RESUMEN
AIMS: Broad-spectrum antibiotics produced by symbiotic bacteria [entomopathogenic bacterium (EPB)] of entomopathogenic nematodes keep monoxenic conditions in insect cadavers in soil. This study evaluated antibiotics produced by EPB for their potential to control plant pathogenic bacteria and oomycetes. METHODS AND RESULTS: Entomopathogenic bacterium produce antibiotics effective against the fire blight bacterium Erwinia amylovora, including streptomycin resistant strains, and were as effective in phytotron experiments as kasugamycin or streptomycin. Xenorhabdus budapestensis and X. szentirmaii antibiotics inhibited colony formation and mycelial growth of Phytophthora nicotianae. From X. budapestensis, an arginine-rich fraction (bicornutin) was adsorbed by Amberlite((R)) XAD 1180, and eluted with methanol : 1 n HCI (99 : 1). Bicornutin inactivated zoospores, and inhibited germination and colony formation of cystospores at <<25 ppm. An UV-active molecule (bicornutin-A, MW = 826), separated by HPLC and thin-layer chromatography, was identified as a novel hexa-peptide : RLRRRX. CONCLUSIONS: Xenorhabdus budapestensis produces metabolites with strong antibacterial and cytotoxic activity. Individual compounds can be isolated, identified and patented, but their full antimicrobial potential may be multiplied by synergic interactions. SIGNIFICANCE AND IMPACT OF THE STUDY: Active compounds of two new Xenorhabdus species might control plant diseases caused by pathogens of great importance to agriculture such as Erw. amylovora and P. nicotianae.
Asunto(s)
Antibacterianos/farmacología , Erwinia amylovora/efectos de los fármacos , Malus/microbiología , Photorhabdus/metabolismo , Phytophthora/efectos de los fármacos , Xenorhabdus/metabolismo , Antibacterianos/aislamiento & purificación , Erwinia amylovora/crecimiento & desarrollo , Pruebas de Sensibilidad Microbiana , Phytophthora/crecimiento & desarrollo , Hojas de la Planta/microbiologíaRESUMEN
AIMS: The role of antibiotics produced by bacterial symbionts of entomopathogenic nematodes is to suppress growth of microbes in the soil environment. These antibiotics are active against Gram-positive and Gram-negative bacteria, and were tested against mastitis isolates from dairy cows. METHODS AND RESULTS: Two bioassays were adapted for Xenorhabdus antibiotics; an overlay method on agar plates, and serially diluted, cell-free, Xenorhabdus cultures. The antimicrobial activities of the liquid cultures of 13 strains from five Xenorhabdus species were further evaluated. Antimicrobial activities of the type strains of X. nematophila, X. budapestensis and X. szentirmaii were tested on mastitis isolates of Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae with both bioassays. A previously reported antibiotic from X. nematophila, nematophin, was synthesized in three steps from tryptamine and 4-methyl-2-oxovaleric acid sodium salt. CONCLUSIONS: The antibiotics of all three Xenorhabdus strains were powerful in either bioassay, but the sensitivity of the isolates differed from each other. While Kl. pneumoniae was the least susceptible, Staph. aureus had the highest sensitivity to each Xenorhabdus strain. Xenorhabdus szentirmaii and X. budapestensis were more potent antibiotic producers than X. nematophila, and raceme nematophin was ineffective against all mastitis isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: These results indicate that Xenorhabdus antibiotics are effective against mastitis isolates and should be further evaluated for their potential in mastitis control or prevention.
Asunto(s)
Antibacterianos/biosíntesis , Mastitis Bovina/tratamiento farmacológico , Microbiología del Suelo , Xenorhabdus/metabolismo , Animales , Antibacterianos/farmacología , Antibacterianos/uso terapéutico , Bovinos , Recuento de Colonia Microbiana , Escherichia coli/efectos de los fármacos , Femenino , Indoles/síntesis química , Indoles/farmacología , Klebsiella pneumoniae/efectos de los fármacos , Mastitis Bovina/microbiología , Pruebas de Sensibilidad Microbiana , Especificidad de la Especie , Staphylococcus aureus/efectos de los fármacosRESUMEN
The calcium complexation and acid-base properties of α-d-isosaccharinate (Isa-) in neutral and in (hyper)alkaline solutions have been investigated via potentiometric titrations, multinuclear NMR, ESI-MS and quantum chemical calculations. Isa- is the primary alkaline degradation product of cellulose, and may be present in radioactive waste repositories and therefore, it could contribute to the mobilization of radioactive nuclei. Because of its limited availability, d-gluconate (Gluc-) is commonly used as a structural and functional model of Isa-. Therefore, the thermodynamic and structural data obtained for Isa- were compared with those of Gluc-. The formation constants of the CaIsa+ and CaGluc+ complexes present in neutral solutions are practically identical, but the binding sites are in different positions and the CaIsa20 solution species cannot be detected. The stepwise formation constant of the CaIsaH-10 complex (forming in alkaline medium) is somewhat larger than that of CaGlucH-10, which is in line with the observation that IsaH-12- is a stronger base than GlucH-12-. The most striking difference is that, unlike Gluc-, Isa- does not form polynuclear complexes with Ca2+. The structural reason for this is that the alcoholate groups on C2 and C3 adjacent to the carboxylate moiety on Gluc- are able to simultaneously bind Ca2+, making the formation of polynuclear Ca-complexes possible. On Isa-, only the alcoholate on C2 is involved, while the other one on C6 is not (supposedly for steric reasons). In conclusion, during the interactions of Gluc- and Isa- with Ca2+, differences rather than similarities prevail.