The growing need for alternative fuel sources has sparked interest and research across many scientific and engineering disciplines. The fledgling field of microbial fuel cell development has previously relied on anaerobic metal reducing organisms such as Geobacter sulfurreduccens. This project sought to isolate genes from the electron shuttling pathway in Geobacter and transform them into the more manageable aerobic Escherichia coli. The Missouri University of Science and Technology iGEM team isolated four outer membrane cytochrome (omc) genes from Geobacter, vital to the extracellular transportation of electrons. The four genes; omcB, omcE, omcS and omcT, were cloned into individual plasmids. The eventual goal is to combine all four genes into one plasmid to transform into E. coli to create an aerobic, electron transporting microbial system.
Ringeisen, Bradley R., Ricky Ray, and Brenda Little. “A Miniature Microbial Fuel Cell Operating with an Aerobic Anode Chamber.” Science Direct 165 (2007):591-97. Online.
What is a Microbial Fuel Cell?
A microbial fuel cell is a device similar to a battery that can harness electricity from bacteria. These exoelectrogenic bacteria transport electrons outside of the cell to reduce compounds in the outside environment. The process is the final step in normal electron transport for these bacteria. Microbial fuel cells harness these extracellular electrons to power a load. The bacteria grown on the anode, where they donate electrons to a carbon surface. The electrons then move along the circuit where the energy is capture to power a lightbulb. Hydrogen ions are transported across a permeable membrane into the cathode where they meet the electrons and finally reduce oxygen into water.
Creating a better MFC
In the past, microbial fuel cell research has been conducted solely in an anaerobic environment due to the anaerobic nature of most exoelectrogenic bacteria. We moved the key electron shuttling genes from an anaerobic bacteria, Geobacter sulfurreducens, to an aerobic bacteria, Escherichia coli, so as to facilitate MFC research in an aerobic environment.
In older, more traditional designs, MFCs have been limited by the surface area of the anode. The bacteria must make contact with the anode so the electrons can be harvested to power a device. In our new designs, we modeled our work after research conducted by Dr. Bradley R. Ringeisen, Ricky Ray, and Brenda Little at the Naval Research Labs in Washington D.C. The goal of the new design is to maximize anode surface area by using high surface area carbon materials and keeping a very large anode to membrane surface area ratio. In the Mini-MFC design, the limiting factor is the membrane surface area and permeability, not the anode surface area.
To create even larger surface areas for the anode we contacted materials specialists at the Leventis Lab at Missouri S&T. We are using glassy carbon aerogels as anode materials instead of the traditional carbon or graphite felt.