Iron is required for growth of nearly all microorganisms. While iron is the fourth most abundant element on the earth’s surface, iron is only sparingly soluble in the aerobic, near neutral conditions under which most microorganisms grow. Therefore, microorganisms experience iron limitation in nearly every environment where they grow, from infection of a mammalian host (where iron is highly controlled by protein complexation) to aquatic and marine environments (where iron is relatively insoluble or is complexed by organic ligands). Bacteria, fungi, and other microbes have developed complex strategies to compete for iron under these conditions. Specifically, many microbes produce low molecular weight, iron binding compounds called siderophores to acquire iron from the environment. Siderophores are secreted by microorganisms and then are taken back into the cells as the ferric complex to promote microbial growth.
The siderophores produced by marine α-proteobacterium Ochrobactrum sp. SP18 were structurally characterized. This marine bacterium produces a suite of three aerobactin-derived, amphiphilic siderophores composed of citrate, symmetrically derivatized with L-lysine which is N-hydroxylated and N-acylated to form two hydroxamate binding groups. Each siderophore contains one (E)-2-decenoic acid moiety and an (E)-2-octenoic, octanoic, or (E)-2-decenoic acid moiety. The photoreactivity and membrane affinity of these siderophores were investigated.
In addition to isolation of the cell-associated ochrobactin siderophores from the marine α-proteobacterium Ochrobactrum sp. SP18, these amphiphilic siderophores were isolated from the marine γ-proteobacterium Vibrio sp. DS40M5. The isolation of these siderophores from two widely different strains, that are in distinct clades of bacteria suggests that these siderophores may be widely utilized in marine environments.