Metal reduction by Geothrix fermentans

Abstract

Bacteria with an ability to transfer electrons beyond their outer surface can utilize a variety of insoluble metals in anaerobic respiration. The consequences of these electron transfer reactions directly affect global Fe and Mn biogeochemistry, hydrocarbon cycle and U(VI) bioremediation. The main objective of this work is to understand the mechanism of electron transfer and ecological niche of Geothrix-like Acidobacteria consistently found in subsurface metal-reducing and bioremediating environments. In this thesis a variety of independent approaches were used to examine the mechanism by which Geothrix fermentans reduces Fe(III)-oxides and electrodes was examined in this thesis. The genomes of two Geothrix species were sequenced to identify key functional genes involved in respiration and metabolism. Electrochemical tools, that are now standard methods for characterizing the multi-dimensional aspects of microbial electron transfer, were used to identify the high potential dependent, shuttle-based respiration of G. fermentans. Biochemical characterizations of membrane proteins were performed to understand how electrons generated during intracellular metabolism are relayed across membranes to an extracellular terminal electron acceptor. Decaheme c-type cytochromes were identified and heterologously expressed in mutant strains of the metal-reducing bacterium S. oneidensis MR-1, lacking key proteins required for metal respiration. This research also identified different microbial communities associated with current production in microbial fuel cells. Additionally a genetic technique was optimized in order to identify important genes required for electron transfer by Geobacter sulfurreducens under selective growth conditions.