Scientists at the University of East Anglia have made an important breakthrough in the quest to generate clean electricity from bacteria.
Findings published today in the journal Proceedings of the National Academy of Sciences (PNAS) show that proteins on the surface of bacteria can produce an electric current by simply touching a mineral surface.
The research shows that it is possible for bacteria to lie directly on the surface of a metal or mineral and transfer electrical charge through their cell membranes. This means that it is possible to 'tether' bacteria directly to electrodes - bringing scientists a step closer to creating efficient microbial fuel cells or 'bio-batteries'.
The team collaborated with researchers at Pacific Northwest National Laboratory in Washington State in the US. The project was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the US Department of Energy.
Shewanella oneidensis is part of a family of marine bacteria. The research team created a synthetic version of this bacteria using just the proteins thought to shuttle the electrons from the inside of the microbe to the rock.
They inserted these proteins into the lipid layers of vesicles, which are small capsules of lipid membranes such as the ones that make up a bacterial membrane. Then they tested how well electrons travelled between an electron donor on the inside and an iron-bearing mineral on the outside.
Lead researcher Dr Tom Clarke from UEA's school of Biological Sciences said: "We knew that bacteria can transfer electricity into metals and minerals, and that the interaction depends on special proteins on the surface of the bacteria. But it was not been clear whether these proteins do this directly or indirectly though an unknown mediator in the environment.
"Our research shows that these proteins can directly 'touch' the mineral surface and produce an electric current, meaning that is possible for the bacteria to lie on the surface of a metal or mineral and conduct electricity through their cell membranes.
"This is the first time that we have been able to actually look at how the components of a bacterial cell membrane are able to interact with different substances, and understand how differences in metal and mineral interactions can occur on the surface of a cell.
"These bacteria show great potential as microbial fuel cells, where electricity can be generated from the breakdown of domestic or agricultural waste products.
"Another possibility is to use these bacteria as miniature factories on the surface of an electrode, where chemicals reactions take place inside the cell using electrical power supplied by the electrode through these proteins."
Biochemist Liang Shi of Pacific Northwest National Laboratory said: "We developed a unique system so we could mimic electron transfer like it happens in cells. The electron transfer rate we measured was unbelievably fast - it was fast enough to support bacterial respiration."
The finding is also important for understanding how carbon works its way through the atmosphere, land and oceans.
"When organic matter is involved in reducing iron, it releases carbon dioxide and water. And when iron is used as an energy source, bacteria incorporate carbon dioxide into food. If we understand electron transfer, we can learn how bacteria controls the carbon cycle," said Shi.
Notes to editors
'Rapid electron exchange between surface-exposed bacterial cytochromes and Fe(III) minerals' by Thomas A Clarke, Gaye White, Julea N Butt, and David J Richardson (all UEA. UK), and Zhri Shi, Liang Shi, Zheming Wang, Alice C Dohnalkova, Matthew J Marshall, James K Fredrickson and John M Zachara (all PNNL, USA) is published by PNAS on Monday, March 25.
For more information, images, or to arrange an interview with Dr Tom Clarke at UEA, please contact Lisa Horton in the UEA Press Office on +44 (0)1603 592764. To arrange an interview with researchers at PNNL, contact Mary Beckman in their press office by emailing firstname.lastname@example.org or call (USA) +1 509-375-3688.
About the UEA
The University of East Anglia (UEA) was founded in 1963 and this year celebrates its 50th anniversary. It has played a significant role in advancing human understanding and in 2012 the Times Higher Education ranked UEA as one of the 10 best universities in the world under 50 years of age. The university has graduated more than 100,000 students, attracted to Norwich Research Park some of Britain's key research institutes and a major University Hospital, and made a powerful cultural, social and economic impact on the region. www.uea.ac.uk/50years
UEA's School of Biological Sciences is ranked 14th in the Guardian League Table 2013 and 90% of research activity was classified as internationally leading, excellent or recognised in the latest Research Assessment Exercise. The school was ranked first for teaching in the 2012 National Student Survey. www.uea.ac.uk/bio
Interdisciplinary teams at Pacific Northwest National Laboratory (PNNL) address many of America's most pressing issues in energy, the environment and national security through advances in basic and applied science. PNNL employs 4,500 staff, has an annual budget of nearly $1Bn, and has been managed for the U.S. Department of Energy by Ohio-based Battelle since the laboratory's inception in 1965.
BBSRC invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.
Funded by Government, and with an annual budget of around £500M (2012-2013), we support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.