Publications

4475

‘ Candidatus Liberibacter asiaticus’ ( CL as) is associated with the most destructive disease of citrus, huanglongbing ( HLB ). The most widely used methods for detection of CL as are PCR ‐based and require purification of DNA from plant samples. Elution of DNA from tissue prints made on nitrocellulose membranes followed by qPCR ( TPE ‐ qPCR ) was compared to DNA extraction of plant tissue followed by PCR (X‐ PCR ) by testing the same tissue samples. The former estimated a higher CL as population in tissue prints than the latter ( t ‐test; P  =   0.009). All extracts prepared for TPE ‐ qPCR throughout the experiment were also tested by conventional PCR and 80.8% were identified as positive. A similar set of stem and petiole tissue samples was tested by TPE ‐ qPCR and immunoassay. Although the detection rate by TPE ‐ qPCR was higher than by immunoassay, about 6% of tissue prints were positive by immunoassay but not by TPE ‐ qPCR . Thus, a higher detection rate would be achieved by combining TPE ‐ qPCR with immunoassay. Significant differences were observed in the performance of nitrocellulose membranes from different manufacturers in these assays. Immunotissue prints showed that the spatial distribution pattern of CL as infection varied widely from one sample to another, but the patterns were highly correlated among serial sections from the same sample, suggesting that CL as preferentially colonizes adjacent phloem cells in a vertical rather than horizontal direction.

Abstract‘Candidatus Liberibacter solanacearum’ (Lso) has emerged as a serious threat on solanaceous and apiaceous crops worldwide. Five Lso haplotypes (LsoA, LsoB, LsoC, LsoD and LsoE) have been identified so far. To decipher genetic relationships between Lso strains, a MLSA study of seven housekeeping genes (acnA, atpD, ftsZ, glnA, glyA, gnd and groEL) was performed on a representative bacterial collection of 49 Lso strains. In all, 5415 bp spanning the seven loci were obtained from each of the 49 strains of our bacterial collection. Analysis of sequence data was consistent with a clonal population structure with no evidence of recombination. Phylogenies reconstructed from individual genes, and with concatenated data, were globally congruent with each other. In addition to the five highly supported and distinct genetic clusters, which correspond to the five established haplotypes, our phylogenetic data revealed the presence of a sixth haplotype, designated ‘LsoG’. This new haplotype is currently represented by two strains from France which had distinct sequences in four out of the seven tested housekeeping genes. Altogether, the data presented here provide new information regarding the genetic structure of Lso and the evolutionary history of the haplotypes defined within this bacterial species.

Here, we report the draft genome sequence of a phytoplasma discovered in grapevine. The genome size is 600,116 nucleotides (nt), with 597 predicted open reading frames.

Abstract Large reservoirs of natural gas in the oceanic subsurface sustain complex communities of anaerobic microbes, including archaeal lineages with potential to mediate oxidation of hydrocarbons such as methane and butane. Here we describe a previously unknown archaeal phylum, Helarchaeota, belonging to the Asgard superphylum and with the potential for hydrocarbon oxidation. We reconstruct Helarchaeota genomes from metagenomic data derived from hydrothermal deep-sea sediments in the hydrocarbon-rich Guaymas Basin. The genomes encode methyl-CoM reductase-like enzymes that are similar to those found in butane-oxidizing archaea, as well as several enzymes potentially involved in alkyl-CoA oxidation and the Wood-Ljungdahl pathway. We suggest that members of the Helarchaeota have the potential to activate and subsequently anaerobically oxidize hydrothermally generated short-chain hydrocarbons.

Coconut is an important crop for both industry and small stakeholders in many intertropical countries. Phytoplasma-associated lethal yellowing-like diseases have become one of the major pests that limit coconut cultivation as they have emerged in different parts of the world. We developed a multilocus sequence typing scheme (MLST) for tracking epidemics of “ Ca . Phytoplasma palmicola,” which is responsible for coconut lethal yellowing disease (CLYD) on the African continent. MLST analysis applied to diseased coconut samples collected in western and eastern African countries also showed the existence of three distinct populations of “ Ca . Phytoplasma palmicola” with low intrapopulation diversity. The reasons for the observed strong geographic patterns remain to be established but could result from the lethality of CLYD and the dominance of short-distance insect-mediated transmission.

El Huanglongbing representa un gran reto para su control, por lo que se requiere de alternativas efectivas a la aplicación de insecticidas al insecto vector. La inducción de resistencia sistémica es una alternativa para disminuir el progreso de la enfermedad en árboles infectados. El objetivo de este trabajo fue evaluar el efecto de inductores de resistencia sistémica sobre la concentración de <em>?Candidatus</em> Liberibacter asiaticus? (CLas) en árboles de limón mexicano (Lm) en condiciones de invernadero. Los inductores de resistencia utilizados fueron ácido salicílico (T1), <em>Azospirillum brasilense</em> Cd (T2) y quitosano (T3), aplicados cada 20 días durante ocho meses. La cuantificación de CLas fue mediante qPCR. La concentración de CLas se determinó a los 1, 2, 5 y 8 meses pos-tratamiento. A los 8 meses pos-tratamiento, T1 y T3 no presentaron diferencias postratamiento en la reducción postratamiento de la concentración de CLas con respecto al control sin inductor (T4) (6.5×103 células bacterianas/100 ng de ADN), mientras que T2 disminuyó casi tres veces la concentración de CLas con respecto al control. La inoculación directa al suelo de <em>A. brasilense</em> Cd mostró un efecto significativo en la reducción de la concentración de CLas en los árboles de Lm en condiciones de invernadero.

Unplanned oil spills during offshore production are a serious problem for the industry and the marine environment. Here, we present the genome sequence analysis of three novel hydrocarbon-degrading bacteria, namely, “ Candidatus Colwellia aromaticivorans” sp.

AbstractCandidatusLiberibacter solanacearum (CLso) is an economically important plant-pathogen of tomato (Solanum lycopersicum) crops in the United States, Mexico, Central America, and New Zealand. Currently, there are no reports of resistance toCLsoin tomato cultivars. Identification and development ofCLso-resistant cultivars may offer the most efficient way to manage this tomato disease. Resistance of 46 tomato landraces collected in different regions of Mexico, representing a wide range of genetic variability from this country was evaluated. Two assays were done in consecutively years to assess the resistance toCLsounder greenhouse conditions. Plants from both tests were inoculated withCLsothrough 20Bactericera cockerelliinsects per plant. In the first trial, landraces FC22 and FC44 showed a significantly higher proportion of resistant plants, less symptoms severity, and longer incubation time, followed by landraces FC40 and FC33 compared with the rest of the 42 landraces and 2 susceptible cultivars 60 days post inoculation (dpi). In the second assay, only landraces FC22 and FC44 had again significantly higher proportion of resistant plants, less symptoms severity, relative lowerCLsotiters, and longer incubation time in comparison with landraces FC40 and FC33 and the two susceptible cultivars 60 dpi, corroborating their resistance toCLso. Presence ofCLsoDNA in all resistant plants from both assays discards scape plants and indicates that the methodology used was adequate to discriminate between resistant and susceptible plants. These results confirm that landraces FC22 and FC44 are promising resistant sources for the development ofCLso-resistant cultivars of tomato.Author summaryThe bacterium “CandidatusLiberibacter solanacearum” (CLso) is an important plant-pathogen of tomato crops in the United States, Mexico, Central America, and New Zealand. Tomato growers are lacking of cultivars with resistance to this pathogen and the development of resistant cultivars of this crop would make a sustainable business for these growers and healthy tomato consumption for humans. Tomato landraces from countries that are center of domestication of cultivated crops like Mexico, are potentially sources of resistance to plant-pathogens. Therefore, two tests were done looking for resistance sources to this pathogen and we found two tomato landraces (FC22 and FC44) showing high level of resistance toCLsobecause they had significantly higher resistant plants, less symptoms severity, lowerCLsoDNA concentration, and delay of the first symptoms in the inoculated plants in comparison with the two commercial cultivars and 44 tomato landraces collected from Mexico 60 days post infection. These landraces are promising resistant sources for the development ofCLso-resistant cultivars of tomato.