Enzyme-enhanced CO2 storage in rocks

Project duration: November 2024–June 2026

Project lead

Team

David Midgley, Nai Tran-Dinh, Linda Stalker, Anna Kaksonen.

Opportunity

Carbonic anhydrase (CA) is a powerful enzyme that plays a critical role in the carbon sequestration process. It functions as a super-fast molecular shuttle, accelerating CO₂ conversion up to one million times per second.

CA rapidly converts CO₂ and water into bicarbonate and hydrogen ions, essentially helping molecules move CO₂ around more efficiently in biological systems. This process, known as CO₂ hydration, paves the way for mineralisation. This is where captured carbon is transformed into stable carbonate minerals.

The carbonic anhydrases are a large and ancient group of enzymes. While they are widespread in plants, animals and bacteria, few of the CA family members have been described. We believe there is untapped potential of CAs with high potential to catalyse CO₂ hydration at even higher turnover rates.

CA biodiscovery for CO₂ mineralisation has seen significant advancements in recent years. Extremophilic microorganisms have emerged as promising sources of robust CAs. Thermophilic and alkaliphilic microbes are of particular interest, as they may yield enzymes capable of withstanding harsh industrial conditions. Heat-stable CAs from bacterial, archaeal, and fungal origins have been identified and patented for use in CO₂ extraction from flue gases, biogas, and natural gas at elevated temperatures.

Improving our understanding of CAs could aid in the development of more efficient in-situ mineral carbonation technologies. These technologies involve a process where CO₂ is chemically reacted with calcium- and/or magnesium-containing minerals to form stable carbonate materials. Currently, mineral carbonation technologies face efficiency and cost challenges associated with ongoing storage liabilities of underground CO₂ storage sites (up to hundreds of years). This research could help improve the long-term monitoring and maintenance requirements at storage sites.

Goal

This project aims to identify natural CA variants that that can outperform equivalent currently-studied versions in their carbon sequestration potential.

By exploring the full evolutionary diversity of the CA enzyme, we will seek to develop more robust and stable enzymatic systems. This could help overcome one of the major hurdles in enzyme-based mineral carbonation technologies: poor stability under industrial conditions.

It could also present a more environmentally-friendly alternative to conventional amine solvent-based CO₂ capture technologies, which can have negative environmental impacts and high energy requirements for regeneration.

This project will consist of three stages:

• Phase 1: Bioinformatics Analysis, Field Work, and Screening (Months 1-6)
• Phase 2: Gene Identification and Expression (Months 6-13)
• Phase 3: In Vitro CO₂ Mineralisation Studies (Months 13-24)

Barriers

Maintaining enzyme stability in our cultures will likely be challenging when replicating biomineralisation conditions. These include high temperatures, alkaline pH, and in the presence of inhibitors commonly found in industrial settings. Scaling up enzyme production for industrial-scale applications also remains a significant hurdle.

We will use various mitigating strategies to overcome these barriers, including bioprospecting in extreme environments, employing protein engineering techniques, and developing high-throughput screening methods to efficiently evaluate the performance of various CA isoforms. And we’ll shift focus to other environments where the microbiotia may be more amenable. We will explore alternative screening methods as a last resort.

If we are successful, we anticipate the project could create opportunities such as:

1. Enhanced carbon capture technology: The discovery of novel, highly efficient prokaryotic CAs could speed-up carbon capture and storage technologies. These enzymes can catalyse CO₂ hydration several magnitudes faster than the uncatalysed reaction, potentially enabling more rapid and efficient CO₂ mineralisation processes.
2. Biomimetic carbon sequestration industry: The project could spark a new industry focused on enzyme-assisted CO₂ mineralisation, mimicking and enhancing natural weathering processes for long-term carbon storage.
3. Sustainable construction materials: CA-assisted mineralisation could lead to the development of carbon-negative construction materials, creating new opportunities in the building industry. The resulting carbonate minerals could be used in cement, chemicals, fillers for paper making, and other construction materials.
4. Specialised enzyme production: Biotechnology companies could emerge, focusing on large-scale production of the most efficient prokaryotic CAs for carbon capture applications.
5. Environmental remediation services: New businesses could offer specialised CO₂ mineralisation services using the discovered enzymes, creating a sector in environmental remediation and carbon offsetting.
6. Mining and mineral processing: The project could lead to innovative processes for extracting valuable minerals from CO₂-rich waste streams, potentially reinventing aspects of the mining and mineral processing industries.

References

Bose, H., & Satyanarayana, T. (2017). Microbial carbonic anhydrases in biomimetic carbon sequestration for mitigating global warming: prospects and perspectives. Frontiers in microbiology, 8, 1615.

Power, I. M., Harrison, A. L., & Dipple, G. M. (2016). Accelerating mineral carbonation using carbonic anhydrase. Environmental science & technology, 50(5), 2610-2618.

Smith, K. S., Jakubzick, C., Whittam, T. S., & Ferry, J. G. (1999). Carbonic anhydrase is an ancient enzyme widespread in prokaryotes. Proceedings of the National Academy of Sciences, 96(26), 15184-15189.