Identification and structural characterization of siderophores produced by halophilic and alkaliphilic bacteria

by 1976- Richards, Abigail Marie

By Abigail Marie Richards, Ph. D. Washington State University August 2007 Chair: Brent M. Peyton The first two chapters of the present dissertation focus on a description of two main topics. The first addresses siderophore production by plants and microbes as a means of acquiring ferric iron. Also described is the ability of siderophores to coordinate metals other than ferric iron, such as heavy metals and radionuclides, which potentially alters their speciation and mobility. The second chapter give an overview of the biology of halophilic and alkaliphilic microorganisms. The third part of this dissertation involves the identification and characterization of siderophores produced by the halophilic and alkaliphilic bacterium Halomonas campisalis. Several desferrioxamine siderophores including desferrioxamines G1, G1t, X3, X7, D2, and E were isolated from low-iron, culture supernatant and structurally characterized by ESI-MS and ESI- MS/MS. This work represents the first documentation of ferrioxamine production by a haloalkaliphilic bacterium. v The fourth part of this dissertation is an assessment of siderophore production in a naturally saline and alkaline environment, the soda lake Soap Lake, located in eastern Washington State, USA. Eight siderophore producing halo-alkaliphiles were isolated from Soap Lake. Of these isolates, several were found to belong to the genus Halomonas. The isolate SL28, most closely related to Halomonas pantelleriense, was found to produce a new family of six of amphiphilic siderophores, named the sodachelins. The sodachelin siderophores are of particular interest because, when exposed to UV light, they facilitate a photolytic reduction of Fe(III) to Fe(II) along with a cleavage of the ligand located at the ?-hydroxyaspartate residue. To my knowledge, this is the first characterization of amphiphilic siderophores produced by a bacterium from a soda lake environment that is capable of reducing Fe(III). The final portion of this dissertation contains suggestions for future work. Much of this work focuses on the identification of the siderophores produced by other halophilic and alkaliphilic isolates obtained in an earlier portion of this work. Siderophore production in haloalkaliphiles (and extremophiles in general) is poorly characterized and some of the isolates appear to produce siderophores that may constitute new compounds. vi