Cyanobacteria Engineered to Accept External Electricity Turn Carbon Dioxide into Fuel
Source: Eleanor Clifford · CHEMISTRY WORLD · | September 27, 2021
Source: Chemistry World
Scientists have created a photo-electrosynthetic system that allows cyanobacteria to use both light and electricity to convert carbon dioxide into acetate or ethylene.1 The system is more energy efficient than natural photosynthesis and opens new avenues for coupling renewable electricity to photosynthetic microorganisms to sustainably produce fuels.
Photosynthesis, which converts carbon dioxide to useful carbon-containing compounds, is one of the most important bioprocesses on earth. However, natural photosynthesis suffers from three key limitations that reduce its overall efficiency. Firstly, photosystem I and photosystem II, which absorb light and excite electrons during photosynthesis, have overlapping absorption spectra and so compete for light energy. Secondly, oxygen produced by photosystem II competes with carbon dioxide for the active site of RuBisCO, the enzyme responsible for fixing carbon dioxide. This causes photorespiration, which competes with the desired carbon fixation pathway. Thirdly, photosynthesis can only use light energy from a small region of the solar spectrum, approximately 400–700nm.
To overcome these limitations, a team of scientists lead by Jeffrey Blackburn and Wei Xiong at the National Renewable Energy Laboratory in the US, designed a system that allows cyanobacteria to use an external supply of electrons and light to drive carbon dioxide fixation. They genetically removed photosystem II from cyanobacteria and attached the modified cells to a cathode within an electrochemical circuit. Under light illumination, the externally supplied electricity acted as an artificial photosystem II by delivering electrons to photoexcited photosystem I, allowing the cells to convert carbon dioxide into fuel molecules such as acetate and ethylene. By removing photosystem II ‘we block the photosystem, which is relevant to oxygen evolution, so the photorespiration process could be inhibited,’ explains Wei. ‘At the same time, there’s only one photosystem required in our system, so there’s no competition for light absorbance.’