A rapid and sensitive paper electrophoresis assay for the detection of microbial siderophores elicited in solid-plating culture.

A rapid and sensitive assay for the detection of microbial siderophores (iron-binding compounds) is described. Nine representative fungal and bacterial cultures including Ustilago sphaerogena, Penicillium sp., Fusarium roseum, Rhodotorula pilimanae, Bacillus subtilis W 23, Bacillus subtilis W 168, Bacillus megaterium, Azotobacter vinelandii OP, and Escherichia coli B, were nutritionally stressed for iron by sequential transfers on iron-deficient solid-plating media. In response to Fe-stress conditions, the microorganisms excreted siderophore compounds into the extracellular solid culture medium. The solid agar matrix effectively concentrated and restricted the migration of the siderophore compounds to the region immediately adjacent to colonial growth. Agar-block samples from this region were removed and placed at the origin of an electrophoresis paper strip. The resultant absorbed material from the agar-block sample was subjected to high-voltage paper electrophoresis which separated the siderophore compounds by size and molecular net charge. Phenolic acid ("catechol")-type siderophores were detected by fluorescence under uv light. Hydroxamic acid-type siderophores were visualized by spraying the electrophoretogram with ferric iron solution.