Browsing by Subject "Cytochromes"

Now showing 1 - 2 of 2
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    Identification of extracellular matrix components essential for a conductive Geobacter sulfurreducens biofilm
    (2011-11) Rollefson, Janet Beth
    Electron transfer from Geobacter sulfurreducens cells to electrodes or metal oxides requires proper expression and localization of redox-active proteins as well as attachment mechanisms that interface bacteria with surfaces and other cells. Type IV pili and c-type cytochromes have long been considered important components of this conductive network. In this work, a large-scale mutagenesis of G. sulfurreducens was performed and mutants were screened for extracellular electron transfer and attachment phenotypes, identifying new genes essential for a conductive Geobacter network. A mutant defective in polysaccharide export to the extracellular matrix (Δ1501, ΔxapD::kan) was identified based on its altered surface attachment. Characterization of this mutant revealed the importance of extracellular polysaccharides for proper attachment and anchoring of the external c-type cytochromes necessary for a conductive biofilm network. Furthermore, decreased polysaccharide content was found in commonly studied cytochrome and type IV pili mutants, with defects in cell to cell and cell to surface attachment correlating with levels of extracellular polysaccharides. The extracellular matrix of G. sulfurreducens is therefore a complex network of polysaccharides, type IV pili, and c-type cytochromes. Disruption of any one of these extracellular components alters overall matrix properties and impedes extracellular electron transfer and attachment.
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    Metal reduction by Geothrix fermentans
    (2013-08) Mehta, Misha Girish
    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.