Chemical investigation of the transformation of the crucifer phytoalexins brassinin, brassilexin and camalexin by the phytopathogenic fungus <i>Alternaria brassicicola</i> was carried out. The objectives of this study included:<p> 1) the isolation and characterization of the metabolites of biotransformation of brassinin, brassilexin and camalexin by <i>A. brassicicola</i>;<p> 2) determination of the antifungal activity of these phytoalexins and their metabolites against <i>A. brassicicola.</i><p> The phytoalexins were synthesized and characterized using HPLC retention time tR, 1H NMR, 13C NMR, LC-MS and HRMS-ESI data. The metabolites of the biotransformation were also synthesized and characterized similarly. The metabolism of each phytoalexin and their metabolites was studied by analyzing broth extracts by HPLC. The percent inhibition of growth of <i>A. brassicicola</i> was determined by radial growth mycelial assays.<p> The biotransformation of brassinin by <i>A. brassicicola</i> afforded Nb-acetyl-3-indolylmethylamine via indole-3-methylamine intermediate. Brassilexin was metabolized to 3-(amino)methyleneindoline-2-thione by the reduction of the isothiazole ring. Camalexin did not appear to be metabolized or the metabolism was very slow. The results of biotransformation and bioassay studies established that the metabolism of brassinin by <i>A. brassicicola</i> was a detoxification process. However, these studies using brassilexin did not provide a rigorous conclusion. Camalexin showed strong inhibition of growth against <i>A. brassicicola</i> suggesting its importance in defense against this pathogen.

Zugl.: Frankfurt (Main), Univ., Diss., 2009

Reproduction de : Thèse de doctorat : Pathologie, Toxicologie, Génétique et Nutrition : Toulouse, INPT : 2008. / Titre provenant de l'écran-titre. Bibliogr. 322 réf.

Reproduction de : Thèse de doctorat : Qualité et sécurité des aliments : Toulouse, INPT : 2006. / Titre provenant de l'écran-titre. Bibliogr. 165 réf.

Thèse de doctorat : Biologie médicale : Strasbourg 1 : 2006. / Titre provenant de l'écran-titre. Bibliogr. p. 142-163.

Reproduction de : Thèse de doctorat : Sciences des procédés : Toulouse, INPT : 2005. / Titre provenant de l'écran-titre. Bibliogr. 233 réf.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 80-94.

Thesis (doctoral)--Christian-Albrechts-Universität zu Kiel, 1998.

Carvone is a flavor and fragrance compound that is prominent in nature and is found in the essential oils of many plants. Carvone exists as two enantiomers, (R)-(-)-carvone which has a spearmint aroma and (S)-(+)-carvone which has a caraway aroma and can be used in a variety of applications: as a common food additive, as an antimicrobial/antifungal agent and as a potato sprout inhibitor. Carvone is currently produced by the extraction of essential oils from plants where the yield and quality of the extracted oil depends largely on successful agricultural production of dill, spearmint and caraway plants. Biotechnological production can offer a constant supply of carvone that is independent of several agricultural limitations. In this study, it was confirmed that the substrate and product of the microbial biotransformation of trans-carveol to (R)-(-)-carvone by Rhodococcus erythropolis DCL14 can be inhibitory to the cells at high concentrations. As such, a two phase partitioning bioreactor was employed where the function of the second phase (immiscible organic solvent or solid polymer beads) was to partition the inhibitory substrate into the aqueous phase at a rate governed by the metabolic demand of the cells and uptake the inhibitory product as it accumulated in the aqueous phase. Rational selection strategies were employed when determining the appropriate organic solvent and solid polymer to be used as the second phase. The performance of the reactor was evaluated based on volumetric productivity, length of biotransformation and total volume of substrate added to the reactor. The most successful reactor configuration was one in which styrene/butadiene copolymer beads were used as a second phase in the reactor and the fermentation medium was continuously circulated through an external extraction column packed with Hytrel® 8206 polymer beads. The volumetric productivity, length of biotransformation and total volume of substrate added to this reactor were 99 mg/L.h, 48.75 h and 35 mL, respectively whereas in the single phase benchmark reactor the performance indicators were only 31 mg/L.h, 15.25 h and 5 mL, respectively. These results clearly show the advantage of employing a partitioning bioreactor configuration for the biotechnological production of high value chemical species that exhibit cytotoxicity. / Thesis (Master, Chemical Engineering) -- Queen's University, 2008-01-24 10:20:09.589

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