Identifying Genes with Roles in Power Output of Exoelectrogenic Bacteria in Microbial Fuel Cells
David Thompson Secondary
Floor Location : S 225 E
This project aims to uncover new insights into the genes driving microbial electron-transfer in microbial fuel cells (MFCs). Although the design and operation of MFCs are fairly advanced, our current understanding of the biological functions driving the mechanisms of electricity generation is lacking.
In this study, a novel procedure was utilized to identify genes with roles in power output of exoelectrogenic bacteria in microbial fuel cells (MFCs). An E. coli fosmid library constructed from microorganisms in a bioreactor fed with metal-contaminated water was incubated in dual-chambered, batch operated MFCs. The MFCs utilized carbon cloth electrodes with a Nafion N117 membrane as the proton exchange membrane (PEM) and potassium ferricyanide as the electron sink. Cell voltage was recorded continuously across a 1000 ohm resistor. Samples from the anode of the MFCs were occasionally drawn out to conduct OD660 readings. MFC performance was ascertained by conducting potentiostatic discharges using a potentiostat.
The MFCs incubated with the fosmid clones performed significantly better than the MFCs incubated with a E. coli DH5? control strain, generating almost 5 times more peak power during a 48 hour incubation period. OD660 tests suggest that the abundance of bacteria in the anolyte do not affect the power generation properties of the MFCs. Polarization and power curves reveal improved potential and power generation of the MFCs incubated with the fosmid clones at mid to high current ranges compared to the MFCs incubated with E. coli DH5?. This suggests that the fosmid clones may carry genes that improve biofilm formation and structure, or encode for the biosynthesis of natural electron mediators that decrease the ionic resistance of the biofilm or electrolyte. These inferences are supported by the lower internal resistances of the MFCs incubated with fosmid clones compared to that of the control. The results of this study demonstrate that bacteria found in mine-remediation bioreactors may be suitable for the role of electricity generation in MFC systems, and that using a gain of function approach to rapidly screen a wide array of genes in gene libraries may be an efficient, and feasible method to identify genes that enhance power generation of exoelectrogenic microbes in MFCs.
Analysis of the relative abundances of the fosmid inserts in the MFCs is currently being conducted. Samples taken from the biofilm in the MFCs will be plated on LB-Agar. Individual colony forming units (CFUs) will be extracted into respective wells of LB. The relative abundances of the inserts will be ascertained using restriction enzyme fragment length polymorphism. Inserts with the highest relative abundances will be sequenced using Sanger sequencing.
Such insights into the mechanisms of power generation may to better understanding of the mechanics behind electron-transfer in microorganisms, and may lead to improved MFC reactor designs.