Renewable bioenergy generation aided by ‘skyscraper’ bacteria

A research team from the University of Cambridge has developed ‘skyscrapers’ for communities of bacteria to aid in renewable bioenergy generation.

How did scientists develop these bacteria?

The researchers utilised 3D printing to create grids of high-rise ‘nano-housing’ where sun-loving bacteria can grow at a quick rate. This meant that scientists were then able to extract the bacteria’s waste electrons, left over from photosynthesis, which could be utilised in renewable bioenergy generation, to power small electronics.

Past experiments have taken the approach of extracting energy from photosynthetic bacteria. However, the Cambridge researchers have found that providing them with the right kind of environment increases the amount of energy they can extract by over an order of magnitude.

Thus, this approach is competitive against traditional methods of generating renewable bioenergy and has already reached solar conversion efficiencies that can outcompete numerous existing methods of biofuel generation.

What did the experiment reveal regarding renewable bioenergy generation?

Their results, reported in the journal Nature Materials, open new avenues in bioenergy generation and suggest that ‘biohybrid’ sources of solar energy could be an important component in the zero-carbon energy mix.

Current renewable technologies, such as silicon-based solar cells and biofuels, are far superior to fossil fuels in terms of carbon emissions, but they also have limitations, such as a reliance on mining, challenges in recycling, and a reliance on farming and land use, which results in biodiversity loss.

“Our approach is a step towards making even more sustainable renewable energy devices for the future,” explained Dr Jenny Zhang, leader of the study from the Yusuf Hamied Department of Chemistry.

Zhang and her colleagues from the Department of Biochemistry and the Department of Materials Science and Metallurgy are working to rethink bioenergy into something that is sustainable and scalable.

What issues have scientists faced in developing these bacteria?

Photosynthetic bacteria, or cyanobacteria, are the most abundant life form on Earth. For several years, researchers have been attempting to ‘re-wire’ the photosynthesis mechanisms of cyanobacteria in order to extract energy from them.

“There has been a bottleneck in terms of how much energy you can actually extract from photosynthetic systems, but no one understood where the bottleneck was,” said Zhang. “Most scientists assumed that the bottleneck was on the biological side, in the bacteria, but we have found that a substantial bottleneck is actually on the material side.”

In order to grow, cyanobacteria need an abundance of sunlight, and in order to extract the energy they produce through photosynthesis, the bacteria need to be attached to electrodes.

How did researchers overcome these challenges?

The Cambridge team 3D-printed custom electrodes out of metal oxide nanoparticles that are tailored to work with the cyanobacteria as they perform photosynthesis. The electrodes were printed as highly branched, densely packed pillar structures, similar to ‘skyscrapers.’

Zhang’s team developed a printing technique that allows control over multiple length scales, making the structures highly customisable, which could benefit a wide range of fields.

“The electrodes have excellent light-handling properties, like a high-rise apartment with lots of windows,” explained Zhang. “Cyanobacteria need something they can attach to and form a community with their neighbours. Our electrodes allow for a balance between lots of surface area and lots of light – like a glass skyscraper.”

Once the self-assembling cyanobacteria were in their new home, the researchers found that they were more efficient than current bioenergy technologies, such as biofuels. The technique increased the amount of energy extracted, by over an order of magnitude above other methods typically utilised for producing bioenergy from photosynthesis.

Zhang concluded: “I was surprised we were able to achieve the numbers we did – similar numbers have been predicted for many years, but this is the first time that these numbers have been shown experimentally.

“Cyanobacteria are versatile chemical factories. Our approach allows us to tap into their energy conversion pathway at an early point, which helps us understand how they carry out energy conversion so we can use their natural pathways for renewable fuel or chemical generation.”

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