Bacterial “skyscrapers” produce electricity

A new housing complex for bacteria could be used to power the future! Harry Lewis spoke to Jenny Zhang from the University of Cambridge to tell us more...

Harry - Jenny, I think we're gonna have to start off with the obvious question. What on earth is this bacteria and how can it produce energy?

Jenny - Yes, let me tell you about the lovely inhabitants of this new residence: cyanobacteria, they're the most abundant life form on earth. They're actually the ancestors to some components of plant cells that carry out photosynthesis. Essentially, they are different to other bacteria because they acquire their energy from sunlight and they use this energy to combine water and air in very creative ways to produce complex molecules like sugars and biomass.

Harry - Jenny, how do you manage to get that energy that's being produced? How do you manage to take that out and create electricity?

Jenny - One really fascinating phenomena of cyanobacteria is that they leak electrons to the outside of their cells during photosynthesis. Now, this is a big loss for them since it's really hard work to get those electrons in the first place, but it's a really big gain for us because when you place these bacteria on conductive surfaces - that is, electrodes - and then shine light on them, they essentially produce free electricity for us. To answer the question what are these type of housing units that we're designing, essentially, we are trying to design electrodes that can collect as many of these waste electrons as possible. These types of structure that we're building are extremely conductive pillars with microscopic structures that can hold a lot of these cyanobacteria. You can think of them as skyscrapers or high rise homes for cyanobacteria cells, so that they can be very effective during photosynthesis and for us to harvest their electrons,

Harry - This technology - converting sunlight into electricity - sounds a lot like our solar panels. Am I being naive, or is there a big difference between the two?

Jenny - They are very similar, but there is a big difference. The biggest difference is how the electrons are being used in the two different technologies. Solar panels absorb light energy and then use that energy to move electrons around in a closed circuit. So, by itself, solar panels can only generate electricity. But, in the type of technologies that we are trying to develop, they generate electricity because of the movement of electrons, but the electrons aren't in a closed circuit; they have to be first extracted from some molecule - water, for example, which is a very sustainable and abundant resource. Then, they have to be moved and inserted into the bonds of a new molecule. In that way, it helps us to form new fuels or chemicals that we want to perhaps produce in the future in a very sustainable way. Basically, what I'm saying is that our technology is different because of the way that it uses electrons to make new molecules.

Harry - This idea of taking bacteria and generating electricity, I'm assuming it's been around for a little while, but I've noticed that your research has found that you can really generate quite a bit more. Why was it that the theoretical and the practical accumulation of energy wasn't reaching its intended or theoretical potential beforehand?

Jenny - Scientists have been looking at this for a long time and they've been working very hard to, for example, bioengineer different pathways within the bacteria so that they can give up more of their electrons. These have yielded some improvements. However, this is a very multifaceted problem, and I'm really lucky because I'm working with a fantastic team of people with very different expertise; engineers, chemists, physicists, biologists, and we're all just chipping away at the same problem. We've discovered that the one big bottleneck that was stopping us from achieving the high theoretical values that were predicted for a long time was the electrode itself. The electrodes weren't allowing enough of the sunlight to be captured by the bacteria and they weren't capturing all the electrons. By smartly rethinking the design of the electrodes, we've been able to increase the output by 10-fold. This means that we can demonstrate, and have demonstrated, that those theoretically predicted values are within reach.

Harry - What could this lead to in terms of energy creation or energy generation? Could you see these structures actually popping up in places over the globe in the future?

Jenny - Absolutely. We're dreaming big, right? We know that cyanobacteria is highly scalable. They can grow pretty much anywhere where there's water, air and sunlight, and that's why they're the most abundant life on earth. You can grow them in your pond, they can be found in glaciers, in deserts, and also in the ocean, which covers 70% of Earth's surface. I imagine that we can use these in a variety of places, but this type of technology would be great for producing electricity as well as chemicals. That's what distinguishes them from solar panels. They can also be used to make chemicals and fuels and, in doing so, in a decentralized manner, which will hopefully be affordable and sustainable at the same time because these materials are highly biodegradable and very renewable.

Harry - And putting them in remote areas would be fantastic. What a great use of space. Jenny Zang there, and her research was published in the journal Nature Materials earlier in the week, 'Bioenergy. Is it a necessary tool in our race to reach zero carbon energy?' I'll let you decide.