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Bio-electric Interface
Microbial half fuel cells
Methods
- Fuel cells were constructed using carbon weave electrodes and reference electrodes provided by Matthew Knighton from Dr Bruce Ward’s lab.
- Fuel cells were assembled by using a bottle cap with an attached carbon weave electrode to seal 500 or 250 ml standard glass bottles. The electrodes were attached to the caps using silicone sealant. Bottles were then autoclaved. In sterile conditions, reference electrodes were dipped in alcohol, inserted into the cap of the bottles and sealed with silicon sealant. The half fuel cells were then filled with media, inoculated with bacteria and sealed with parafilm in order to ensure anaerobic growth. The bacteria were left to grow at room temperature. (Figure 1)
- Media used: standard LB or M9 (minimal growth medium) supplemented with 0,4% glycerol or sodium acetate.
- Measurements were obtained using a digital multimeter.
Results
- We have examined the behaviour of S. oneidensis and E. coli in different media using half fuel cells. We managed to obtain results using the following media: LB, M9 with glycerol and M9 with sodium acetate. The results are summarised in figures 2 and 3 below. We also performed a measurement for Citrobacter freundii to see whether it differs from other bacteria.
Figure 1: Our microbial half fuel cells with S. oneidensis and E. coli
Figure 2: Half fuel cells experiments 1 and 2, using LB medium for growth of S. oneidensis and E. coli. Experiment 1 (left) was performed using 500 ml of medium while experiment 2 (right) was performed using 250 ml of medium.
Figure 3: Half fuel cells experiments 3 and 4, using M9 medium for growth of S. oneidensis, E. coli and Citrobacter freundii. Experiment 3 (left) was performed using 250 ml of medium M9 with 0,4% glycerol while experiment 4 (right) was performed using 250 ml of medium M9 with 0,4% sodium acetate. In experiment 4, C. freundii was also tested.
Discussion and conclusions
For the fuel cell experiment we have obtained a series of interesting results. In our half fuel cells, E. coli seemed to exhibit properties similar to S. oneidensis. E. coli generates potential which closely relates to S. oneidensis outputs and the results repeat throughout multiple media, except for the final experiment using M9 with sodium acetate, which limited the growth of E. coli altogether as well as limiting the electrogenicity of other bacteria. It seems that electrogenicity can be linked to the growth of cultures, at least in the minimal media. This shows a great potential for using microbial half fuel cells in combination with different promoters and selectable markers. We are intending to further test this idea by using cells with arsenic promoter linked to the sucrose hydrolase gene. In such a system, detection of arsenic would induce expression of sucrose hydrolase, necessary for growth in media containing sucrose as the sole carbon source. In consequence such a system could be used as a reliable bio-detector generating data which would be easy to obtain and link to a computer system. With its potential for automation and miniaturisation this system offers a potential advancement in the field of biosensors.
We are also intending to proceed with testing our BioBricked napC and mtrA. After linking them to a promoter we would like to test their influence on potential generation. Overall, the system we have constructed gives repeatable results with E. coli and with further test we hope to create a system capable of providing reliable data which can be coupled to a variety of promoters and genes.
Acknowledgements
We would like to thank Dr Bruce Ward and Matthew Knighton for their help with the fuel cells and for lending us their lab equipment.
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