Determination of critical micelle concentration of an amphiphilic siderophore

Abstract

The sodachelins are a group of six amphiphilic siderophores produced by a halophilic bacterium. Amphiphilic siderophores, such as the sodachelins, are important in the solubilization and sequestration of iron related to microbial metabolism and are also unique in their ability to form micelle and vesicular structures. This professional paper describes siderophore importance in iron bioavailability, siderophore chemistry and biological function and a thermodynamic analysis of forces that drive micellization and vesicle formation. A description of experiments conducted to isolate, separate and purify the sodachelins for the purpose of measuring their critical micelle concentration (CMC) follows the review of literature. Initial siderophore isolation was achieved using XAD-2 resin to generate a crude extract. This crude extract was then purified by HPLC, and the measurement of CMC of a single siderophore, sodachelin E, was performed with a tensiomat instrument. Crude separation by XAD resin was proven successful; XAD resin has a strong affinity for siderophores as shown by experiment with the siderophore desferrioxamine B (DFB) as a control. Purification of the crude siderophore extract by only one pass on the HPLC was proven insufficient to generate a single, pure siderophore. At least a second pass on the HPLC is required to remove all contaminants. The protocol developed for CMC analysis is consistent and accurate based on a sodium dodecyl sulfate (SDS) control experiment. An approximate CMC value of 140 micron for sodachelin E was obtained, however, HPLC analysis showed contamination of another sodachelin and possible other organic solutes, indicating that this value may be inaccurate.