Microbial carbon cycling under geological CO2 storage conditions: understanding the rules of life in the engineered subsurface

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In recognition of the growing global climate emergency caused by the increase in carbon dioxide (CO2) emissions from fossil fuel use, the UK government recently passed into law a commitment to reach net zero emissions by 2050. This ambitious target not only calls for a transition from fossil fuels to renewable energy, but also for the direct removal of CO2 emissions from the atmosphere. A compelling way to do this is with carbon capture and storage, whereby CO2 from fossil fuel use is captured at source (for example power plants and cement factories) and transported for safe storage 0.8 km or more beneath the surface of the Earth. In order for this carbon capture and storage approach to succeed, captured CO2 must be injected into deep geological formations, such as high salinity sandstone aquifers, on a permanent basis. These formations have the right geological characteristics for CO2 storage, and numerous pilot projects have demonstrated that the injection of large volumes of CO2 into these subsurface environments is possible. However, recent research has shown that these subsurface environments are inhabited by diverse and active communities of microorganisms, and the impacts of microbial activity in a deep geological CO2 storage environment are not known.Microorganisms are capable of using CO2 for their metabolism, and the injection of CO2 into deep subsurface environments is likely to cause a shift in the composition and function of microbial communities towards those capable of exploiting CO2 for growth. This could result in positive impacts, such as enhanced sequestration of CO2 and conversion into biomass (akin to locking away CO2 by planting trees), or negative impacts, such as the production of extra gases that may trigger leakages from the storage reservoir. The research I propose to conduct is designed to better understand the role of microorganisms in a geological CO2 storage facility, and to identify ways in which microorganisms might be harnessed to lock away more CO2 in these environments and even convert waste CO2 into useful chemicals, such as biofuels. I will mimic the conditions of a deep geological CO2 storage reservoir using bespoke 'bioreactors' that allow microbial communities to be studied under the elevated temperatures and pressures common to the subsurface. Throughout these experiments, and in follow-on targeted experiments, I will apply state-of-the-art geochemical and 'omics' techniques to monitor changes to the chemistry and microbiology of the system. A particular focus of this work is to understand how individual organisms in a microbial community work together in driving metabolic processes. These interactions occur in all microbial communities, but are not well understood. Using cutting-edge tools, I will identify and characterise these interactions and in doing so unearth the role of these microbial processes on CO2 storage in unprecedented detail. These results will be used to develop computer models of these communities, enabling predictions to be made on the role of these microbial communities under different conditions. Using these predictions, we can learn how to harness the power of microorganisms in the subsurface to help the UK reach its zero emissions target by 2050.