Soap Lake, located in Washington State, is a naturally occurring saline and alkaline lake. Several organisms inhabiting this lake have been identified as producers of siderophores that are unique in structure. Bacterial isolates, enriched from Soap Lake sediment and water samples, were screened for siderophore production using both the chrome azurol S (CAS) agar plate and liquid methods. Bacterial isolate Halomonas sp. SL01 was found to produce relatively high concentrations of siderophores in liquid medium (up to 40 µM). Siderophores from the isolate were separated from the culture supernatant using solid phase extraction and purified by high-performance liquid chromatography (HPLC). Siderophore structure was determined using LC/MS/MS (liquid chromatography/mass spectrometry/mass spectrometry) and fatty acid methyl ester (FAME) GC. Two distinct new families of amphiphilic siderophores were produced by isolate SL01. All siderophores ranged in size from 989 to 1096 atomic mass units and consisted of a conserved peptidic head group (per family), which coordinates iron, coupled to fatty acid moieties. The fatty acyl moieties were C10-C14 in length and some with hydroxyl substitutions at the third α position. These siderophores resembled amphiphilic aquachelin siderophores produced by Halomonas aquamarina strain DS40M3, a marine bacterium as well as siderophores from isolate Halomonas sp. SL28 that was found to produce amphiphilic siderophores. Bacteria thriving under saline and alkaline conditions are capable of producing unique siderophores resembling those produced by microbes inhabiting marine environments.

Soap Lake, located in Washington State, is a meromictic soda lake which was the subject of a prior NSF funded Microbial Observatory. Several organisms inhabiting this lake have been identified as producers of siderophores that are unique in structure. Two isolates found to be of the species Halomonas, SL01 and SL28 were found to produce suites of amphiphilic siderophores consisting of a peptidic head-group, which binds iron appended to fatty acid moieties of various lengths. The ability for siderophores to self-assemble into vesicles was determined for three suites of amphiphilic siderophores of unique structure (two from SL01 and one from SL28). These siderophores resemble the amphiphilic aquachelin siderophores produced by Halomonas aquamarina strain DS40M3, a marine bacterium. Vesicle self-assembly studies were performed by dynamic light scattering (DLS) and epifluorescence microscopy. The addition of ferric iron (Fe +3 ) at different equivalents, where an equivalence of iron is defined as equal to the molarity of the siderophore, demonstrated vesicle formation. This was suggested by both DLS and epifluorescence microscopy. Bacteria thriving under saline and alkaline conditions are capable of producing unique siderophores that self-assemble in micelles and vesicles due to ferric iron chelation. (186 words) Iron is an important mineral for nearly all living organisms, and bacteria have developed siderophores for its uptake. Siderophores are low molecular weight compounds that specifically coordinate ferric iron. In addition to siderophores, metal chelation can occur through different molecules, like cardiolipins and phosphatidylserine which bind ferric iron and manganese. 1 While specific for the coordination of iron, some siderophores can form stable complexes with other metal ions. Examples include the chelation of uranium (VI) by deferrioxamine B and pyochelins. 2, 3 Other researchers have demonstrated neptunium (V) and boron chelation. 4, 5 Some siderophores are amphiphilic, which means the molecule has both hydrophilic and hydrophobic properties. Amphiphilic siderophores form micelles above a threshold concentration and are shown to self-assemble into vesicles when excess ferric iron is chelated. 6-8 The self-assembly in amphiphilic siderophores was first described by Martinez and co-workers (2000). 8 Those physicochemical properties confer upon siderophores the potential to form micelles in their deferrated form, when over their critical micelle concentration (cmc), which in marinobactins and aquachelins is about 25 to 150 µM. Trends of higher cmc are expected when siderophores are ferrated. Micelle-to-vesicle transitions for marinobactin E, yielding vesicles of approximately 140 to 180 nm in size was shown via dynamic light scattering (DLS). 8 Because the diameter of micelles formed by siderophores is near the limit of detection of DLS, other methods are typically used to determine their size. For example, small-angle neutron scattering (SANS) in combination with DLS has been used to account for micelle ...