Synthetic Biology’s Answer to Climate Change

Climate change is a powerful force that has shaped the evolution of life on Earth. It has caused mass extinctions but has also created new opportunities for species to adapt and diversify. In fact, that’s how mammals were able to proliferate after dinosaurs were wiped out from the face of the Earth. However, climate change is distinctly human-induced this time, unlike past events due to natural causes like volcanic or meteoric activity. If we continue on this destructive path, risking the lives of countless species and disturbing ecological balance, the downfall of our species and planet will be solely due to our actions.

Climate change due to global warming slowly started around a century ago, but it has picked up a significant pace in recent decades. Today, widespread awareness about the Earth’s transformation exists around the world; even tribal people far from civilisation know that our planet’s atmosphere and biosphere are changing rapidly. The signs are everywhere; the rising global temperatures, melting of glaciers in the Arctic and Antarctic, rising sea levels, disruption in season cycles, etc., are all outcomes of global warming. Due to the recent development of theories like biocapacity and ecological or carbon footprint, we can quantify the damage being caused to the planet. We are currently using up resources of 1.6 Earths per year; in layman’s terms, we are using up resources 1.6 times faster than they are being replenished. In Climate Modelling, RCPs (Representative Concentration Pathways) are used to predict varying global scenarios according to emission trends. Our current emission trends point to RCP 8.5, which indicates an alarming rise in the average global temperature by around 4 °C, which can devastatingly impact terrestrial and marine ecosystems. Thus, it is high time we recognise our mistakes and take sustainable actions to mitigate this crisis.

The primary reason behind climate change is the harrowing rise in greenhouse gases in the atmosphere. Environmentalists and activists worldwide have been urging people to incorporate sustainable practices into their daily lifestyle, which have the potential to reduce global greenhouse gas emissions. There have been ongoing protests against big oil and gas companies and industries, which give rise to a significant amount of emissions. The use of technologies and alternative raw materials, which can decrease total emissions, are some of the changes people are asking them to implement. So far, the prevailing efforts of activists and advocating global leaders to subsidise environment-friendly resources and technologies have been the primary face of climate action. Nonetheless, ongoing research endeavours in synthetic biology promise to be eco-friendly as well as profitable, if proven successful.

Decoupling economic growth from increased fossil fuel consumption is the first step towards reducing carbon dioxide emissions. To achieve this, scientists have created biofuels that can provide a viable course of action. Biofuels are developed by engineering the genome of microorganisms to convert non-edible, renewable carbon sources like lignocellulosic sugars into ethanol, offering a sustainable alternative to fossil fuels. However, emissions are not entirely eliminated as chemoorganotrophic microbes like yeast or E. coli release carbon dioxide during fermentation in bioreactors as part of their carbon metabolism. Additionally, these biofuels produce carbon dioxide upon combustion, but emissions are significantly lower than conventional fossil fuels. Hence, researchers are investigating the potential of autotrophic microorganisms like acetogenic anaerobic bacteria and microalgae, which can capture and utilise atmospheric carbon dioxide in their metabolic processes. Naturally, these reactions are prolonged and have low energy conversion yield; synthetic biology makes them industrially efficient by rewiring their carbon metabolism network to optimise carbon conservation or recapturing carbon loss using carbon dioxide fixation or carboxylation systems.

A few of such modified metabolic pathways in heterotrophic microorganisms for carbon dioxide utilization and greater carbon conservation efficiency are-

• the Non-Oxidative Glycolysis (NOG) pathway (Bogorad et al., 2013), which can overcome the 33% carbon loss in the glycolysis pathway; Pentose-Bifido-Glycolysis cycle to solve the lack of reducing power in the NOG;
• the Glycoptimus Pathway to convert sugars into glycolic acid without carbon loss; the Methanol Condensation Cycle for methanol assimilation without carbon loss;
• reversal of the Glyoxylate Shunt to build C2 compounds with maximal carbon conservation;
• modification of the serine cycle in E. coli, which is a natural pathway to assimilate C1 carbon such as methanol or methane into acetyl-CoA intermediate without loss of carbon;
• HOB pathway, which is an alternative to C1 carbon metabolism through carbon dioxide fixation by PEP carboxylase;
• In-situ reintegration of carbon dioxide into the central metabolic network by incorporating Calvin-Benson Cycle enzymes.

Another strategy scientists have employed is modifying microbes to produce different chemical commodities by using various air pollutants and greenhouse gases like carbon dioxide. These microbes absorb more greenhouse gasses than they release, so this method has been termed carbon-negative manufacturing. Such a class of autotrophic bacteria is Acetogens, which live on carbon dioxide and produce complex organic substances. Efforts to engineer acetogens to make them more efficient and alter their metabolic pathways so we can get byproducts according to our needs are underway — for example, Clostridium autoethanogenum.

Carbon-negative synthetic biology has also seen much progress in efforts to use cyanobacteria for environmental carbon dioxide sequestration. Apart from yeast and E. coli, cyanobacteria is also considered a viable chassis for engineering carbon-negative synthesis pathways. Cyanobacteria has already been used to produce many value-added products, such as squalene, α-farnesene, limonene, ethylene, resveratrol, p-coumaric acid, caffeic acid, and ferulic acid, directly via carbon capture. Cyanobacteria are also being engineered to develop biodegradable plastics, a great plus point from an environmental perspective. Thus, autotrophs like cyanobacteria and acetogens are not only helping to reduce carbon dioxide but also facilitating the production of eco-friendly products. An illustrative example is a bacteria that generates proteins that can substitute fish in fishmeal, utilising atmospheric carbon dioxide. This approach not only aids in reducing atmospheric CO2 but also minimises the demand for fish.

Another notable research area that aims to sequester and degrade certain environmental pollutants, other than greenhouse gases, is the development of bacteria with enzymes that degrade PET (Polyethylene terephthalate) and other non-biodegradable waste, which can be utilised for recycling or breaking down waste at source.

An essential part of climate action is environmental decontamination, i.e., removal of pollutants. Bioremediation is a process wherein genetically modified microbes are employed to decontaminate soil or water. These microbes use pollutants for energy, break down organic compounds, and absorb inorganic substances. One such innovation in marine bioremediation is the development of synthetic jellyfish capable of absorbing and neutralising toxic chemicals in marine environments, especially after poisonous spills. These jellyfish are engineered to prevent replication and are programmed to self-destruct after a specific period. Though still in developmental stages, these multicellular engineered organisms hold considerable promise for future marine ecosystem restoration.

Lastly, even if climate change becomes irreversible, synthetic biology has the potential to create engineered crops and other food sources that can withstand harsh climatic conditions. But our collective responsibility should be to prevent this dire day from dawning upon humanity. Synthetic biology holds immense potential that is slowly being unlocked. Still, we should only use these resources responsibly with proper testing and failure proof. Otherwise, dire situations like genetic contamination of wild gene pools, extinction of species, and even the advent of new genetic diseases in humans or other organisms might occur, which will be fatal for the ecosystem.

Despite the crippling effects of global warming on the global climate, it remains a reversible change to date. As individuals, we are responsible for changing how we live and reducing our ecological footprint by consuming less energy and incorporating sustainable habits in our daily routines. Synthetic biology will enable us to easily achieve these goals in the coming decades by equipping ourselves with tools like emission-reductive biofuels and carbon dioxide-sequestering microbes, making carbon-negative synthesis possible. With combined efforts worldwide to live mindfully and consistent headways in synthetic biology innovations, we can finally revert climate change and restore environmental balance.

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