Thank you for your interest and for your questions, JKMakowka and isis, and our apologies for this long overdue reply.

With respect to JKMakowka's questions:

We have only so far tested these microbial fuel cells (MFCs) in batch mode. However, unlike conventional, exogenously added redox mediators/shuttles, our synthetic wires appear to be strongly localized to the microbial membranes and do not appear to leach out of the membranes of healthy cells with time. In addition, we use them at much lower concentrations (e.g., tens of micromolar, versus millimolar scale for conventional redox mediators). So, although they may likely be 'diluted down' from the perspective of 'number of wires per cell' as the microbes grow and divide, we don't anticipate a great need for 'replenishment' in an operating system, which may lead to relatively reduced costs.

At this point, the impact these molecules have on eukaryotic cells (and on the environment) is uncertain. The concentration at which such molecules are applied would likely have a significant effect. However, for comparison, the work of Prof. David G. Whitten on similar molecular systems has shown little toxicity to mammalian cells, which is encouraging from our perspective. More work will certainly have to be carried out to better answer such questions.

With respect to isis' questions:

There isn't necessarily an energy cost to run this system, per se. In principle, the microorganisms are using organic contaminants in the wastewater as a fuel source, from which a certain amount of the electrons captured metabolically are harvested to generate electricity. The fuel cells do, however, work better at temperatures above ambient temperature, so there could be associated costs of maintaing such devices at moderately elevated temperatures (e.g. 30-40 degrees C).

Our devices have not been optimized for efficiency, as we were more focused on demonstrating the ability of synthetic wires to show an improvement in performance, in general. At this point, our devices are rather low energy-yielding, but with improvements to the engineering of the devices, better absolute electrochemical performance may be achieved.

Our synthetic wires are not yet available for commercial sale.

There are certainly challenges that remain to be overcome by MFCs, in general, prior to becoming an industrially viable technology. Our focus was not necessarily to engineer a better device, but to demonstrate that addition of a synthetic modifier (that behaves rather differently than conventional redox mediators) to microorganisms may help facilitate the transfer of electrons across the typically insulating membrane--electrode interface. This interface has been identified as a major barrier to achieving efficient coupling of cells to electrodes in bioelectronic/bioelectrochemical devices. This may allow for the possibility of electrochemically interfacing a larger variety of microbial species to electrodes for use in potentially transformative technologies.

How much energy will you need to run this system vs how much energy will it produce?
So, if I understand it right, this system doesn't require addition of chemicals, but synthetic wires must be added? Is there a supplier of these synthetic wires in Nairobi or Dakar?
I suppose the challenge is to get this off the lab bench and into the real world. MFCs so far have not succeeded to go past the short-term pilot tests. Although the vast majority are just lab experiments. Why is this and how is this project different?

Dear all,

I am pleased to introduce our research project here on the SuSanA Forum.

Title of grant: Design of Microorganisms with Semiconducting Membranes

Lead organization: University of California Santa Barbara
Contact: Guillermo Bazan

Partners : Dr. James J. Sumner (U.S. Army Research Laboratory); Dr. Steven P. Harvey (U.S. Army Edgewood Chemical Biological Center); Dr. Christian J. Sund(U.S. Army Research Laboratory); Prof. Derek R. Lovley (UMass Amherst); Prof. Arum Han(Texas A&M University); Prof. Joachim S. C. Loo (Nanyang Technological University,Singapore); Dr. Jamie Hinks (Nanyang Technological University, Singapore)

Location of research: USA and Singapore

Start and end date: May 1, 2011 – May 1, 2013
Grant type: Grand Challenges Explorations (GCE), Round 6

Goal: The goal of this project is to introduce artificial molecular wires into the membranes of microbes within a waste treatment system as a way to break down organic contaminants in human waste and catalytically convert the metabolic energy in those microbes into electrical energy.

Short description of the project: Our idea is to use naturally occurring microorganisms in order to turn sanitary waste into electricity. The main innovation is the use of synthetic conducting molecular wires that self assemble within microbial membranes, thereby increasing electrical conductivity and enabling extraction of electricity from contaminants in sanitary wastewater. Creating a technology that utilizes these modified microorganisms in conjunction with bioelectrochemical devices offers an innovative solution for the design of decentralized sanitary wastewater treatment. Instead of using industrial additives, like chlorine or other disinfectants, our approach relies on the biodegradation of harmful contaminants by taking advantage of the metabolic activity in native microbial communities. Moreover, electricity or biofuel production may be harnessed from this process and be recycled back into the sanitary waste treatment process or be used directly on-site to serve the needs of the local community. Biggest successes so far and current state of affairs: We have demonstrated that microorganisms modified with transmembrane wires can enhance electricity production in microbial fuel cells by more than 400%. Microbial fuel cells incorporating modified Escherichia coli (a common species, which is part of the normal flora of the gut and is an indicator species for fecal bacteria) have been successfully employed. In addition, microbial fuel cells incorporating real wastewater as a source of both microorganisms and carbon source have also shown significant enhancement of electricity production with a concomitant decrease in the content of organic contaminants as a result of incorporating our synthetic wires. The results obtained with real wastewater are noteworthy as they show that the molecular wires may be added to ill-defined wastewater to elicit electrochemical activity from a native microbial population.

Using a metagenomic approach, we have recently obtained data that suggests that addition of synthetic wires to a mixed microbial community causes significant shifts in the makeup of the population. Some of the specific species within a mixed wastewater community wastewater that are most greatly affected by addition of our synthetic wires have also been identified. This information will be valuable as we strive for a more targeted approach to modifying microorganisms to further improve their efficiency when employed in bioelectrochemical devices to address the management of sanitary waste.



Main challenges : Metagenomic data provides a broad picture of the microbial wastewater community and analysis of such data can reveal changes in the microbial population as a result of adding our synthetic wires. However, the complexity of these microbial communities and their interspecies interactions renders it difficult to isolate the various effects exerted on the population as a result of modification with our synthetic wires. Although this has not specifically hampered our ability to provide proof-of-concept examples, the use of model wastewater populations is being considered for future studies in order to establish a better understanding the role of molecular wires in promoting electrical power generation to further improve device performance.

A second issue pertains to improving the Coulombic efficiencies of the systems described above. As electrical power generation is partly proportional to the contact area between the microbial biofilm and the charge-collecting electrode, we are considering routes for optimizing biofilm coverage of the electrodes. This includes, for example, pre-modification of the electrode surface with our molecular wires to facilitate more widespread and uniform cell attachment

Links and further readings:
Bazan Group Homepage: www.chem.ucsb.edu/bazangroup/

Relevant Literature:
• Garner, L. E.; Thomas, A. W.; Sumner, J. J.; Harvey, S. P.; Bazan, G. C. Conjugated Oligoelectrolytes Increase Current Response and Organic Contaminant Removal in Wastewater Microbial Fuel Cells. Energy Environ Sci. 2012, 5, 9449;
• Hou, H.; Chen, X.; Thomas, A. W.; Catania, C.; Kirchhofer, N. D.; Garner, L. E.; Han, A.; Bazan, G. C. Conjugated Oligoelectrolytes Increase Power Generation in E. coli Microbial Fuel Cells. Adv. Mater. 2013, 25, 1593;
• Wang, V. B.; Du, J.; Chen, X.; Thomas, A.; Kirchhofer, N.; Garner, L.; et al. Improving Charge Collection in Escherichia coli–Carbon Electrode Devices with Conjugated Oligoelectrolytes. Phys. Chem. Chem. Phys. 2013, 15, 5867.

Kind regards,
Jenny Du

University of California
Santa Barbara

Interesting idea!
How did you run the microbial fuel cells, or to ask differently: if not in batch-mode, how much of your "wires" had to be replaced constantly to off-set bacteria being washed out? And what would be the cost implications of this?

Also, could those wires by themselves form an environmental or health hazard? Could they for example disrupt mitochondria energy production in small eucaryotes abundant in natural surface waters?