This presentation goes over the basic concept of a Microbial Fuel Cell (MFC), the challenges of MFC efficiency, and the genetic approach to engineering bacteria to address these challenges.

1. Genetic Engineering of Bacteria for an MFC
Marshall Porter - Biomolecular Eng
Sai Edara - Biomolecular Eng
Aaron Maloney - Bioelectronics Eng
David Dillon - Biomolecular Eng
Christian Pettet - Biomolecular Eng
Arjun Sandhu - Biomolecular Eng
Ansley Tanoto-MCD Bio/Bioinformatics
Alex Ng- Biomolecular Eng

2. Addressing Energy Demand
According to the 2013 International Energy Outlook, energy
demands will increase 56% by 2040. This rapidly growing
demand for energy has sparked a search for sustainable,
renewable, and cheap energy sources. One intriguing new
energy technology is the Microbial Fuel Cell (MFC), capable of
turning wastewater treatment into an electricity generating
process.

3. The bacteria Shewanella oneidensis
● Can live in both environments
with or without oxygen
● Can reduce poisonous heavy
metal
● Has “electrogenic” properties
allowing it to generate
electricity in a Microbial Fuel
Cell (MFC).
http://www.newscientist.com/article/dn9526-
bacteria-made-to-sprout-conducting-
nanowires.html#.U9gp_LEzCM0

4. What is an MFC?
● Microbes Break down
Carbohydrates
● Transfer electrons to anode,
which then flow to the cathode
● Protons pass through
permeable membrane
● Protons and electrons react
with oxygen to make clean
water
● Can be implemented into
secondary treatment of waste-
water to allow for power
generation[5]
http://www.sciencebuddies.
org/Files/3665/5/Energy_img033.jpg

5. Physical
Design
● A lot of previous research has
looked at structural design
● Two main points
○ Large surface area on
electrode
○ Close distance between
electrodes
http://2013.igem.org/Team:Bielefeld-
Germany/Project/MFC

6. Our Project
● We believe the bacteria which drive the power generation of an
MFC can be genetically engineered to increase power density
● Our goal is to design MFC with increased efficiency by
○ Altering metabolism of our electrogenic bacteria
○ Modifying growth pattern of biofilm formation
● Two pronged approach, each with potential to improve efficiency
alone

7. Energy Balance and Coulombic Efficiency
● The process of metabolism and electron transfer is
complex.
● The cell itself uses up some of the energy in other
processes
● One such process is metabolite generation, which
reduces coulombic efficiency.[1]
● We plan to redirect metabolism toward a pathway
capable of harvesting the lost energy

8. ● When Shewanella is grown
without oxygen, it generates the
metabolite acetate from acetyl-
coa
Acetate generation
[3]

9. ● “gate keeper” to the TCA cycle
● Converts acetyl-CoA and
Oxaloacetate to Citrate
● Diverts Acetyl-CoA from being
converted to Acetate
(metabolite)
Citrate Synthase (GltA)

10. ● Under anaerobic conditions
Shewanella is capable of
using the oxidative branch of
TCA, which allows the
bacteria to use the energy
lost by metabolite generation
● Use of oxidative branch is
reliant on Citrate Synthase
activity
Oxidative
branch
Oxidative branch of TCA

11. Citrate Synthase
● Under the anaerobic conditions citrate synthase activity
reduced by over one half due to downregulation of the gltA
gene coding for citrate synthase [3]
● In our project we will recover this activity using an
expression plasmid
(gene deletion)
[3]

12. ● Magnitude of electron transfer reliant on
surface area of the anode
○ More surface area allows more bacteria
to transfer electrons
○ Growth of bacteria in biofilm allows for a
dense community to grow in one area
● Growth of Shewanella in anaerobic
conditions leads of down regulation of biofilm
production, and biofilm density is lost
Biofilm

13. Biofilm
● Biofilm formation in Shewanella is
controlled by the gene mxdA, which
regulates levels of c-di-GMP
● Upon deletion of mxdA, biofilm
biomass decreases (fig A, mxdA)
● Biomass also decreases when
switching from oxic to anoxic
growth (fig B, control) but is
retained when a gene similar to
mxdA is expressed (fig B,
VCA0956)[7]
● We hope to express VCA0956 in
Shewanella while it grows in the
MFC anaerobically to increase
biofilm density
A
B
[7]

14. Waste-water treatment
● Treatment of waste water can be divided into three main steps
1. Heavy and light materials are removed by separation in a holding tank
2. Microorganisms are used to break down organic matter
3. Water is disinfected to be reintroduced to environment
http://en.wikipedia.

15. Implementation
● A microbial fuel cell can be implemented into
secondary waste water treatment processes, and
potentially in septic tanks as well
● There are other applications of electrogenic bacteria
as well, including microbial electrolysis cells used to
generate hydrogen fuel

16. Citations
1. Korneel Rabaey, ed. Bioelectrochemical systems: from extracellular electron transfer to biotechnological
application. IWA publishing, 2010.
2. Franks, Ashley E., and Kelly P. Nevin. "Microbial fuel cells, a current review." Energies 3.5 (2010): 899-919.
3. Brutinel ED, Gralnick JA. Anomalies of the anaerobic tricarboxylic acid cycle in Shewanella oneidensis
revealed by Tn-seq. Mol Microbiol. 2012 Oct;86(2):273-83. doi: 10.1111/j.1365-2958.2012.08196.x. Epub
2012 Aug 27. PubMed PMID: 22925268.
4. Papagianni M. Recent advances in engineering the central carbon metabolism of industrially important
bacteria. Microb Cell Fact. 2012 Apr 30;11:50. doi: 10.1186/1475-2859-11-50. Review. PubMed PMID:
22545791; PubMed Central PMCID: PMC3461431
5. Rabaey K, Verstraete W. Microbial fuel cells: novel biotechnology for energy generation. Trends Biotechnol.
2005 Jun;23(6):291-8. Review. PubMed PMID: 15922081.
6. Beliaev, Alex S., et al. "Gene and protein expression profiles of Shewanella oneidensis during anaerobic
growth with different electron acceptors." Omics: a journal of integrative biology 6.1 (2002): 39-60.
7. Thormann, Kai M., et al. "Control of formation and cellular detachment from Shewanella oneidensis MR-1
biofilms by cyclic di-GMP." Journal of Bacteriology 188.7 (2006): 2681-2691.