Microbial Fuel Cells (MFCs) are bio-electrochemical systems that exploit the ability of electro-active microorganisms to colonise an electrode, breakdown organic material and donate electrons to the electrode as part of anaerobic respiration (see Figure). MFCs typically comprise an anode electrode and a cathode electrode separated by a cation exchange membrane. The membrane employed in MFCs is usually non-porous and facilitates the transfer of cations whilst maintaining physical separation between the anode and cathode half-cells.
The EVOBLISS project will allow the study of microbial evolution over time, with energy generation as the primary selective pressure. Different types of 3D fabricated substrata will be utilised as MFCs, which will allow the microbial communities to directly transfer electricity on electrodes inside these units. The electricity generated is directly proportional to the rate of growth and metabolism of the microbes, and an essential respiratory pathway.
In other words, the higher the electrical output, the faster the microbes will be growing, and the healthier the microbial community will be. Using electricity as the selective pressure will optimise communities into being more efficient at electron transfer, when fed with different feedstocks. The validation of this line of empirical experiments will ultimately be the inoculation of existing MFCs which are currently being used for powering systems (e.g. EcoBots, pumps, LEDs, mobile phones), to demonstrate the improvement in performance achieved from the evolutionary selected microbial communities.
The signal output of the MFC is the sum of a huge number of metabolic processes occurring within the microbial community. These processes can all be positively or negatively affected by other pressures occurring within the MFC. For example, the pH within the anode chamber will be optimal for some micro-organisms and sub-optimal for others, including electro-active organisms, therefore pH will be an important parameter for the Evobot to control and produce optimum power output from the MFC. Other selective pressures affecting the MFC anode include the type and concentration of food substrates such tryptone/yeast extract, acetone, cellulose that support the community.