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Mechanisms for Extracellular Electron Exchange by Geobacter Species University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations Dissertations and Theses Spring March 2015 Mechanisms for Extracellular Electron Exchange by Geobacter Species Jessica A. Smith University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_2 Part of the Environmental Microbiology and Microbial Ecology Commons, and the Microbial Physiology Commons Recommended Citation Smith, Jessica A., "Mechanisms for Extracellular Electron Exchange by Geobacter Species" (2015). Doctoral Dissertations. 325. https://doi.org/10.7275/6457832.0 https://scholarworks.umass.edu/dissertations_2/325 This Open Access Dissertation is brought to you for free and open access by the Dissertations and Theses at ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. MECHANISMS FOR EXTRACELLULAR ELECTRON EXCHANGE BY GEOBACTER SPECIES A Dissertation Presented by JESSICA AMBER SMITH Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY February 2015 Department of Microbiology © Copyright by Jessica Amber Smith 2015 All Rights Reserved MECHANISMS FOR EXTRACELLULAR ELECTRON EXCHANGE BY GEOBACTER SPECIES A Dissertation Presented by JESSICA AMBER SMITH Approved as to style and content by: ________________________________ Derek R. Lovley, Chair ________________________________ James F. Holden, Member ________________________________ Steven J. Sandler, Member ________________________________ Dawn E. Holmes, Member ____________________________ John M. Lopes, Department Head Department of Microbiology ACKNOWLEDGMENTS I would like to thank my advisor, Derek Lovley, and the members of my committee, James Holden, Steven Sandler, and Dawn Holmes, for supporting and guiding my projects. I especially thank Dawn Holmes for all of her support, advice, and friendship. Without her I truly wouldn’t be where I am today. I also thank Carla Risso and Pier-Luc Tremblay for their invaluable training and mentorship, and not giving up on me. I thank all of the past and current members of the Lovley lab, and all of my co- authors. Above all, thanks to my family, particularly my sister Ashley Smith, who was forever there to make me smile. And to my parents, Willard and Christine Smith, who always support my decisions in life, and encourage me to pursue my goals. iv ABSTRACT MECHANISMS FOR EXTRACELLULAR ELECTRON EXCHANGE BY GEOBACTER SPECIES FEBRUARY 2015 JESSICA AMBER SMITH B.S., WESTERN NEW ENGLAND UNIVERSITY Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Derek R. Lovley Understanding the mechanisms for microbial extracellular electron exchange are of interest because these processes play an important role in the biogeochemical cycles of both modern and ancient environments, development of bioenergy strategies, as well as for bioremediation applications. Only a handful of microorganisms are capable of extracellular electron exchange, one of the most thoroughly studied being the Geobacter species. Geobacter species are often the predominant Fe(III) reducing microorganisms in many soils and sediments, can exchange electrons directly via interspecies electron transfer, and can both donate or accept electrons with a wide variety of extracellular substrates including the electrode of a microbial fuel cell. This dissertation describes three research projects that aim to further understand these mechanisms and identify novel components involved in extracellular electron exchange by Geobacter species. The first uncovers components involved in extracellular electron transfer to insoluble Fe(III) oxides by Geobacter metallireducens. This project identified six c-type cytochromes, a NHL-repeat containing protein, and a gene v potentially involved in pili glycosylation that were essential for reduction of insoluble Fe(III) oxide, but not for soluble Fe(III) citrate. The second research project serves to reveal and examine PilA-pili independent mechanisms for extracellular electron transfer to Fe(III) oxides by Geobacter sulfurreducens. During the course of this study a pilA-deficient strain of G. sulfurreducens adapted to reduce Fe(III) oxide via production of the c-type cytochrome PgcA, which was released into the culture medium, and was required for the newly adapted mechanism of Fe(III) oxide reduction. The third research project investigates the mechanism(s) utilized by G. sulfurreducens for extracellular electron exchange into the cell via the oxidation of the humic substance analog anthrahydroquinone-2,6-disulfonate (AHQDS) in cocultures with G. metallireducens. Cocultures initiated with strains of G. sulfurreducens deficient in genes for proteins previously identified to be important in extracellular electron exchange grew as well as the wild type strain, suggesting that mechanisms for exchanging electrons with extracellular electron donors are substantially different than for reduction of extracellular electron acceptors. vi TABLE OF CONTENTS Page ACKNOWLEDGMENTS .................................................. .............................................. iv ABSTRACT ....................................................................... .............................................. v LIST OF TABLES ............................................................. .............................................. ix LIST OF FIGURES ............................................................ .............................................. x CHAPTER 1. INTRODUCTION .......................................................... .............................................. 1 1.1 Central Objectives and Goals ........................................................................... 1 1.2 Organization of the Dissertation ....................................................................... 2 1.3 Extracellular Electron Exchange ....................................................................... 2 1.3.1 Extracellular Electron Acceptors ..................................................... 3 1.3.1.1 Dissimilatory Metal Reduction ............................................ 4 1.3.1.2 Humic Substances and Other Extracellular Quinones .......... 9 1.3.1.3 Microbial Fuel Cells as Electron Acceptors ......................... 10 1.3.1.4 Extracellular Interspecies Electron Transfer ......................... 12 1.3.2 Extracellular Electron Donors ......................................................... 15 1.3.2.1 Environmental Compounds ................................................. 16 1.3.2.2 Microbial Fuel Cells as Electron Donors.............................. 18 1.3.2.3 Direct Interspecies Electron Exchange ................................. 19 1.4 Extracellular Electron Exchange by Geobacter species..................................... 20 1.4.1 Cytochromes ................................................................................... 22 1.4.2 Microbial Nanowires....................................................................... 26 1.4.3 Exopolysaccharides......................................................................... 28 1. OUTER CELL SURFACE COMPONENTS ESSENTIAL FOR FE(III) OXIDE REDUCTION BY GEOBACTER METALLIREDUCENS ....................................... 30 2.1 Abstract ............................................................................................................ 30 2.2 Introduction ...................................................................................................... 31 2.3 Materials and Methods ..................................................................................... 33 vii 2.4 Results and Discussion ..................................................................................... 37 2.5 Implications ..................................................................................................... 45 2. GOING WIRELESS: FE(III) OXIDE REDUCTION WITHOUT PILI BY GEOBACTER SULFURREDUCENS STRAIN JS-1 ............................................... 52 3.1 Abstract ............................................................................................................ 52 3.2 Introduction ...................................................................................................... 53 3.3 Materials and Methods ..................................................................................... 56 3.4 Results and Discussion ..................................................................................... 62 3.5 Implications ..................................................................................................... 67 3. SYNTROPHIC GROWTH VIA QUINONE-MEDIATED INTERSPECIES ELECTRON TRANSFER ...................................................................................... 79 4.1 Abstract ............................................................................................................ 79 4.2 Introduction ...................................................................................................... 80 4.3 Materials and Methods ..................................................................................... 83 4.4 Results and Discussion ..................................................................................... 85 4.5 Implications ....................................................................................................
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