of the bacterial 16S rRNA gene using Illumina’s MiSeq sequencing. There was a clear concordance between qPCR results and identification of XF reads in the samples. Within the diseased plants, the relative abundance of XF varied from 0.34% to 92% of total bacterial reads. In total, 152 OTUs were assigned to 11 phyla, 53 families and 86 genera. A core microbiome of 77 OTUs common to healthy (qPCR negative) and diseased (qPCR positive) almond trees was determined were 5 genera accounted for most of the diversity. Disruption in the frequencies of these OTUs occurred on the diseased tree since those predominant genera were less abundant due to the emergence of Xylella. Furthermore, 32 and 38 OTUs were unique to healthy or diseased trees, respectively. Our results allow to better understand the interaction between XF and the xylem sap microbiome identifying potential bacteria that could act through direct inhibition or through niche displacement of XF envisioning innovative strategies to control the almond leaf scorch disease.Study supported by Project 727987 XF ACTORS(EU-H2020) and COST Action CA16107 EuroXanth

Spin reorientation and crystal-field interaction in TbFe 12Àx Ti x single crystals

The magnetic properties of TbFe 12Ϫx Ti x single crystals with xϭ0.8-1.4 have been investigated in detail using ac and dc susceptibility and high-field magnetization measurements. A first-order spin reorientation transition from a basal plane easy magnetization direction at low temperatures to an axial easy magnetization direction at high temperatures occurs for all the investigated compounds. The spin reorientation temperatures have been determined by combining ac and dc susceptibility measurements and its dependence on both the Ti content and the applied magnetic field has been studied. A first-order magnetization process is observed below a certain temperature when the magnetic field is applied along the ͓001͔ crystallographic direction. The dependence of the transition critical field on the Ti content has been analyzed. The magnetic behavior has been interpreted using a two-sublattices model for the magnetic structure, in the frame of a crystal-electric-fieldmean-field model. The parameters describing the crystal-field interaction in TbFe 12Ϫx Ti x compounds have been determined. The calculated magnetic behavior shows a good agreement with experimental results in a wide temperature range

Epitaxy and magnetotransport of Sr_2FeMoO_6 thin films

By pulsed-laser deposition epitaxial thin films of Sr_2FeMoO_6 have been pre- pared on (100) SrTiO_3 substrates. Already for a deposition temperature of 320 C epitaxial growth is achieved. Depending on deposition parameters the films show metallic or semiconducting behavior. At high (low) deposition temperature the Fe,Mo sublattice has a rock-salt (random) structure. The metallic samples have a large negative magnetoresistance which peaks at the Curie temperature. The magnetic moment was determined to 4 mu_B per formula unit (f.u.), in agreement with the expected value for an ideal ferrimagnetic arrangement. We found an ordinary Hall coefficient of -6.01x10^{-10} m^3/As at 300 K, corresponding to an electronlike charge-carrier density of 1.3 per Fe,Mo-pair. In the semiconducting films the magnetic moment is reduced to 1 mu_B/f.u. due to disorder in the Fe,Mo sublattice. In low fields an anomalous holelike contribution dominates the Hall voltage, which vanishes at low temperatures for the metallic films only.Comment: Institute of Physics, University of Mainz, Germany, 4 pages, including 5 pictures and 1 Table, submitted to Phys. Rev.

Effective three-band model for double perovskites

We start from a six-band model describing the transition-metal t2g orbitals of half-metallic double perovskite systems, such as Sr2FeMoO6, in which only one of the transition metal ions (Fe) contains important intratomic repulsion Ufe. By eliminating the Mo orbitals using a low-energy reduction similar to that used in the cuprates, we construct a Hamiltonian which contains only effective t2g Fe orbitals. This allows to treat exactly Ufe, and most of the Fe-Mo hopping. As an application, we treat the effective Hamiltonian in the slave-boson mean-field approximation and calculate the position of the metal-insulator transition and other quantities as a function of pressure or on-site energy difference.Comment: 8 pages, 3 figure

Discontinuous transitions in double exchange materials

It is shown that the double exchange Hamiltonian, with weak antiferromagnetic interactions, has a rich variety of first order transitions between phases with different electronic densities and/or magnetizations. For band fillings in the range $0.3 \le x \le 0.5$, and at finite temperatures, a discontinuous transition between phases with similar electronic densities but different magnetizations takes place. This sharp transition, which is not suppressed by electrostatic effects, and survives in the presence of an applied field, is consistent with the phenomenology of the doped manganites near the transition temperature.Comment: three more variational ansatzs considere

On the origin of neutron magnetic scattering in anti-site disordered Sr2FeMoO6 double perovskites

Anti-site disordering in Sr2FeMoO6 double perovskites (containing Mo atoms at Fe positions, and viceversa) has recently been shown to have a dramatic influence in their magnetic and magnetotransport properties. In the present study, two polycrystalline Sr2FeMoO6 samples showing different degrees of anti-site disorder (a nominally 'ordered' sample with 70% of cationic ordering and a nominally 'disordered' sample with 18% of cationic ordering) have been examined by magnetic measurements and neutron powder diffraction (NPD) techniques in the 15-500K temperature range. Our main finding is that the 'disordered' sample exhibits a strong magnetic scattering (noticeable even at 500K), comparable to that displayed by the 'ordered' one below TC= 415 K. For the 'disordered' sample, the magnetic scattering exhibited on low angle Bragg positions, is not to be ascribed to a (non-existent) ferrimagnetic ordering: our results suggest that it originates upon naturally-occurring groups of Fe cations in which strong antiferromagnetic (AFM) Fe-O-Fe superexchange interactions are promoted, similar to those existing in the LaFeO3 perovskite. These Fe groups are not magnetically isolated, but coupled by virtue of Fe-O-Mo AFM interactions, which maintain the long-range coherence of this AFM structure. Susceptibility measurements confirm the presence of AFM interactions below 770 K.Comment: 30 pages, 11 figures, to be published in PR

Non-L\'evy mobility patterns of Mexican Me'Phaa peasants searching for fuelwood

We measured mobility patterns that describe walking trajectories of individual Me'Phaa peasants searching and collecting fuelwood in the forests of "La Monta\~na de Guerrero" in Mexico. These one-day excursions typically follow a mixed pattern of nearly-constant steps when individuals displace from their homes towards potential collecting sites and a mixed pattern of steps of different lengths when actually searching for fallen wood in the forest. Displacements in the searching phase seem not to be compatible with L\'evy flights described by power-laws with optimal scaling exponents. These findings however can be interpreted in the light of deterministic searching on heavily degraded landscapes where the interaction of the individuals with their scarce environment produces alternative searching strategies than the expected L\'evy flights. These results have important implications for future management and restoration of degraded forests and the improvement of the ecological services they may provide to their inhabitants.Comment: 15 pages, 4 figures. First version submitted to Human Ecology. The final publication will be available at http://www.springerlink.co

LAL Regulators SCO0877 and SCO7173 as Pleiotropic Modulators of Phosphate Starvation Response and Actinorhodin Biosynthesis in Streptomyces coelicolor

LAL regulators (Large ATP-binding regulators of the LuxR family) constitute a poorly studied family of transcriptional regulators. Several regulators of this class have been identified in antibiotic and other secondary metabolite gene clusters from actinomycetes, thus they have been considered pathway-specific regulators. In this study we have obtained two disruption mutants of LAL genes from S. coelicolor (Δ0877 and Δ7173). Both mutants were deficient in the production of the polyketide antibiotic actinorhodin, and antibiotic production was restored upon gene complementation of the mutants. The use of whole-genome DNA microarrays and quantitative PCRs enabled the analysis of the transcriptome of both mutants in comparison with the wild type. Our results indicate that the LAL regulators under study act globally affecting various cellular processes, and amongst them the phosphate starvation response and the biosynthesis of the blue-pigmented antibiotic actinorhodin. Both regulators act as negative modulators of the expression of the two-component phoRP system and as positive regulators of actinorhodin biosynthesis. To our knowledge this is the first characterization of LAL regulators with wide implications in Streptomyces metabolism

Verbal fluency tests: Normative data for Spanish-speaking pediatric population

OBJECTIVE: To generate normative data for the phonological and semantic verbal fluency tests (VFT) in Spanish-speaking pediatric populations. METHOD: The sample consisted of 4,373 healthy children from nine countries in Latin America (Chile, Cuba, Ecuador, Guatemala, Honduras, Mexico, Paraguay, Peru, and Puerto Rico) and Spain. Each participant was administered the VFT as part of a larger neuropsychological battery. Scores for letters F, A, S, and animals and fruit categories were normed using multiple linear regressions and standard deviations of residual values. Age, age2, sex, and mean level of parental education (MLPE) were included as predictors in the analyses. RESULTS: The final multiple linear regression models showed main effects for age on all scores, such that scores increased linearly as a function of age. Age2 had a significant effect in Chile (animals), Cuba (A letter, fruits), Ecuador (animals, fruits), Honduras (F letter), Mexico (animals, fruits), Peru (fruits), and Spain (S letters, animals, fruits). Models showed an effect for MLPE in Chile (A letters, animals, fruits), Ecuador (S letter, animals, fruits), Guatelama (F, S letter, animals), Honduras (animals), Mexico (F, A, S letters, animals, fruits), Puerto Rico (A, letters, animals), and Spain (all scores). Sex scores were found significant in Chile (animals), Ecuador (A letter, fruits), Mexico (F letter, fruits), Paraguay (F, A, S letters, fruits), Puerto Rico (F letter, animals, fruits), and Spain (F letter, fruits). CONCLUSIONS: This is the largest multi-national Spanish speaking-pediatric normative study in the world, and as such it will allow neuropsychologists from these countries to have a more accurate way to interpret the phonological and semantic VFT in pediatric populations