Toby Call: Rhodo graphene anode, 2nd Prize in the ZEISS Photography Competition 2016
Taken on an FEI Verios 460 scanning electron microscope in the Advanced Imaging Centre in Cambridge, freezing the samples preserved biological structures of the cells without desiccation. In the image the purple non-sulpur bacterium Rhodopseudomonas palustris CGA009 (red) can be seen colonizing the surface of the electrically conductive graphene coated carbon foam. Nanowires can be seen protruding from some cells and attaching either directly to the graphene surface, providing a direct bio-electrical interface, or to other cells in a circuit that extends the reach of each cell. Dominating the image is a rampaging contaminant, most likely a eukaryotic unicellular ciliate, bursting from the darkness in a frenzy of tentacle like cilia.
The first reports of electricity being generated directly from bacteria appeared over 100 years ago. Today, with improvements in imaging techniques and genetic engineering methods we are starting to fully understand why microorganisms expel electrons, how some bacteria have evolved particularly efficient ways of connecting electrically to their surroundings, and what these enabling outer membrane cytochromes and type IV conductive pili are made of.
Electrons are the currency of life, we strip them from our food to power the engine of chemiosmosis and generate proton gradients across membranes in our mitochondria that in turn drive ATP synthesis. Once they have passed through the finely tuned chemiosmotic machinery, we pass them onto oxygen in a hurry. Hold your breath and you’ll see how finely balanced that energy churning process is. In environments devoid of oxygen, many microorganisms have evolved different ways of donating electrons to a terminal electron acceptor, including directly passing them to a conductive material outside the cell and across the protective layers of the outer membrane.
We can build simple devices designed to harness electrons produced by such ‘exoelectrogenic’ bacteria. Maximum power outputs from lab scale devices reach into the hundreds of Watts per metre cubed, impressive by biological standards given these are living cells, but perhaps leaving something to be desired if competing with conventional renewable energy sources. Where microbial fuel cells (MFCs) are at an advantage is in harnessing biochemical ability of the microorganisms to use waste substrates as their food, ejecting spent electrons for our benefit. Early stage examples of MFC technology in the real world harness waste streams from breweries or farms in order to give power back to the plant. Potential applications include miniaturised devices acting as sensitive biosensors or as a means for power generation in remote areas including deep space exploration.
We are working to improve the rate of electron transfer by optimizing the electrode material. Graphene is a promising material due to its high conductivity, biocompatibility, relatively low cost, and importantly its ease of incorporation into extremely high surface area materials that maximize cell to electrode contact. The image here could represent one of the major challenges to scaling up bioenergy production, namely the instability of monocultures and vulnerability to contamination that so often scuppers industrial efforts to bring bioenergy solutions into the commercial world.
Contributors:
Toby Call, Final year PhD student in Prof. Chris Howe’s lab, Department of Biochemistry: Performed the experiment and imaged the material after Tian Carey and Dr. Felice Torrisi, PhD and PI respectively in the Graphene Centre, Department of Electrical Engineering: coated carbon foam anode with pure graphene Dr. Paolo Bombelli, Post-doc., Department of Biochemistry: design and construction of microbial fuel cells Dr. Jeremy Skepper, Advanced Imaging Centre, Anatomy Department: sample preparation and loading
Toby Call: Rhodo graphene anode, 2nd Prize in the ZEISS Photography Competition 2016
Taken on an FEI Verios 460 scanning electron microscope in the Advanced Imaging Centre in Cambridge, freezing the samples preserved biological structures of the cells without desiccation. In the image the purple non-sulpur bacterium Rhodopseudomonas palustris CGA009 (red) can be seen colonizing the surface of the electrically conductive graphene coated carbon foam. Nanowires can be seen protruding from some cells and attaching either directly to the graphene surface, providing a direct bio-electrical interface, or to other cells in a circuit that extends the reach of each cell. Dominating the image is a rampaging contaminant, most likely a eukaryotic unicellular ciliate, bursting from the darkness in a frenzy of tentacle like cilia.
The first reports of electricity being generated directly from bacteria appeared over 100 years ago. Today, with improvements in imaging techniques and genetic engineering methods we are starting to fully understand why microorganisms expel electrons, how some bacteria have evolved particularly efficient ways of connecting electrically to their surroundings, and what these enabling outer membrane cytochromes and type IV conductive pili are made of.
Electrons are the currency of life, we strip them from our food to power the engine of chemiosmosis and generate proton gradients across membranes in our mitochondria that in turn drive ATP synthesis. Once they have passed through the finely tuned chemiosmotic machinery, we pass them onto oxygen in a hurry. Hold your breath and you’ll see how finely balanced that energy churning process is. In environments devoid of oxygen, many microorganisms have evolved different ways of donating electrons to a terminal electron acceptor, including directly passing them to a conductive material outside the cell and across the protective layers of the outer membrane.
We can build simple devices designed to harness electrons produced by such ‘exoelectrogenic’ bacteria. Maximum power outputs from lab scale devices reach into the hundreds of Watts per metre cubed, impressive by biological standards given these are living cells, but perhaps leaving something to be desired if competing with conventional renewable energy sources. Where microbial fuel cells (MFCs) are at an advantage is in harnessing biochemical ability of the microorganisms to use waste substrates as their food, ejecting spent electrons for our benefit. Early stage examples of MFC technology in the real world harness waste streams from breweries or farms in order to give power back to the plant. Potential applications include miniaturised devices acting as sensitive biosensors or as a means for power generation in remote areas including deep space exploration.
We are working to improve the rate of electron transfer by optimizing the electrode material. Graphene is a promising material due to its high conductivity, biocompatibility, relatively low cost, and importantly its ease of incorporation into extremely high surface area materials that maximize cell to electrode contact. The image here could represent one of the major challenges to scaling up bioenergy production, namely the instability of monocultures and vulnerability to contamination that so often scuppers industrial efforts to bring bioenergy solutions into the commercial world.
Contributors:
Toby Call, Final year PhD student in Prof. Chris Howe’s lab, Department of Biochemistry: Performed the experiment and imaged the material after Tian Carey and Dr. Felice Torrisi, PhD and PI respectively in the Graphene Centre, Department of Electrical Engineering: coated carbon foam anode with pure graphene Dr. Paolo Bombelli, Post-doc., Department of Biochemistry: design and construction of microbial fuel cells Dr. Jeremy Skepper, Advanced Imaging Centre, Anatomy Department: sample preparation and loading