Introduction

In 1796, an English doctor named Edward Jenner developed the first ever vaccine by exposing children to cowpox. Fast forward to 2023; a genetically engineered yeast expressing malaria proteins is being mass-produced as the world’s first ever viable malaria vaccine with more than 80% efficacy in children. In the 1920s, more than two tonnes of pig organs needed to be harvested to extract just 200g of insulin. But since the 1970s, genetically engineered E. coli has enabled industry to bring the cost of this essential drug to a price as low as $0.20-$0.60/day. Genetically modified grain crops in the last 20 years have increased global production of corn by 357 million tonnes. All over the world, there is an advancement in standards of living owed directly to this particular field of research. This is the story of synthetic biology.

Synthetic biology or ‘synbio’ broadly describes the engineering of genetic material that forms the coded instructions for living organisms, often resulting in the production of an enzyme or a molecule of interest.

Today, one of the greatest existential threats of our time is the problem of climate change. Here, we will attempt to describe why carbon capture technologies commonly face an inherent energy problem that is often misunderstood and why synthetic biology may give us an unparalleled advantage in solving some of these fundamental bottlenecks to mass-scale carbon sequestration.

Entropy is the unspoken obstacle for scaling carbon capture

We emit 41 billion tonnes of CO2 into the atmosphere each year of which less than 0.1% is removed by carbon capture. The latest Intergovernmental Panel on Climate Change (IPCC) targets for 2030 dictate that net emissions must fall by a staggering 43% to stay on track for 1.5°C warming.

To capture CO2 from the air with available sorbent technologies can cost anywhere between $250-600/T CO2 and anywhere between 1700-2400 kWh/T CO2. To truly understand why removing carbon from the atmosphere is so challenging, we must first understand the law of physics that presents the problem.

Entropy describes the disorder or randomness in a system. The second law of thermodynamics states that for decreasing entropy, an energy penalty must be paid in order to transfer a system from a state of high to low randomness. Just as energy is required to assemble a sand castle (low entropy) from the individual grains in a disordered heap of sand (high entropy), the same is true for the act of turning atmospheric CO2, present at 0.04% concentration, into 100% stream. There is, therefore, a calculable theoretical minimum energy needed to remove CO2 from atmospheric concentrations to overcome the entropy alone – which according to this law, amounts to 140kWh per tonne of CO2. However, since systems can only reach an estimated 10% of the thermodynamic efficiency, the practical minimum energy cost of overcoming this is widely estimated to be a minimum of 1400kWh.

This is not a widely discussed topic in the climate space. The problem of entropy is not merely how much carbon capture would cost financially to scale this to what would be required to meet IPCC targets. The crux of the issue is that the energy consumption required by the process itself, in the majority of places in the world today, would produce CO2 of a quantity that equates to more than 50% of the CO2 that has been captured from the process. All carbon capture technologies are an uphill battle against the natural direction of entropy. Biological systems, on the other hand, offer an unparalleled difference in the efficiency of its approach.

If it is true that all reactions in time favour the overall direction of increasing entropy, then living organisms, by definition, may at first, appear to contradict the second law of thermodynamics. This paradox was famously articulated in the 1944 book ‘What is life?’ by Nobel Physics laureate, Erwin Schrodinger. All natural organisms possess mechanisms by which they take energy from their surroundings to perform biochemical reactions that lead to order and physical structure, that ultimately is a state of thermodynamic disequilibrium with its environment. To do this, biological systems are, by necessity, forced to find the most energetically favourable way to perform these reactions all the way down to the molecular level. This is why it is much more favourable to make synthetic compounds with living systems.

Biological systems by nature seek what is energetically most efficient

CO2 has an extremely low enthalpy of formation – meaning that the conversion of CO2 into fuels, biomass, or almost anything that can conceivably be produced from it, requires an unavoidable energy penalty associated with this change. Carbon capture cannot simply be a process that ends at the collection of CO2 into a pure stream – this would be merely a filter. It must go beyond. For pragmatic reasons and economic viability, it must convert carbon into either a usable product or a low-volume substance that can be buried, both of which invariably require enthalpy change. But biology already does this to survive.  

Nature’s most powerful carbon capture machine comes in the form of an ancient single-celled organism called cyanobacteria. These marine organisms produce 30% of all the oxygen in the world. Inside these cells exists an intricate biochemical machinery that possess untold potential in the real world. The cell constructs an icosahedral structure inside itself called a carboxysome and densely packs an enzyme called Rubisco that reacts with CO2. Microscopic light-harvesting complexes (LHCs) that are found inside the thylakoid of cyanobacteria are being extensively studied to advance our understanding of photovoltaics. These proteins composed only of organic matter, are capable of harvesting light energy to produce a powerful electrochemical potential energy that powers the rest of the cell’s functions including the Calvin-Benson cycle which sequesters CO2.

Typical solar panels have a quantum efficiency (QE) of 19%; which means that almost 1 in 5 photons that lands on the doped silicon is converted into electrons. The most advanced commercially available systems of the last decade boast QEs of 26%. In contrast, the QE of the LHC in cyanobacteria that harvests light energy to capture carbon is 84-91%.  Because nature has already worked around the principles of thermodynamic feasibility, using photosynthetic microorganisms as a chassis for mass-scale carbon capture holds unparalleled potential. Synthetic biology simply enables us to further improve what is already a highly efficient machinery, create more of these systems, or permit a perpetual activation of it by controlling its expression.

Synthetic biology can valorise any captured carbon into downstream products

In many countries, the ability of a carbon capture technology to valorise its captured CO2 from the process is not a mere desirable, but a matter of commercial viability. Whilst the US and EU offer generous subsidisations and cap-and-trade mechanisms by which carbon capture is incentivised, in most countries globally, the carbon market is non-existent. If the captured CO2 has no additional downstream value, or worse, if there is no infrastructure in place for the storage of the captured CO2, this presents a major geographical constraint on where the technology can be deployed.  Synthetic biology overcomes this limitation.

Several companies have engineered organisms to convert captured carbon dioxide into high value compounds from omega-3 to construction materials even prior to the advent of advanced molecular techniques. But recent tools such as CRISPR-Cas12a have made it easier to engineer entirely new metabolic pathways inside cells; thus, no longer limited to a handful of gene insertions to achieve a desired function, but having more sophisticated biochemical reactions spanning several reaction steps. When applied to climate tech, we may soon see a paradigm shift, where complex molecules such as pigments or medical drugs can be produced from the CO2 out of a power station – only using sunlight to power the process.

Synthetic biology is affordable and scalable

Biological systems are built on organic matter – the bulk of the elemental composition being carbon, hydrogen, oxygen, nitrogen. There is little need for rare earth metals or the need to build impressive feats of architectural complexity to house the chemical reactions of interest on a large scale. Bacterial cells possess an extraordinary ability to reproduce exponentially while synthesising the molecule of interest with some carbon-fixing photosynthetic bacteria boasting doubling times of less than 2.5 hours given the right conditions. Even the most primitive single-celled life forms exhibit complex methods of controlled damage recognition and self-repair.

The major challenge is understanding the tight regulatory mechanisms that govern the cell’s physiology, which responds to even the finest changes in its environment. While synthetic biology has advanced over the decades in other organisms such as saccharomyces and E. coli to the point that we are able to computationally model its cultivation with extraordinary precision, we are yet to truly understand the large-scale cultivation of photoautotrophic bacteria as it is a nascent field in comparison. We are hopeful that such challenges can be overcome, accelerated by the abundance of molecular biology techniques available at hand only in recent years. Engineering organisms to capture carbon may be a challenge; however we are often reminded in this field that the bulk of the hard work is already done – we need not reinvent the wheel. The pursuit of biological research, both humbling and encouraging at times, often makes us wonder at the intricate systems that far exceed even the loftiest of imaginations of what is possible through human creativity. Therefore, we remain hopeful; perseverant with a kind of rational optimism that we will one day be able to engineer a carbon capture technology that will be made accessible to everyone by synthetic biology.

By

Dr David Kim, Founder of CyanoCapture – a biotech company that began at the University of Oxford