Rising atmospheric CO2 levels, attributed to human activities such as agriculture, have been a consistent topic of debate and research in the past few decades. To mark World Environment Day, our BioLabTests scientist looked at new research that promises to tackle climate change.
In an effort to reduce the harmful levels of the CO2 we emit, various damage limitation techniques have been implemented over the years. These include clean energy movements and encouraging dietary changes to mitigate the CO2 production from the farming sector. In addition to these large-scale techniques to reduce our CO2 output, some much smaller ones are currently being researched.
One microorganism that is playing a crucial role in this research is Escherichia coli. A recent research project looked at tackling climate change by converting E. coli to generate all biomass carbon from CO2.
A complete rewire
E. coli is a Gram-negative bacterium that is commonly used in research due to its rapid growth. E. coli is a heterotrophic organism, meaning that it consumes organic compounds. This type of organism is in contrast to autotrophs, which use CO2 to produce their biomass. A recent study from the Weizmann Institute of Science has managed to use directed evolution and alterations in metabolic pathways to facilitate the complete change in E. coli from a heterotroph to an autotroph.
The complete rewiring of E. coli, shown by this research, utilised the introduction of non-native enzymes to the bacteria. This approach allowed autotrophic growth in the experiment by expanding the metabolic pathways available to E. coli.
However, whilst the cells were now capable of autotrophic growth, the pathways utilised by E. coli could still be the default heterotrophic pathways. Therefore, the E. coli was grown in a growth medium that deterred the organism from using its natural pathways, giving the E. coli that were utilising the new autotrophic pathways a selective advantage.
Once the first evolved bacteria were identified, it was observed that the modified E. coli could survive on media when only supplemented with CO2 and an electron-donating agent called formate. To demonstrate that the carbon was solely coming from the CO2, meaning the the organism was now autotrophic, evolved E. coli was grown in the presence of isotopically labelled carbon. Results showed that biomass building blocks across the central metabolism of the bacteria had around 98% of their carbon labelled. This gave proof that the cells were producing biomass from only the CO2 and formate, proving that the cells were now autotrophic.
Offsetting CO2 emissions
The outcomes of this study show the early stages of what could become a powerful tool to combat climate change. The study also lays the foundations for future studies that wish to utilise the pliability of metabolic pathways in bacteria. The study did show that using formate led to a net CO2 production. However, this was attributed to the formate being oxidised to CO2 during the process.
It is proposed that in the future a renewable energy source could electrochemically produce an electron donor from CO2 with an overall negative greenhouse emission. The end use for this system would be to utilise lab-evolved bacteria to produce desired chemicals using only CO2 and an electron donor as an input into the system.
Modified bacteria, such as the one observed in this study, could be used on a large-scale to produce chemicals with formate derived from renewable energy. As the other input into the system is CO2, systems such as these would soak up a large quantity of atmospheric CO2, offsetting at least a small part of our CO2 emissions.
This study is an interesting concept and shows what could be possible in future. It requires further research to turn it into a potentially useful application that can help to tackle some of the biggest challenges of humanity today.