Nicola S. Iacobellis

The structure of syringomycins A1, E and G

By a combination of 1D and 2D 1H‐ and 13C‐NMR, FAB‐MS, and chemical and enzymatic reactions carried out at the milligram level, it has been demonstrated that syringomycin E, the major phytotoxic antibiotic produced by Pseudomonas syringae pv. syringae, is a new lipodepsipeptide. Its amino acid sequence is Ser‐Ser‐Dab‐Dab‐Arg‐Phe‐Dhb‐4(Cl)Thr‐3(OH)Asp with the β‐carboxy group of the C‐terminal residue closing a macrocyclic ring on the OH group of the N‐terminal Ser, which in turn is N‐acylated by 3‐hydroxydodecanoic acid. Syringomycins A1 and G, two other metabolites of the same bacterium, differ from syringomycin E only in their fatty acid moieties corresponding, respectively, to 3‐hydroxydecanoic and 3‐hydroxytetradecanoic acid.

Phytotoxic properties of Pseudomonas syringae pv. syringae toxins

Abstract Syringomycin E, syringomycin G and syringopeptin 25A, the main components of the Pseudomonas syringae pv. syringae toxin mixture, were assayed for their phytotoxicity, determined as electrolyte leakage from carrot tissues, necrosis of tobacco leaves, and death of potato tissues, and for their antimicrobial activity on Rhodotorula pilimanae. p]In the antimicrobial assay, syringomycins were 30 times more active than syringopeptin 25A, but, in the electrolyte leakage assay, they proved to be 40 times less active than the former since a significant effect required concentrations of 16 and 0·4 μ m respectively. A statistically identical effect on electrolyte leakage was obtained with syringopeptin 25A or with an unfractionated toxin mixture equimolar for syringopeptin 25A. A similar pattern of activity was observed in the tobacco leaf and potato disc assays. After a short incubation at pH 10, syringomycins completely lost their antimicrobial and phytotoxic activities, while syringopeptin 25A retained all its antimicrobial activity and most of its phytotoxicity. These findings indicate that syringopeptin 25A and syringomycins are mainly responsible for, respectively, the phytotoxic activity and the antimicrobial activity on R. pilimanae, characteristic of the unfractionated toxin mixture of P. s. pv. syringae. The high phytotoxicity of syringopeptin 25A is a new finding which prompts a careful examination of the role played by the individual metabolites in the disease caused by P. s. pv. syringae ecotypes.

Structure of syringotoxin, a bioactive metabolite of Pseudomonas syringae pv. syringae

The covalent structure of syringotoxin, a bioactive metabolite of Pseudomonas syringae pv. syringae isolates, pathogenic on various species of citrus trees, has been deduced from ID and 2D 1H‐ and 13C‐NMR spectra combined with extensive FAB‐MS data and results of some chemical reactions. Similarly to syringomicins and syringostatins, produced by other plant pathogenic strains of P. syringae pv. syringae, syringotoxin is a lipodep‐sinonapeptide. Its peptide moiety corresponds to Ser‐Dab‐Gly‐Hse‐Om‐aThr‐Dhb‐(3‐OH)Asp‐(4‐Cl)Thr with the terminal carboxy group closing a macrocyclic ring on the OH group of the N‐terminal Ser, which in turn is N‐acetylated by 3‐hydroxytetradecanoic acid.

Antibacterial Activity of Essential Oil Components and Their Potential Use in Seed Disinfection

Among the main (> or = 0.7%) components of some essential oils, considerable antibacterial activity was shown by terpenoid and phenylpropanoid derivatives containing phenol and alcohol functionalities. A reduced or no activity was shown by those derivatives containing ketones, aldehydes, ethers, and ester functionalities as well as the remaining terpenoids. Eugenol emulsion treatments (1-8 mg/mL) of bean seeds bearing about 2.6 x 10(6) cfu/seed of strain ICMP239 of Xanthomonas campestris pv. phaseoli var. fuscans determined a highly significant reduction of the bacteria on seeds. In particular, eugenol at 4 mg/mL disinfect seeds bearing about 7.0 x 10(2) cfu/seed and lower densities. However, after 72 h, incubation treatments with 2, 4, and 8 mg/mL of eugenol caused germination reduction of 3%, 7%, and 16%, respectively, which was significantly different from the controls. No effect on germination was observed with 1 mg/mL eugenol emulsion treatment. These data indicate eugenol as potentially useful for bean seed disinfection from X. campestris pv. phaseoli var. fuscans. Further studies on the effects on seed vitality and on formulation of essential oils are needed.

Multiple forms of syringomycin

Abstract Preparations of syringomycin purified from three isolates of Pseudomonas syringae pv. syringae according to published procedures have been shown to contain a group of structurally related peptides which can be resolved by HPLC on a reverse phase column. In the acid hydrolysate of all components serine, phenylalanine, 2,4-diaminobutyric acid and arginine in the ratio 2:1:2:1 have been found. These products account for nearly 50% of the molecular weights determined by FAB mass spectrometry. Most of the antibiotic activity of the unfractionated preparations is recovered in a limited number of peaks.

A cytokinin from the culture filtrate of Pseudomonas syringae pv. savastanoi

Abstract The structure of a new cytokinin, isolated from the culture filtrate of Pseudomonas syringae pv. savastanoi, is assigned on the basis of spectroscopic data including its tetracetyl derivative and comparison with related adenine derivatives. It was identified as 6-(4-hydroxy-1,3-dimethylbut-trans-2-enylamino-9-β- D -ribofuranosyl)purine.

In Vitro Antifungal Activity of Burkholderia gladioli pv. agaricicola against Some Phytopathogenic Fungi

The trend to search novel microbial natural biocides has recently been increasing in order to avoid the environmental pollution from use of synthetic pesticides. Among these novel natural biocides are the bioactive secondary metabolites of Burkholderia gladioli pv. agaricicola (Bga). The aim of this study is to determine antifungal activity of Bga strains against some phytopathogenic fungi. The fungicidal tests were carried out using cultures and cell-free culture filtrates against Botrytis cinerea, Aspergillus flavus, Aspergillus niger, Penicillium digitatum, Penicillium expansum, Sclerotinia sclerotiorum and Phytophthora cactorum. Results demonstrated that all tested strains exert antifungal activity against all studied fungi by producing diffusible metabolites which are correlated with their ability to produce extracellular hydrolytic enzymes. All strains significantly reduced the growth of studied fungi and the bacterial cells were more bioactive than bacterial filtrates. All tested Bulkholderia strains produced volatile organic compounds (VOCs), which inhibited the fungal growth and reduced the growth rate of Fusarium oxysporum and Rhizoctonia solani. GC/MS analysis of VOCs emitted by strain Bga 11096 indicated the presence of a compound that was identified as 1-methyl-4-(1-methylethenyl)-cyclohexene, a liquid hydrocarbon classified as cyclic terpene. This compound could be responsible for the antifungal activity, which is also in agreement with the work of other authors.

Pseudomonas syringae and related pathogens

Since the early 1990s, bacterial blight has emerged as an important disease of cantaloupe in France, particularly in the south-west but has caused epidemics in all the production regions of this country. The pathogen is a complex composed of strains identified as Pseudomonas syringae pv. aptata (70% of the strains) and the remaining resembling P. viridijlava (2%), P. s. pv. lachrymans (1%) or P. syringae in general but with no correspondence to a known pathovar. To investigate the epidemiology of this disease and to develop disease control strategies, we have attempted to identify sources of inoculum in the field, factors contributing to the explosive development of the disease, resistance of the bacterium to copper pesticides, and sources of disease resistance in Cucumis melo. Based on our observations and on the description of possible outbreaks of this disease elsewhere in the world, we report here a hypothetical scenario of the critical factors triggering disease development and of the potential efficiency of different control strategies.

A new syringopeptin produced by bean strains of Pseudomonas syringae pv. syringae.

Two strains (B728a and Y37) of the phytopathogenic bacterium Pseudomonas syringae pv. syringae isolated from bean (Phaseolus vulgaris) plants were shown to produce in culture both syringomycin, a lipodepsinonapeptide secreted by the majority of the strains of the bacterium, and a new form of syringopeptin, SP(22)Phv. The structure of the latter metabolite was elucidated by the combined use of mass spectrometry (MS), nuclear magnetic resonance (NMR) spectroscopy and chemical procedures. Comparative phytotoxic and antimicrobial assays showed that SP(22)Phv did not differ substantially from the previously characterized syringopeptin 22 (SP(22)) as far as toxicity to plants was concerned, but was less active in inhibiting the growth of the test fungi Rhodotorula pilimanae and Geotrichum candidum and of the Gram-positive bacterium Bacillus megaterium.

Pseudomonas syringae Pathovars and Related Pathogens – Identification, Epidemiology and Genomics

Preface. Sponsors and Donors. Section 1. Identification and Detection. 1. Current technologies for Pseudomonas spp. and Ralstonia solanacearum detection and molecular typing: M.M. Lopez et al. 2. Siderophore uses in Pseudomonas syringae identification: A. Bultreys, I. Gheysen. 3. Chlorophyll fluorescene imaging for detection of Bean response to Pseudomonas syringae in asymptomatic leaf areas: L. Rodrigues-Moreno et al. 4. Sensitive detection of Ralstonia solanacearum (race 3) using serological methods and Biolog automated system: A.E. Tawfik et al. Section 2. Epidemiology and Disease Management. 5. Epidemiological basis for an efficient control of Pseudomonas savastanoi pv. savastanoi on olive trees: J.M. Quesada et al. 6. Pseudomonas syringae pv. syringae on kiwifruit plants: its role and its control: A. Rossetti and G.M. Balestra. 7. Head rot of cauliflower caused by Pseudomonas fluerescens in southern Italy: P. Lo Cantore and N.S. Iacobellis. 8. Internalization and survival of Pseudomonas corrugata from flowers to fruits and seeds of tomato plants: G. Cirvilleri et al. 9. Copper and streptomycin resistance in pseudomonas strains isolated from pipfruit and stone fruit orchards in New Zealand: J.L. Vanneste et al. 10. Basal defence in Arabidopsis agains Pseudomonas syringae pv. phaseolicola: Beyond FLS2?: A. Forsyth et al. 11. Agrobacterium suppresses P. syringae-elicited salicylate production in Nicotiana tabacum leaves: A. Rico and G.M. Preston. 12. Characterization of an inhibitory strain of Pseudomonas syringae pv. syringae withpotential as a biocontrol agent for bacterial blight on soybean: S.D. Braun and B. Volksch. 13. Characterization of the inhibitory strain Pantoea sp. 48b/90 with potential as a biocontrol agent for bacterial plant pathogens: B. Volksch and U. Sammer. 14. Pseudomonas syringae: Prospects for its use as a weed biocontrol agent: B.M. Thompson et al. 15. Analysis of Pseudomonas syringae populations and identification of strains as potential biocontrol agents against postharvest rot of different fruits: G. Cirvilleri et al. Section 3. Pathogenesis and Determinants of Pathogenicity. 16. The distribution of multiple exopolysaccharides in Pseudomonas syringae biofilms: H. Laue et al. 17. Impact of temperature on the regulation of coronatine biosyntesis in Pseudomonas syringae: Y. Braun et al. 18. Role of flagelling glycosylation in bacterial virulence: Y. Ichinose et al. 19. Genetic relatedness among the different genetic lineages of Pseudomonas syringae pv. phaseolicola: M.E. Fuhrer et al. 20. WLIP and Analogues of Tolaasin I, Lipodepsipeptides from Pseudomonas reactans and Pseudomonas tolaasii: A Comparison of their Activity on Natural and Model Membranes: R. Paletti et al. 21. Competitive index in mixed infection: a sensitive and accurate method to quantify growth of pseudomonas syringae in different plants: A.P. Macho et al. Section 4. Genomics and Molecular Characterization. 22. Genomic analysis of Pseudomonas syringae pathovars: Identification of virulence genes and associated regulatory elements using pattern-based searches and genome comparison: W. Lindeberg et al. 23. Gene ontology (GO) for microbe-host interactions and its