Contents

Geobacter Lab

The Project

Introduction
In the year 1987, a year in which a great amount of this year's VSF participants were born, a species of bacteria was isolated from the Potomac River downstream of Washington DC. This species, later named Geobacter metallireducens, caused a great stir because it "breaths" iron the same way we breath oxygen. In other words, in cellular respiration, iron oxides are the final electron acceptors. Since then, Dr. Derek Lovley and his fellow researchers have isolated many different strains, and the applications for them include alternative energy sources and bioremediation.

What kind of research is the lab involved in?
This laboratory is devoted almost exclusively to the study of the Geobactercaea family of microorganisms. The research that is included on this part of the site is focused on the research conducted by the Geobacter Project under the Department of Microbiology of the University of Massachussetts. The stuff they do includes classifying new microorganisms, decoding the genetic factors behind the miraculous things these bacteria do, testing to discover all the different chemicals they can reduce, and finding ways to improve their efficiency in performing vital jobs like bioremediation and energy production. They study the bacteria both in situ (in their natural environment) and in chemostats, a contraption used to grow bacteria by constantly replacing the culture medium.

Transmission electron micrograph of Rhodoferax ferrireducens.

Research in the lab is not limited to the exploration of Geobacter, as the name of the project might suggest. In fact, one of the microorganisms the lab is currently looking at, Rhodiferax ferrireducens, is also capable of directly tranferring electrons onto an electrode.

What kind of bacteria do they use?
One of the things the Geobacter project tries to do is find bacteria that can effectively and efficiently produce energy. Bacteria undergo a form of cellular respiration that is similar in some respects to human cellular respiration. Just by looking at the species' name in many of the Geobacter bacteria, you can tell what the last electron acceptor is. Though it was thought that Geobacter were anaerobic, it turns out that Geobacter sulfurreducens can in fact use oxygen as an electron acceptor as well, which increases the chances for it to be adapted into out-of-habitat applications.

The specialness of the Geobacters lie in their ability to produce energy without a mediator. MFCs used to rely on toxic mediators to shuttle electrons to the electrodes of the fuel cell. Geobacter circumvent this problem by attaching directly onto the surface of the electrode. Except for laboratory growth, the public does not need to get into the details of the typical Geobacter diet because Geobacter are primarily used in situ in the seafloor microbial fuell cell described on another page of this site.

A species closely related to the Geobacters is Rhodoferax ferrireducens, a more portable bacteria because it can oxidize carbohydrates like sugar, a substance that is not only found in abundance, but is renewable. This particular brand of microorganism was isolated in an aquifer sediment in Virginia. These bacteria also have the special ability to walk around the mediator problem by attaching directly onto the electrode. They also boast an 80% efficiency, as if their numerous other qualifications were not enough. Previous fuel cells such as the yeast-powered MFC that's being developed by Dr. Linwei Lin could only operate at aound 1%.

In the fuel cell for R. ferrireducens, the electrons that are let loose in by the bacteria from the sugar into the anode want to go to the oxygen in the cathode, but since they can't go directly, they have to go through the wire. In this way, the elecrons, by way of reaching their destination, provide us with current. The only problem with this MFC is that the process is extremely slow for what the scientists hope to accomplish with it, though in theory it could make a cup of sugar power a 60 watt bulb for 17 hours.

Geobatteries powering a calculator.

The Future

The MFC with R. ferrireducens is still in the experimental stages. Scientists are now focused on testing various materials and chemicals to improve efficiency and testing to discover properties of the bacteria. Right now there are no specific applications in mind.

Dr. Derek Lovley, the Head Researcher for the Geobacter project, says, "I don't want to give the impression that it's 'Back to the Future,' where we stuff a banana in the engine and go, but it's a pretty good leap from where microbial cells where before."