A Microbe-Powered Battery

When you think about batteries, you probably think of the standard electrochemical cells powered by chemical reactions. You might think of lead-acid batteries, car batteries, molten salt batteries, or even zinc-carbon batteries. You might think of battery-powered flashlights and electronic devices. But have you ever thought about microbes and batteries in the same thought bubble? Or more specifically - have you ever considered the idea of using bacteria to charge a battery? Probably not. But several scientists and groups worldwide have - and are currently prototyping ideas for how to make a ‘microbe-powered battery' a reality.

There's a strain of bacteria that's particularly special to the research behind this cause. Meet Shewanella oneidensis (left). This bacteria has the special property of being able to create nanowires that allow it to conduct electricity. Seems a bit unreal, right? These nanowires are made of protein that can connect circuits and thus create current. According to Mohamed El-Naggar, a biophysicist at USC, "This is the first measurement of electron transport along biological nanowires produced by bacteria." These nanowires hold enormous potential for further research, as scientists believe that the bacteria might be using them as a tool to communicate with each other. They could be a source of cohesion and communication in bacterial communities. According to El-Naggar, "This would be basically a community response to transfer electrons. It would be a form of cooperative breathing." Conducting electrons via nanowires would be a speedy, directed approach to signaling molecules and messages to individual members of a bacterial population. And in addition to the research scientists are conducting around the communication role of nanowires, there's also a more practical, commercial application they can be used in - creating potential batteries.

But how exactly does this bacterium generate electricity? And how can we use the electricity it generates in a battery-like structure? There are several factors that have to be put in place before the bacteria can actually use these nanowires to conduct current. The bacteria have to be in contact with a mineral surface, such as iron, manganese, or other minerals often found in deep sea sediment. According to Tom Clarke, a biologist at the University of East Anglia, U.K., "Our research shows that these proteins can directly 'touch' the mineral surface and produce an electric current, meaning that it is possible for the bacteria to lie on the surface of a metal or mineral and conduct electricity through their cell membranes." The bacteria needs this metal or mineral source in order to survive. According to Liang Shi, a microbiologist at Pacific Northwest National Laboratory in Richland, Wash., "Just as humans breathe oxygen and use it to generate energy, Shewanella bacteria can use minerals like iron oxide for respiration. The bacteria are known to produce a current by shuttling electrons across their cell membranes."

However, scientists aren't 100% sure about the exact mechanism and pathways the bacteria uses - this mystery is currently under ample investigation and research. Once we can figure out how exactly the bacteria functions and creates nanowires and electricity, the more knowledge we'll have in order to potentially use it as a bio-battery (or a battery using microbes) in the future. We could even possibly genetically engineer other microbes to do the same, and create clean, renewable energy devices that can supplant our existing fossil fuels.

References

Gorby, Y., et al. Electrically conductive bacterial nanowires produced by Shewanella oneidensis strain MR-1 and other microorganisms. PNAS. 103. 11358-11363. (2005).

Inman, M. Bacteria made to sprout conducting nanowires. NewScientist (2006).

Lewis, T. Electric Bacteria Could be Used for Bio-Battery. Livescience (2013).

Nanowire-armed Bacteria Become Living Biological Circuits. Livescience (2010).

Pirbadian, S., et al. Shewanella oneidensis MR-1 nanowires are outer membrane and periplasmic extensions of the extracellular electron transport components. PNAS. 111, 12883-12888. (2014).

Wire-like Structures Conduct Electricity: Shewanella oneidensis. BioMimicry Institute.

Picture Credits

Batteries (Brianiac, via Wikimedia Commons)

Shewanella oneidensis (via Wikimedia Commons)