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Bacterial strain Burkholderia contaminans MS14 was isolated from soil that suppressed brown patch disease of lawn grass. An antifungal compound was purified from the liquid culture of this bacterium. In this study, complete covalent structures of two purified closely related antifungal compounds were determined by the experiments of TOCSY, NOESY, ROESY, 13C HSQC 2D NMR, and ESI-MS and GC. The analysis of monoisotopic masses of the purified preparation indicated the presence of two related compounds with masses determined to be 1199.543 and 1215.518 Da; the difference corresponds to the mass of an oxygen atom. GC analysis identified a xylose sugar attached to the antifungal compound. NMR experiments revealed that the compound is cyclic and composed of eight amino acids, two of which are beta-hydroxy derivatives of Tyr and Asn, and one being a novel amino acid. The novel amino acid serves as the scaffold for the attachment of the xylose and a short acyl chain. The spectrum and concentration of antifungal activity were determined using a microtiter plate assay. The antifungal compound demonstrated potent antifungal activities against a broad panel of fungal plant and animal pathogens, as well as two Pythium spp. Microscopic observations showed that the antifungal compound disrupts normal membrane morphology. The cells fill with large inclusion bodies and the membrane becomes irregularly shaped and swollen following the exposure to subinhibitory concentrations of the antifungal compound. Our data support the identification of a novel fungicide and the compound has been named occidiofungin, meaning fungal killer.

NCBI PubMed ID: 19673482
Publication DOI: 10.1021/bi900814c
Journal NLM ID: 0370623
Publisher: American Chemical Society
Correspondence: Smith L
Institutions: Mississippi State University, Department of Entomology and Department of Plant Pathology, Mississippi, USA, University of Alabama at Birmingham, Department of Microbiology, Birmingham, USA, Mississippi State University, College of Veterinary Medicine, Department of Pathobiology and Population Medicine, Mississippi, USA, Mississippi State University, Department of Biological Sciences, Mississippi, USA, University of Alabama at Birmingham, Comprehensive Cancer Center Mass Spectrometry Shared Facility, Birmingham, USA, University of Wisconsin-Madison, National Magnetic Resonance Facility at Madison (NMRFAM), Madison, USA
Methods: 13C NMR, 1H NMR, methylation, NMR-2D, ESI-MS, acid hydrolysis, GLC, MS/MS, biological assays, cell growth, antifungal activity assay

In extracts prepared from various fruits as well as in fruit juices a single tryptophan glycoconjugate was detected by HPLC-MS analysis. Product ion spectra demonstrated the N-glycosidic linkage of a hexose moiety to the indole nitrogen. For structure elucidation, the novel tryptophan glycoside was isolated from pear juice and identified as N(1)-(β-D-glucopyranosyl-(4)C(1))-L-tryptophan by (1)H, HH-COSY and (13)C NMR spectroscopy. Finally, we disclosed the biosynthetic origin of the novel tryptophan metabolite by demonstrating the enzymatic glycosylation of deuterium-labeled tryptophan, which was applied to pear fruit.

biosynthesis, Electrospray Ionization, HPLC-MS/MS, tryptophan-N-glucoside

NCBI PubMed ID: 11052755
Publication DOI: 10.1021/jf0003146
Journal NLM ID: 0374755
Publisher: American Chemical Society
Correspondence: mherderi@pzlc.uni-wuerzburg.de
Institutions: Lehrstuhl für Lebensmittelchemie, Universität Würzburg, Würzburg, Germany
Methods: 13C NMR, 1H NMR, ESI-MS, UV, optical rotation measurement, CID-MS, CD, isotopic labeling, HR-ESI-MS, centrifugation, COSY, HPLC-ESI-MS/MS