Volcanic impacts on peatland microbial communities: A tephropalaeoecological hypothesis-test

Volcanic eruptions affect peatlands around the world, depositing volcanic ash (tephra) and a variety of chemicals including compounds of sulphur. These volcanic impacts may be important for many reasons, in particular sulphur deposition has been shown to suppress peatland methane flux, potentially reinforcing climatic cooling. Experiments have shown that sulphur deposition also forces changes in testate amoeba communities, potentially relating to the reduced methane flux. Large volcanic eruptions in regions with extensive peatlands are relatively rare so it is difficult to assess the extent to which volcanic eruptions affect peatland microbial communities; palaeoecological analyses across tephra layers provide a means to resolve this uncertainty. In this study, testate amoebae were analysed across multiple monoliths from a peatland in southern Alaska containing two tephras, probably representing the 1883 eruption of Augustine Volcano and a 20th Century eruption of Redoubt Volcano. Results showed relatively distinct and often statistically significant changes in testate amoeba community coincident with tephra layers which largely matched the response found in experimental studies of sulphur deposition. The results suggest volcanic impacts on peatland microbial communities which might relate to changes in methane flux

Erwinia amylovora Novel Plasmid pEI70: Complete Sequence, Biogeography, and Role in Aggressiveness in the Fire Blight Phytopathogen

Comparative genomics of several strains of Erwinia amylovora, a plant pathogenic bacterium causal agent of fire blight disease, revealed that its diversity is primarily attributable to the flexible genome comprised of plasmids. We recently identified and sequenced in full a novel 65.8 kb plasmid, called pEI70. Annotation revealed a lack of known virulence-related genes, but found evidence for a unique integrative conjugative element related to that of other plant and human pathogens. Comparative analyses using BLASTN showed that pEI70 is almost entirely included in plasmid pEB102 from E. billingiae, an epiphytic Erwinia of pome fruits, with sequence identities superior to 98%. A duplex PCR assay was developed to survey the prevalence of plasmid pEI70 and also that of pEA29, which had previously been described in several E. amylovora strains. Plasmid pEI70 was found widely dispersed across Europe with frequencies of 5–92%, but it was absent in E. amylovora analyzed populations from outside of Europe. Restriction analysis and hybridization demonstrated that this plasmid was identical in at least 13 strains. Curing E. amylovora strains of pEI70 reduced their aggressiveness on pear, and introducing pEI70 into low-aggressiveness strains lacking this plasmid increased symptoms development in this host. Discovery of this novel plasmid offers new insights into the biogeography, evolution and virulence determinants in E. amylovora

Utilisation de la production de métabolites secondaires de types phytoxine et sidérophore en vue de la caractérisation et de l'identification de Pseudomonas syringae

L'étude de la production de phytotoxines et de sidérophores de type pyoverdine par des souches de Pseudomonassyringae pv. syringae et de P. syringae pv. morsprunorum a été réalisée en vue de caractériser les souches concernant la capacité de production de ces types de métabolites secondaires et en vue de déterminer dans quelle mesure ces métabolites permettent de différencier les pathovars, de les classifier, voire de les identifier.Les conditions favorisant la production de lipodepsipeptides toxiques et de pyoverdines ont été étudiées. Des milieux de culture et des techniques de production ont été définis en culture solide et en culture liquide. Les résultats de ces travaux permettent de penser que les conditions nécessaires à la production de ces métabolites par P. syringae sont probablement régulièrement rencontrées sur la plante.Un test biologique détectant la capacité de production de lipodepsipeptides toxiques et un test PCR détectant le gène syrDimpliqué dans leur production ont été développés pour détecter les souches de P. syringae produisant ces phytotoxines. La capacité de souches de P. syringae pv. morsprunorum à produire de la coronatine a par ailleurs été déterminée par l'utilisation d'un test biologique et d'un test PCR détectant le gène cfl.La diversité des pyoverdines produites dans les espèces P. syringae et Pseudomonas viridiflava a été déterminée par purification chimique et caractérisation des molécules, ce qui a permis de constater que ces espèces produisent une même pyoverdine atypique ayant des caractéristiques différentes de celles des pyoverdines habituelles. Les souches non fluorescentes de P. syringaepv. morsprunorum sont par ailleurs capables d'utiliser les pyoverdines produites par les souches fluorescentes de l'espèce, ainsi que les dihydropyoverdines produites par certaines souches non fluorescentes, malgré qu'elles ne produisent apparemment pas ces molécules. La mise en évidence des caractéristiques inhabituelles des pyoverdines et dihydropyoverdines de P. syringae a permis la proposition de tests de caractérisation et d'identification basés sur ces sidérophores. Les pouvoirs discriminatoires des différents tests proposés ont été déterminés par l'étude de pathovars distants de P. syringae et par l'étude d'espèces proches et plus éloignées. Les résultats des comparaisons des espèces ont été confirmés par la caractérisation des pyoverdines produites par les espèces Pseudomonas ficuserectae, Pseudomonas cichorii, Pseudomonas asplenii et Pseudomonas fuscovaginae qui produisent également des pyoverdines atypiques. La détection des sidérophores par HPLC est la technique la plus performante pour différencier les différentes molécules et elle permet l'identification directe des souches dans plusieurs cas. Les tests sur les sidérophores permettent la différentiation rapide et aisée des souches des espèces du groupe taxonomique des Pseudomonas fluorescents phytopathogènes, producteurs de pyoverdines atypiques, des souches des espèces du groupe taxonomique des Pseudomonas fluorescents saprophytes qui produisent des pyoverdines typiques, ce qui confère à ces tests un intérêt indéniable dans la pratique.Les tests portant sur la production de phytotoxines et de sidérophores ont été utilisés dans la pratique pour caractériser et pour identifier des souches isolées de vergers belges. Ils ont mis en évidence des différences entre des isolats issus de différentes cultures et de différents organes et ils ont permis de grandement accélérer la procédure d'identification des souches de P. syringae. Les tests PCR ont par ailleurs montré leur grand potentiel pour détecter les pathogènes directement dans les tissus malades.Doctorat en sciences agronomiques et ingénierie biologique (AGRO 3)--UCL, 200

Yersiniabactin Production by Pseudomonas syringae and Escherichia coli, and Description of a Second Yersiniabactin Locus Evolutionary Group

The siderophore and virulence factor yersiniabactin is produced by Pseudomonas syringae. Yersiniabactin was originally detected by high-pressure liquid chromatography (HPLC); commonly used PCR tests proved ineffective. Yersiniabactin production in P. syringae correlated with the possession of irp1 located in a predicted yersiniabactin locus. Three similarly divergent yersiniabactin locus groups were determined: the Yersinia pestis group, the P. syringae group, and the Photorhabdus luminescens group; yersiniabactin locus organization is similar in P. syringae and P. luminescens. In P. syringae pv. tomato DC3000, the locus has a high GC content (63.4% compared with 58.4% for the chromosome and 60.1% and 60.7% for adjacent regions) but it lacks high-pathogenicity-island features, such as the insertion in a tRNA locus, the integrase, and insertion sequence elements. In P. syringae pv. tomato DC3000 and pv. phaseolicola 1448A, the locus lies between homologues of Psyr_2284 and Psyr_2285 of P. syringae pv. syringae B728a, which lacks the locus. Among tested pseudomonads, a PCR test specific to two yersiniabactin locus groups detected a locus in genospecies 3, 7, and 8 of P. syringae, and DNA hybridization within P. syringae also detected a locus in the pathovars phaseolicola and glycinea. The PCR and HPLC methods enabled analysis of nonpathogenic Escherichia coli. HPLC-proven yersiniabactin-producing E. coli lacked modifications found in irp1 and irp2 in the human pathogen CFT073, and it is not clear whether CFT073 produces yersiniabactin. The study provides clues about the evolution and dispersion of yersiniabactin genes. It describes methods to detect and study yersiniabactin producers, even where genes have evolved

Genetic analyses od Pseudomonas syringae isolates from Belgian fruit orchards reveal genetic variability and isolate-host relationship within the pathovar syringae and help identify both races of the pathovar morsprunorum

A collection of Pseudomonas syringae and viridiflava isolates was established between 1993 and 2002 from diseased organs sampled from 36 pear, plum and cherry orchards in Belgium . Among the 356 isolates investigated in this study, phytotoxin, siderophore and classical microbiology tests, as well as the genetical methods REP-, ERIC- and BOX-(collectively, rep-) and IS50-PCR, enabled identification to be made of 280 isolates as P. syringae pv. syringae (Pss), 41 isolates as P.syringae pv. morsprunorum (Psm) race 1, 12 isolates as Psm race 2, three isolates as P. viridiflava and 20 isolates as unclassified P. syringae. The rep-PCR methods, particularly BOX-PCR proved to be useful for identifying the Psm race 1 and Ps race 2 isolates. The latter race was frequent on sour cherry in Belgium . Combined genetic results confirmed homogeneities in the pvs avii, and morsprunorum race 1 and race 2 and high diversity in the pv. syringae. In the pv. syringae, homogeneous genetic groups consistently found on the same hosts (pear, cherry or plum) were observed. Pathogenicity on lilac was sometimes variable among Pss isolates from the same genetic group; also,some Psm race 2 and unclassified P. syringae isolates were pathogenic to lilac. In the BOX analyses four patterns included 100% of the toxic lipodepsipeptide(TLP)-producing Pss isolates pathogenic to lilac. Many TLP-producing Pss isolates non-pathogenic to lilac and the TLP-non-producing Pss isolates were classified differently. Pseudomonas syringae isolates that differed from known fruit pathogens were observed in pear, sour cherry and plum orchards in Belgium

Nicotiana plumbaginifolia plants silenced for the ATP-binding cassette transporter gene NpPDR1 show increased susceptibility to a group of fungal and oomycete pathogens

P>The behaviour of Nicotiana plumbaginifolia plants silenced for the ATP-binding cassette transporter gene NpPDR1 was investigated in response to fungal and oomycete infections. The importance of NpPDR1 in plant defence was demonstrated for two organs in which NpPDR1 is constitutively expressed: the roots and the petal epidermis. The roots of the plantlets of two lines silenced for NpPDR1 expression were clearly more sensitive than those of controls to the fungal pathogens Botrytis cinerea, Fusarium oxysporum sp., F. oxysporum f. sp. nicotianae, F. oxysporum f. sp. melonis and Rhizoctonia solani, as well as to the oomycete pathogen Phytophthora nicotianae race 0. The Ph gene-linked resistance of N. plumbaginifolia to P. nicotianae race 0 was totally ineffective in NpPDR1-silenced lines. In addition, the petals of the NpPDR1-silenced lines were spotted 15%-20% more rapidly by B. cinerea than were the controls. The rapid induction (after 2-4 days) of NpPDR1 expression in N. plumbaginifolia and N. tabacum mature leaves in response to pathogen presence was demonstrated for the first time with fungi and one oomycete: R. solani, F. oxysporum and P. nicotianae. With B. cinerea, such rapid expression was not observed in healthy mature leaves. NpPDR1 expression was not observed during latent infections of B. cinerea in N. plumbaginifolia and N. tabacum, but was induced when conditions facilitated B. cinerea development in leaves, such as leaf ageing or an initial root infection. This work demonstrates the increased sensitivity of NpPDR1-silenced N. plumbaginifolia plants to all of the fungal and oomycete pathogens investigated