(Santa Barbara, Calif.) Structures of newly-discovered siderophores (the iron-carrying molecules secreted by bacteria to facilitate iron acquisition) described in the February 18 issue of Science by researchers at the University of California, Santa Barbara and other institutions, shed light on how marine bacteria acquire iron and raise provocative questions about the evolution of iron uptake by marine bacteria.

All bacteria need iron to grow, and in the ocean there is very little iron, explained Alison Butler, professor of chemistry and biochemistry at UC, Santa Barbara and co-author of the article. "We wanted to know what molecular mechanisms control iron uptake," said Butler.

The article, "Self-Assembling Amphiphilic Siderophores from Marine Bacteria," describes the structures of the marinobactin and aquachelin siderophores which have polar peptidic head groups and hydrophobic fatty acid tails, explained Butler. "They have a hydrophobic portion and a hydrophilic portion," she said. "Like soap, they have a portion that dissolves in water and part that dissolves in grease."

The marinobactins are present as micelles (aggregations of molecules) and upon addition of iron, the micelles undergo a spontaneous phase change to form vesicles (bladder-like spheres).

When iron is added, it binds to the peptidic head, and then vesicles are formed.

"The transformation from micelle to vesicle upon iron coordination is the first example, to our knowledge, of such a metal-induced phase change in a biologically produced compound," said the authors. "The presence of this metal-induced switch raises questions about the physiological role for this transformation."

The authors were struck by the fact that different bacteria had the same 'strategy' for acquiring the iron. They state: "It is quite striking that these siderophores, whose distinctive properties hint at the possibility of a novel iron acquisition mechanism, are made by strains from two differen
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Contact: Gail Brown
gbrown@instadv.ucsb.edu
805-893-7220
University of California - Santa Barbara
16-Feb-2000