A novel plasmid pEA68 of Erwinia amylovora and the description of a new family of plasmids.

Recent genome analysis of Erwinia amylovora, the causal agent of fire blight disease on Rosaceae, has shown that the chromosome is highly conserved among strains and that plasmids are the principal source of genomic diversity. A new circular plasmid, pEA68, was found in E. amylovora strain 692 (LMG 28361), isolated in Poland from Sorbus (mountain ash) with fire blight symptoms. Annotation of the 68,763-bp IncFIIa-type plasmid revealed that it contains 79 predicted CDS, among which two operons (tra, pil) are associated with mobility. The plasmid is maintained stably in E. amylovora and does not possess genes associated with antibiotic resistance or known virulence genes. Curing E. amylovora strain 692 of pEA68 did not influence its virulence in apple shoots nor amylovoran synthesis. Of 488 strains of E. amylovora from seventeen countries, pEA68 was only found in two additional strains from Belgium. Although the spread of pEA68 is currently limited to Europe, pEA68 comprises, together with pEA72 and pEA78 both found in North America, a new plasmid family that spans two continents.

Small subunit ribosomal DNA-based phylogenetic analysis of foliar nematodes (Aphelenchoides spp.) and their quantitative detection in complex DNA backgrounds.

Foliar nematodes, plant-parasitic representatives of the genus Aphelenchoides, constitute a minority in a group dominated by fungivorous species. Distinction between (mostly harmless) fungal feeding Aphelenchoides species and high impact plant parasites such as A. besseyi, A. fragariae, A. ritzemabosi, and A. subtenuis is severely hampered by the scarcity of informative morphological characters, some of which are only observable in specific developmental stages. Poor description of a number of non-plant-parasitic Aphelenchoides species further complicates identification. Based on (nearly) full-length small subunit ribosomal DNA (SSU rDNA) sequences (≈1,700 bp), a phylogenetic tree was generated, and the four target species appeared as distinct, well-supported groups. Notably, this genus does not constitute a monophyletic group: A. besseyi and A. ritzemabosi cluster together and they are phylogenetically isolated from A. fragariae, A. subtenuis, and most other fungivorous species. A phylum-wide SSU rDNA framework was used to identify species-specific DNA motifs. For the molecular detection of four plant-parasitic Aphelenchoides species, polymerase chain reaction primers were developed with high, identical annealing temperatures (63°C). Within the molecular framework presented here, these primers can be used for the rapid screening of plant material and soil for the presence of one or multiple foliar nematode species.

Gramicidin S derivatives containing cis- and trans-morpholine amino acids (MAAs) as turn mimetics.

The cyclic decapeptide gramicidin S (GS) was used as a model for the evaluation of four turn mimetics. For this purpose, one of the D-Phe-Pro two-residue turn motifs in the rigid cyclic beta-hairpin structure of GS was replaced with morpholine amino acids (MAA 2-5), differing in stereochemistry and length of the side-chain. The conformational properties of the thus obtained GS analogues (6-9) was assessed by using NMR spectroscopy and X-ray crystallography, and correlated with their biological properties (antimicrobial and hemolytic activity). We show that compound 8, containing the dipeptide isostere trans-MAA 4, has an apparent high structural resemblance with GS and that its antibacterial activity against a panel of Gram positive and -negative bacterial strains is better than the derivatives 6, 7 and 9.

Evaluation of a real-time PCR and a loop-mediated isothermal amplification for detection of Xanthomonas arboricola pv. pruni in plant tissue samples.

Operational capacity of real-time PCR and loop-mediated isothermal amplification (LAMP) diagnostic assays for detection of Xanthomonas arboricola pv. pruni was established in a ring-test involving four laboratories. Symptomatic and healthy almond leaf samples with two methods of sample preparation were analyzed. Kappa coefficient, sensitivity, specificity, likelihood ratios and post-test probability of detection were estimated to manage the risk associated with the use of the two methods.

The arable ecosystem as battleground for emergence of new human pathogens.

Disease incidences related to Escherichia coli and Salmonella enterica infections by consumption of (fresh) vegetables, sprouts, and occasionally fruits made clear that these pathogens are not only transmitted to humans via the "classical" routes of meat, eggs, and dairy products, but also can be transmitted to humans via plants or products derived from plants. Nowadays, it is of major concern that these human pathogens, especially the ones belonging to the taxonomical family of Enterobacteriaceae, become adapted to environmental habitats without losing their virulence to humans. Adaptation to the plant environment would lead to longer persistence in plants, increasing their chances on transmission to humans via consumption of plant-derived food. One of the mechanisms of adaptation to the plant environment in human pathogens, proposed in this paper, is horizontal transfer of genes from different microbial communities present in the arable ecosystem, like the ones originating from soil, animal digestive track systems (manure), water and plants themselves. Genes that would confer better adaptation to the phytosphere might be genes involved in plant colonization, stress resistance and nutrient acquisition and utilization. Because human pathogenic enterics often were prone to genetic exchanges via phages and conjugative plasmids, it was postulated that these genetic elements may be hold key responsible for horizontal gene transfers between human pathogens and indigenous microbes in agroproduction systems. In analogy to zoonosis, we coin the term phytonosis for a human pathogen that is transmitted via plants and not exclusively via animals.