Efecto de los detritos aviarios en la diversidad y composición de las comunidades de microorganismos del suelo en el alcornocal de la Vera de Doñana (Huelva, España)

Motivación: En la Pajarera del Parque Nacional de Doñana miles de aves zancudas nidifican sobre alcornoques centenarios. Estudios recientes han relacionado las acumulación de guano con alteraciones de los parámetros químicos del suelo (aumento de la salinidad y del contenido nitratos y fosfatos) (1) y el decaimiento y muerte de los alcornoques. Se comprobó que los depósitos aviarios producen cambios en la abundancia de algunos oomicetos (2) como el patógeno Phytphthora cinnamomi, responsable de la podredumbre radical y muerte de distintas especies de plantas, incluida el alcornoque. El objetivo general del presente trabajo es estudiar el efecto de un gradiente natural de influencia aviaria en las comunidades microbianas del suelo y elucidar qué cambios edáficos explican mejor las alteraciones observadas en la composición y diversidad en tres grupos de microorganismos (arqueas, bacterias y hongos). Métodos: Se han caracterizado 63 micrositios usando la técnica de análisis de fragmentos terminales polimórficos de restricción (T-RFLP) (3), basada en la realización de una PCR usando cebadores marcados fluorescentemente para amplificar regiones ribosomales altamente conservadas (16S rADN para bacterias y arqueas y la región ITS entre los genes 18S y 28S rADN para hongos). Seguidamente se realizó una digestión y se midió la longitud de los fragmentos terminales mediante un secuenciador de ADN, resultando un perfil para cada grupo de microorganismos en el que cada pico se asimila a una única unidad taxonómica operacional (OTU). Resultados y conclusiones: La respuesta de la diversidad global (H' de Shannon) a los cambios en las variables ambientales es máxima en arqueas, creciendo con la salinidad y la eutrofización del medio, que promueven un incremento de equitatividad en las comunidades. En hongos y bacterias, la relación entre la diversidad y las variables ambientales medidas fue nula o muy débil (con el P). El análisis de redundancia canónica (RDA), mostró que las variables que mejor explican los cambios en la composición de las comunidades difieren entre los grupos: salinidad en arqueas; salinidad y P en bacterias y P, pH y humedad en hongos. Se concluye que los cambios edáficos derivados de las deposiciones aviarias afectan significativamente a la diversidad y estructura de las comunidades microbianas de los sitios afectados y de forma distinta a los tres grupos de microorganismos estudiados

A metabolic model inferred from a pangenome core predicts new biochemical functions for the phytopathogen 'Xylella fastidiosa'

Resumen del trabajo presentado al 44º Congreso de la Sociedad Española de Bioquímica y Biología Molecular, celebrado en Málaga del 6 al 9 de septiembre de 2022.Peer reviewe

Pathogenicity of Xylella fastidiosa subsp. multiplex isolates from Alicante outbreak (mainland Spain) on different hosts

In the outbreak of Xylella fastidiosa in the province of Alicante (mainland Spain), all isolates characterized so far belong to subsp. multiplex and ST6, and the main host is Prunus dulcis. Two different strains (IVIA 5901 and ESVL), isolated from almond trees in two municipalities of the Demarcated Area, were used to carry out pathogenicity tests on different plant species. The Italian strain De Donno (subsp. pauca, ST53) and the Spanish strain IVIA 5770 (subsp. fastidiosa, ST1) were also included

Patogenicidad de aislados de Xylella fastidiosa subsp. multiplex del foco de Alicante en diferentes hospedadores

Xylella fastidiosa es una de las principales bacterias de cuarentena en la Unión Europea, que habita en el xilema de la planta hospedadora y el tracto digestivo de insectos que actúan como vectores. Se multiplica en los vasos conductores de numerosas especies vegetales, pudiendo llegar a obstruir el flujo de savia, lo que provoca síntomas de estrés hídrico que pueden causar la muerte de la planta. En España, las zonas con focos activos son las Islas Baleares y la Comunidad Valenciana, con diferencias en cuanto a las características genéticas de los aislados bacterianos y las especies vegetales afectadas

Two Xylella fastidiosa subsp. multiplex strains isolated from almond in Spain differ in plasmid content and virulence traits

The plant pathogenic bacterium Xylella fastidiosa (Xf) is a major threat to agriculture and the environment worldwide. Recent devastating outbreaks in Europe highlight the potential of this pathogen to cause emergent diseases. Xf subsp. multiplex ESVL and IVIA5901 strains that belong to sequence type (ST) 6 were isolated from almond orchards within the outbreak area in Alicante province (Spain). Both strains share more than 99% of the chromosomal sequences), but the ESVL strain harbours two plasmids (pXF64-Hb_ESVL and pUCLA-ESVL). Here, virulence phenotypes and genome content were compared between both strains, using three strains from USA as a reference for the phenotypic analyses. Experiments in microfluidic chambers, used as simulation of xylem vessels, showed that twitching motility was absent in the IVIA5901 strain, while the ESVL strain had reduced twitching motility. Both Spanish strains had less biofilm formation, cell aggregation and lower virulence in tobacco compared with USA reference strains. Genome analysis of the two plasmids from ESVL revealed 51 unique coding sequences (CDS) that were absent in the chromosome of IVIA5901. Comparison of the chromosomes of both strains showed some unique CDS and SNPs in each strain with potential deleterious mutations. Genomic differences found in genes previously associated with adhesion and motility might explain the differences in the phenotypic traits studied. Although additional studies are necessary to infer the potential role of Xf plasmids, our results indicate that the presence of plasmids should be considered in the study of the mechanisms of pathogenicity and adaptation in Xf to new environments.Peer reviewe

Emergence of a Plant Pathogen in Europe Associated with Multiple Intercontinental Introductions

Pathogen introductions have led to numerous disease outbreaks in naive regions of the globe. The plant pathogen Xylella fastidiosa has been associated with various recent epidemics in Europe affecting agricultural crops, such as almond, grapevine, and olive, but also endemic species occurring in natural forest landscapes and ornamental plants. We compared whole-genome sequences of X. fastidiosa subspecies multiplex from America and strains associated with recent outbreaks in southern Europe to infer their likely origins and paths of introduction within and between the two continents. Phylogenetic analyses indicated multiple introductions of X. fastidiosa subspecies multiplex into Italy, Spain, and France, most of which emerged from a clade with limited genetic diversity with a likely origin in California, USA. The limited genetic diversity observed in X. fastidiosa subspecies multiplex strains originating from California is likely due to the clade itself being an introduction from X. fastidiosa subspecies multiplex populations in the southeastern United States, where this subspecies is most likely endemic. Despite the genetic diversity found in some areas in Europe, there was no clear evidence of recombination occurring among introduced X. fastidiosa strains in Europe. Sequence type taxonomy, based on multilocus sequence typing (MLST), was shown, at least in one case, to not lead to monophyletic clades of this pathogen; whole-genome sequence data were more informative in resolving the history of introductions than MLST data. Although additional data are necessary to carefully tease out the paths of these recent dispersal events, our results indicate that whole-genome sequence data should be considered when developing management strategies for X. fastidiosa outbreaks. IMPORTANCE Xylella fastidiosa is an economically important plant-pathogenic bacterium that has emerged as a pathogen of global importance associated with a devastating epidemic in olive trees in Italy associated with X. fastidiosa subspecies pauca and other outbreaks in Europe, such as X. fastidiosa subspecies fastidiosa and X. fastidiosa subspecies multiplex in Spain and X. fastidiosa subspecies multiplex in France. We present evidence of multiple introductions of X. fastidiosa subspecies multiplex, likely from the United States, into Spain, Italy, and France. These introductions illustrate the risks associated with the commercial trade of plant material at global scales and the need to develop effective policy to limit the likelihood of pathogen pollution into naive regions. Our study demonstrates the need to utilize whole-genome sequence data to study X. fastidiosa introductions at outbreak stages, since a limited number of genetic markers does not provide sufficient phylogenetic resolution to determine dispersal paths or relationships among strains that are of biological and quarantine relevance