CaltechTHESIS
  A Caltech Library Service

Mechanisms of indirect mineral reduction by bacteria

Citation

Hernandez, Maria Eugenia (2004) Mechanisms of indirect mineral reduction by bacteria. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-06042004-011242

Abstract

This thesis concerns the biological process of iron reduction mediated by microbially produced extracellular redox-active organic molecules. Two different iron reducing bacteria were studied: Shewanella oneidensis and Pseudomonas chlororaphis. S. oneidensis can grow by reducing ferric iron [Fe(III)] as a terminal electron acceptor in anaerobic respiration (i.e. dissimilatory iron reduction). Previous studies had suggested that it produces extracellular electron shuttles as a strategy for reducing poorly crystalline iron (hydr)oxides, however this had not been shown. To investigate this, a new method was developed to measure iron reduction at a distance using Fe-coated porous glass beads. Given this assay, it was shown that Fe(III) reduction at a distance is an active process that requires anaerobic conditions and coincides with biofilm formation. The possibility that S. oneidensis excretes a soluble quinone derived from the menaquinone biosynthetic pathway as a mediator was ruled out, but it was shown that such molecules are present in culture fluids and can be used by the cells to make menaquinone. Regardless of the nature of the mediator, it appears to act locally within the biofilm-bead environment for S. oneidensis. P. chlororaphis is a plant root isolate that cannot respire iron but produces redox active secondary metabolites (e.g. phenazine carboxamide, PCN) that promote microbial mineral reduction. P. chlororaphis can reductively dissolve poorly crystalline iron and manganese oxides whereas a mutant in one of the phenazine biosynthetic genes (phzB) cannot. PCN functions as an electron shuttle rather than an iron chelator. Multiple phenazines and the glycopeptidic antibiotic, bleomycin, can also stimulate mineral reduction by S. oneidensis MR-1. Because diverse bacterial strains that cannot grow on iron can reduce phenazines, and thermodynamic calculations suggest that phenazines have lower redox potentials than poorly crystalline iron (hydr)oxides in a range of relevant environmental pH (5 to 9), it seems likely that natural products like phenazines promote microbial mineral reduction in the environment. Whether cycling of microbially produced extracellular redox-active organic molecules serves a physiological function remains to be determined.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:DIRB; extracellular electron transfer; mineral respiration; phenazines; shuttles
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Environmental Science and Engineering
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Newman, Dianne K.
Thesis Committee:
  • Newman, Dianne K. (chair)
  • Leadbetter, Jared R.
  • Simon, Melvin I.
  • Hoffmann, Michael R.
Defense Date:18 May 2004
Author Email:mariu.hernandez (AT) gmail.com
Record Number:CaltechETD:etd-06042004-011242
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-06042004-011242
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2433
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:04 Jun 2004
Last Modified:26 Dec 2012 02:51

Thesis Files

[img] PDF (01_Title.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

49Kb
[img] PDF (02_dedicatoria.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

26Kb
[img] PDF (03_Ack_Abst_Index.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

111Kb
[img] PDF (04_Chapter1.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

94Kb
[img] PDF (05_Chapter2.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

228Kb
[img] PDF (06_Chapter3.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

424Kb
[img] PDF (07_Chapter4.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

204Kb
[img] PDF (08_Chapter5.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

356Kb
[img] PDF (09_Chapter6.pdf) - Final Version
Restricted to Caltech community only
See Usage Policy.

91Kb

Repository Staff Only: item control page