Accelerating carbon biomineralisation in seawater to help reduce atmospheric carbon dioxide

Project duration: June 2023–June 2026

Project lead

Team

Co-funded by the Advanced Engineering Biology and CarbonLock Future Science Platforms, the project team involves: Veena Nagaraj, Mihaela Grigore, Colin Scott, Oliver Mead, Andrew Warden, Robert Speight and Santou Sanyal.

Opportunity

Coral reefs have been major sinks of atmospheric carbon dioxide (CO₂) for around 500 million years. Animals such as corals and molluscs use templating proteins to aid the biomineralisation of  dissolved CO₂ in seawater and create up to 4 kg per m² per year of calcium carbonate (CaCO₃) in the form of exoskeletons and shells.

Engineering biology enables us to mimic these processes to occur outside a living organism, or to engineer fast-growing microorganisms, such as those that form organo-sedimentary structures like microbialites or stromatolites, that can be cultivated for accelerated carbon locking from the atmosphere via biomineralisation. In this process, we can identify and characterise different templating proteins that occur in nature and optimise their combinations to accelerate CaCO₃ formation using atmospheric CO₂. The resulting CaCO₃ could also be used in applications such as building materials, helping to offset carbon-intensive processes like concrete formation, which accounts for ~8% of global CO₂ emissions.

Enhancing and adapting naturally-occurring biogeochemical processes for carbon sequestration in controlled environments has not yet been widely explored, despite being a feasible method of deploying and scaling biomineralisation technology. What’s lacking is a deeper understanding of the biological processes and molecules involved and how they interact and influence the formation of geological structures. Unlocking this knowledge will bring us a step closer to efficient carbon storage and the significant market opportunities that exist for novel Intellectual Property (IP), green construction materials and carbon-offset credits.

Goal

The research will contribute to the fundamental biochemical understanding of how marine organisms capture and store carbon.

Carbon biomineralisation requires hydrogen carbonate ions (HCO₃^–) produced from CO₂, calcium ions, an alkaline pH, and templating proteins that nucleate unstructured CaCO₃ to crystalline forms aided by other biomolecules like collagens, fats, and sugars.

While there’s been considerable work done on characterising and optimising the enzymes carbonic anhydrase and urease that make HCO₃^– from CO₂ for biological carbon capture, there’s been surprisingly little work done on identifying how templating proteins initiate and influence the CaCO₃ crystallisation process to store and lock the carbon.

Using engineering biology, we’ll address the significant knowledge gap in the biochemical and molecular understanding of how templating proteins interact with inorganic ions, each other, or other biomolecules to control the carbon biomineralisation process and the CaCO₃ forms produced. We’ll also investigate their use in in vitro systems or engineered organisms to aid and accelerate carbon capture efforts and, in the process, generate value-added collateral.

Barriers

A primary risk of the project is the failure to identify templating proteins that successfully accelerate carbon biomineralisation, which we’ll mitigate by exploring proteins from many different organisms and protein families.

There are also challenges with scalability and regulatory requirements. For instance, the hydrogen protons released from the formation of unstructured CaCO₃ and by carbonic anhydrase leads to acidification of the reaction medium. This problem must be overcome to have net carbon sequestration, and also because the CaCO₃ formation process is more rapid at an alkaline pH. Moreover, it would limit the technology to controlled environments because acidification of water bodies can adversely affect native organisms. One way to deal with it is to engineer naturally nitrogen-fixing bacteria that live in microbialites, while another option is to perform the biomineralisation in purpose-built hypersaline/alkaline lakes, which are ideal for microbialite and stromatolite formation.

Success of the project also relies on limiting the amount of CO₂ produced by the process itself, however, there is room for this to be optimised and investigated in detail once a prototype process and technologies are available.

References

Iniesto et al. (2021). Rapid formation of mature microbialites in Lake Alchichica, Mexico. https://pubmed.ncbi.nlm.nih.gov/34396701/

Mass et al. (2013). Cloning and characterization of four novel coral acid-rich proteins that precipitate carbonates in vitro. https://pubmed.ncbi.nlm.nih.gov/23746634/