A growing list of Gram-negative iron reducing bacteria are known to be also capable of reducing soluble U(VI) to insoluble U(IV) biologically, providing potential uranium bioremediation strategies. Though model organisms have been studied for years, our knowledge of them is still limited and iron reductases of many other poorly characterized bacteria remain unknown. In this thesis, bottom-up proteomics using iTRAQ labeling was employed to analyze differential protein expression in Anaeromyxobacter dehalogenans 2CP-1, Shewanella oneidensis MR-1, Geobacter sulfurreducens PCA and Geobacter bemidjiensis Bem grown on ferric citrate versus fumarate. In all organisms, there were modest increases in enzymes associated with overall activity (oxidative phosphorylation, TCA cycle, RNA polymerase) - consistent with iron being a more energetic electron acceptor than fumarate. For A. dehalogenans, our analyses suggested which cytochromes are iron reductases (A2cp1_0127 and A2cp1_1731). Additional studies such as heterologous expression or knock out mutations will be needed to prove this function.