Is there a future where synthetic biology allows for household carbon fixation?
Exploring the current state of where we are at with carbon fixation, and diving in to what the potential future could look like...
It’s nearing 6pm, the sun is setting, and your day is coming to a close. You rush home from work just in time to feed your walls and windows.
Yes, you read that right.
Is there a reality where relieving your ecological footprint is as simple as keeping your walls and windows alive? Your very own household cyanobacteria or algae forming the photosynthesising heart of your living home, would be one of billions of households forming the collective carbon sinks on Earth. Is it possible? A future where anthropogenic activity relieves climate pressures instead of burdening it?
We have less than 8 years left to reduce global emissions by 50% if we want to achieve net-zero by 2050.
Now that you’ve imagined it briefly, let’s take a step back from this solar punk fantasy and see where we are at today. The not so obvious immediate answer to carbon fixation has been a reality for the past 500 million years. Plants are earth’s natural carbon fixers, converting atmospheric carbon dioxide into oxygen and glucose. Growing more trees and plants might be what you were initially thinking would underpin a future bioeconomy of household-based carbon capture. This refers to plant-mediated sequestration of CO2 which is then converted to biofuels in the form of plant biomass, or burned to generate energy. This is called, bioenergy with carbon capture and storage (BECCS).
The issue with solely relying on plants for carbon fixation is that they contain the world’s most inefficient enzyme, RuBisCo, which is roughly 90% less efficient than the average enzyme. This means that photosynthesis, the process controlling carbon fixation, is extremely slow. Countless scientists have already committed to the research challenge of improving the efficiency of RuBisCo. Its highly evolved structure and function are extensively conserved across diverse organisms, rendering it a poor candidate for genetic engineering. Plants are also slow-growing, making them even worse genetic engineering candidates. This creates a bottleneck for improving carbon fixation biotechnology.
Nonetheless; recent advances in plant genetic engineering have continued to push the field forward. San Francisco-based biotech startup, Living Carbon, claim to have developed a platform for enhancing photosynthesis - developing tree varieties that can accumulate 53% more biomass than control seedlings. The platform is said to be transferrable to other tree species as well. Living Carbon has already implemented several reforestation projects on undervalued land, being one of the first genetically modified trees to be grown in the wild.
Without significant improvements to photosynthesis, relying on BECCS as a means for tackling the climate crisis is insufficient. To limit global warming to 1.5ºC, 6% of current atmospheric CO2 would need to be sequestered. You would have to plant 1 trillion trees, and this would require over 2 billion acres, which is the equivalent to the total land area of the United States! Naturally, then you have the subsequent controversy of land use – deciding on choosing to prioritise land for reducing emissions or for feeding the world…
If only there were photosynthetic organisms that grew faster than plants and at microscopic scales requiring less space and fewer resources! Well, that is exactly where bio-based carbon capture technologies are at today.
Cyanobacteria can be used for the production of value-added chemicals and are more sustainable to grow, requiring less nutrients than bacteria – only water, CO2, and light, no need for sugar which requires vast amounts of land. The future of carbon capture lies in the hands of microscopic photosynthetic organisms such as cyanobacteria and their potential for being genetically engineered. With the ability to fix CO2 at rates up to 50 times greater than terrestrial plants, thus growing faster, this renders them more favourable for genetic engineering. The problem however lies in their doubling times - ranging from 2 up to 12 hours, this is still considered a bottleneck when working with cyanobacteria compared to faster growing species of bacteria. The future potential of photosynthetic microorganisms in supporting the bioeconomy will depend on the available synthetic biology tools for gene editing, which although are growing, are still not as developed as those used for more traditional microbes.
The challenge with carbon capture specifically at the household level, is that it’s quite the antonym to the scaled-up vision of industrialised processes. That does not mean it has less potential. Exploring household options for decarbonization would actually take on a completely new approach to scaling up biotechnology. An arguably more decentralised approach, where scaleup can refer to a collective contribution of households to the bioeconomy, as opposed to centralised conventional bioindustries.
So far, cyanobacteria have been used for producing food dyes and flavourings, as well as therapeutic biologic drugs, for example. Seeing as we are unlikely to need household sources of these valuable chemicals in the future, it seems that the more likely potential market for cyanobacteria lies in its use in construction. Unfortunately, there is currently a lack of overlap between synthetic biology and material sciences. Nonetheless, recent work is pushing this interdisciplinary field forward [1].
Self-healing bioconcrete is one potential application of cyanobacteria for carbon capture at the household level. Species of the genus Synechococcus are able to increase the binding between sand particles in a hydrogel matrix because they induce a process called biomineralisation [2]. In this process, the dissolved carbon dioxide in the water forms associations with the sand particles, thus creating a strengthened concrete-like material. This process is called microbially induced calcium carbonate precipitation (MICP). Indirectly, this would also reduce CO2 emissions, as traditional production methods of cement contribute at least 8% to global CO2 emissions. This biomineralised material was also able to regenerate up to three generations-worth of Synechococcus, making it a “self-healing”-like material [2]. Potential issues with this material include its mechanical competitiveness to conventional cement, however, there are ideas for how cyanobacteria could be engineered to overcome this, which includes expressing carbonic anhydrase, that will further crystallise the hydrogel-sand matrix.
The Hub for Biotechnology in the Built Environment based in Newcastle has been pioneering research in this field, investigating ways in which MICP can be incorporated into living construction materials. They are pushing the boundaries of what we can expect to see at the household level in the future, with a focus on carbon capture biotechnologies and modes of construction that aid the environment rather than burden it.
The other potential way in which cyanobacteria can be used at the household level is in biophotovoltaics, which is a biotechnology that converts solar energy into electrical energy using photosynthetic microorganisms [3]. Some cyanobacterial biofilms can produce an electrical photocurrent, which can be converted to electrical energy. It isn’t clear how well this competes with existing biofuel systems, but nonetheless, it is a technology with significant potential, and one that we hope to see in future households.
From where we are now to where we would like to be – that is, to seeing carbon capture implemented at a decentralised, household level – there is still a long way to go. Synthetic biology and interdisciplinary research have been and continue to be our main tools to getting us there.
We may not be close to a future where we are feeding our walls and windows, nonetheless, pioneering work in self-healing concrete, biophotovoltaics, and the growing momentum that exists in making cyanobacteria more suitable for genetic engineering, are all milestones that will bring us closer to a future where household carbon fixation may be possible. We also cannot forget the role that policy, education, and the community will have in the acceptance of these biotechnologies. Scientific knowledge isn’t the only barrier to household carbon capture. Other challenges include instilling robust technologies for biosecurity, always informing and ensuring transparency in the community in order to take a truly decentralised approach towards a future that benefits the environment rather than destroys it.
References
[1] Goodchild-Michelman IM, Church GM, Schubert MG, Tang T-C. Light and carbon: Synthetic biology toward new cyanobacteria-based living biomaterials. Materials Today Bio. 2023 Apr;19:100583. doi:10.1016/j.mtbio.2023.100583
[2] Heveran CM, Williams SL, Qiu J, Artier J, Hubler MH, Cook SM, et al. Biomineralization and successive regeneration of engineered living building materials. Matter. 2020 Jan 15;2(2):481–94. doi:10.1016/j.matt.2019.11.016
[3] Wenzel T, Härtter D, Bombelli P, Howe CJ, Steiner U. Porous translucent electrodes enhance current generation from photosynthetic biofilms. Nature Communications. 2018 Apr 3;9(1). doi:10.1038/s41467-018-03320-x