Publications

3534

In this paper, a comprehensive overview of the ‘Candidatus Liberibacter solanacearum’ presence in Europe was provided. The analyzed findings revealed that, since the first appearance of this pathogen in Finland and Spain in 2008, it has spread to 13 new European countries. Therefore, ‘Ca. L. solanacearum’ has spread very quickly across the European continent, as evident from the emergence of new host plants within the Apiaceae, Urticaceae, and Polygonaceae families, as well as new haplotypes of this pathogen. Thus far, 5 of the 15 ‘Ca. L. solanacearum’ haplotypes determined across the globe have been confirmed in Europe (haplotypes C, D, E, U, and H). Fully competent ‘Ca. L. solanacearum’ vectors include Bactericera cockerelli, Trioza apicalis, and B. trigonica; however, only T. apicalis and B. trigonica are presently established in Europe and are very important for plants from the Apiaceae family in particular. Moreover, psyllid species such as B. tremblayi, T. urticae, and T. anthrisci have also been confirmed positive for ‘Ca. L. solanacearum’. Constant monitoring of its spread in the field (in both symptomatic and asymptomatic plants), use of sensitive molecular diagnostic techniques, and application of timely management strategies are, therefore, of utmost importance for the control of this destructive pathogen.

In São Paulo State, Brazil, ‘Candidatus Liberibacter americanus’ and ‘Candidatus Liberibacter asiaticus’ are associated with huanglongbing (HLB). Affected municipalities occur mainly in the central and southern regions, where the annual number of hours above 30°C is two to five times lower than that in the extreme northern and western regions. The influence of temperature on sweet orange trees infected with ‘Ca. L. asiaticus’ or ‘Ca. L. americanus’ was studied in temperature-controlled growth chambers. Symptom progression on new shoots of naturally infected and experimentally graft-inoculated symptomatic sweet orange trees was assessed. Mottled leaves developed on all infected trees at 22 to 24°C, but not on any ‘Ca. L. americanus’–infected trees at 27 to 32°C. Quantitative, real time-PCR was used to determine the liberibacter titers in the trees. After 90 days, ‘Ca. L. asiaticus’–infected trees had high titers at 32 and 35°C, but not at 38°C, while ‘Ca. L. americanus’–infected trees had high titers at 24°C, but at 32°C the titers were very low or the liberibacters could not be detected. Thus, the multiplication of ‘Ca. L. asiaticus’ is not yet affected at 35°C, while a temperature of 32°C is detrimental to ‘Ca. L. americanus’. Thus, ‘Ca. L. americanus’ is less heat tolerant than ‘Ca. L. asiaticus’. The uneven distribution of these two liberibacters in São Paulo State might be in relation with these results.

AbstractThe subsurface biosphere is largely unexplored and contains a broad diversity of uncultured microbes1. Despite being one of the few prokaryotic lineages that is cosmopolitan in both the terrestrial and marine subsurface2–4, the physiological and ecological roles of SAGMEG (South-African Gold Mine Miscellaneous Euryarchaeal Group) Archaea are unknown. Here, we report the metabolic capabilities of this enigmatic group as inferred from genomic reconstructions. Four high-quality (63–90% complete) genomes were obtained from White Oak River estuary and Yellowstone National Park hot spring sediment metagenomes. Phylogenomic analyses place SAGMEG Archaea as a deeply rooting sister clade of the Thermococci, leading us to propose the name Hadesarchaea for this new Archaeal class. With an estimated genome size of around 1.5 Mbp, the genomes of Hadesarchaea are distinctly streamlined, yet metabolically versatile. They share several physiological mechanisms with strict anaerobic Euryarchaeota. Several metabolic characteristics make them successful in the subsurface, including genes involved in CO and H2 oxidation (or H2 production), with potential coupling to nitrite reduction to ammonia (DNRA). This first glimpse into the metabolic capabilities of these cosmopolitan Archaea suggests they are mediating key geochemical processes and are specialized for survival in the subsurface biosphere.

<p>Las bacterias causantes del huanglongbing (HLB), <em>Canditatus</em> Liberibacter spp., son bacterias obligadas al floema de los cítricos y a diferentes sistemas del insecto vector,<em> Diaphorina citri</em>, por lo tanto, el enfoque genómico ha sido útil para estudiar sus mecanismos de patogenicidad. Dicho enfoque ha permitido identificar una copia homóloga del gen codificante de la enzima ATP/ADP translocasa, la cual tiene la capacidad de importar ATP y nucleótidos desde el hospedante, causando un parasitismo de energía considerable. Esta enzima se ha relacionado con la actividad endoparasítica de patógenos animales y humanos más que con fitopatógenos. El presente trabajo analizó la relación evolutiva entre la secuencia de aminoácidos de la ATP/ADP translocasa entre diferentes especies de <em>Ca</em>. Liberibacter y grupos como <em>Ricketssia</em> sp. y <em>Chlamydia</em> sp. Análisis filogenéticos muestran que la variación en la secuencia del gen codificante de la enzima está delimitada en clados correspondientes a las especies de <em>Ca</em>. Liberibacter, sugiriendo que la variación en la enzima responde a un proceso coevolutivo con los hospederos. Asimismo, la filogenia muestra que el ancestro común más cercano a <em>Ca</em>. Liberibacter podría ser un endosimbionte no patogénico del género <em>Ca</em>. Midichloria. Análisis de conservación de la secuencia de aminoácidos muestran que existen varias posiciones en la secuencia que podrían estar relacionadas con la variación específica de esta enzima dentro de <em>Ca</em>. Liberibacter. Este trabajo presenta la hipótesis de que el origen evolutivo de la capacidad de parasitismo energético del género <em>Ca</em>. Liberibacter, causantes del HLB, es un endosimbionte no patogénico.</p>