Chemical properties and NMR spectroscopic identification of certain fungal siderophores

Abstract

Siderophores of six fungi <i>viz. Aspergillus </i>sp. ABp4, <i>Aureobacidium pullulans, Penicillium oxalicum</i>,<i> P. chrysosporium</i>, <i>Mycotypha africana </i>and <i>Syncephalastrum racemosum </i>were examined for their (1) electrophoretic<i> </i>mobilities to determine the acidic, basic or neutral charge; (2) Fe (III) binding nature <i>viz., </i>mono-, di-, or trihydroxamate; (3)<i> </i>amino acid composition; and (4) NMR (nuclear magnetic resonance) spectroscopy to determine their structure.<i> </i>Electrophoretic mobilities of siderophores of 3 fungi (<i>P. oxalicum, P. chrysosporium, </i>and <i>M. africana</i>)<i> </i>exhibited net basic<i> </i>charge, siderophores of 2 fungi (<i>Aspergillus </i>sp. ABp4 and <i>S</i>. <i>racemosum) </i>were acidic and 1 fungus (<i>A. pullulans) </i>was

neutral. Electrophoresis of ferrated siderophore at <i>p</i>H<i> </i>2 and colour of the spots indicated that siderophores of <i>Aspergillus </i>sp. ABp4 and <i>P. oxalicum </i>and <i>A. pullulans </i>were trihydroxamates, whereas siderophore of <i>P. chrysosporium </i>was dihydroxamate. Amino acid composition of siderophores purified by XAD-2 column chromatography, revealed the presence of asparagine, histidine, and proline in <i>Aspergillus </i>sp. ABp4, serine and alanine in <i>P. chrysosporium, </i>and valine in <i>M. africana. </i>The structure of purified siderophores as revealed by NMR spectroscopy identified siderophore of AB – 2670 (<i>A. pullulans</i>) as asperchrome F1, and AB-513 (<i>M. africana</i>)<i> </i>as rhizoferrin. The peak obtained for siderophore AB-5 (<i>Aspergillus </i>sp. ABp4) did not show resemblance to any known siderophore, therefore may be an exception.