Combining electrochemical, -omics, and microscopic approaches to characterize transport limitations in anode-respiring bacteria biofilms
Abstract
Combining electrochemical, -omics, and microscopic approaches to characterize transport limitations in anode-respiring bacteria biofilms César I. Torres, Rosa Krajmalnik-Brown, and Sudeep Popat Anode-respiring bacteria (ARB), such as Geobacter sulfurreducens, have been studied for over a decade for their capability of producing electrical current through metabolic respiration of organic compounds. The electricity produced by ARB can be used for a myriad of applications of interest to the Navy, including powering remote sensors, waste-to-energy technologies, and low power sources based on non-flammable fuels. To date, there is no consensus as to what limits current production by ARB; characterizing the rate-limiting step in current production is extremely important for further improving microbial electrochemical cells. So far, potential and proton (pH) gradients have been documented and studied as possible limitations. Since there are experimental measurements of both gradients present in G. sulfurreducens and other ARB, it is not clear whether one is prevalent over the other or a dual limitation occurs in ARB biofilms. We propose electrochemical, -omics, and microscopic measurements to better characterize electron transport pathways that drive potential gradients in ARB. We will focus on G. sulfurreducens to develop a sound methodology that will later be applied also on Geoalkalibacter ferrihydriticus and Thermincola ferriacetica. The latter ARB have been characterized in our lab using electrochemical techniques, and their genomes have been recently sequenced. We will perform electrochemical measurements as a function of biofilm growth. Both fast-scan CVs and potential steps will be used to determine the current derived from independent respiratory pathways by ARB. These techniques were instrumental in identifying the two pathways used by G. sulfurreducens. Based on these measurements, along with biofilm thickness measurements (confocal microscopy), we can estimate the number of cells utilizing each pathway and the distance from the anode at which this shift occurs. We will further investigate the ARB biofilm using a transcriptomic and proteomic approach. Our first goal is to identify which genes are differentially expressed in each pathway identified in G. sulfurreducens by growing biofilms at different potentials. The genes that are differentially expressed at different potentials will create a baseline for each individual pathway. A small proteomic library targeting only membrane associated proteins can confirm the transcriptomic analysis. We will also expand our proton transport models and its link to electron transport by ARB. To accomplish this Task, pH gradients will be observed in ARB biofilms of G. sulfurreducens and Glk. ferrihydriticus using confocal microscopy and pH sensing dyes. The main goal of these experiments is to develop pH profiles within the anode biofilm as it grows. This will allow us to correlate the current density profile of the growth phase to pH limitations and potential gradients. The proposed work will uncover missing information of the pathways utilized by ARB for anode respiration and will provide a comprehensive understanding of ARB growth and current production limitations. These findings will lead to novel approaches to improve current production and performance of microbial electrochemical systems.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 08, 2016
- Source ID
- N000141512702
Entities
People
- César I. Torres
Organizations
- Arizona State University
- Office of Naval Research
- United States Navy