A more eco-friendly food supply could rely on E. coli
By Pippa Wysong
Could the proteins we usually get from meat and dairy be produced by bacteria instead? Could the same bacteria be altered to help extract carbon dioxide from the air? While this sounds like something out of science fiction, these are the very questions being investigated by Elad Noor, a computational analyst and metabolic engineer. Noor is an alumnus of the Azrieli Fellowship Program, and he conducted his research at the Weizmann Institute of Science.
As the global population continues to grow, new methods are needed to produce foods that keep up with demand while having a low environmental footprint. Using bacteria to produce the proteins and other nutrients in our diets could be one of the answers.
Currently, agricultural systems and food production have high environmental costs, including habitat loss, energy use and greenhouse gas emissions—especially from animal-based products. Generally, plant-based foods have a far smaller environmental footprint and lower energy usage than their animal-based counterparts, yet they provide similar nutrients.
This is where Noor comes in. Through his work at the MiloLab@weizmann in the Department of Plant and Environmental Sciences, he developed a computational model to identify ways to manipulate the metabolic pathways in E. coli bacteria. The purpose was to find more efficient ways for E. coli to conduct carbon fixation, or extract carbon for fuel. Instead of using sucrose or glucose as a carbon source, it could use carbon dioxide from the atmosphere. This may open the door to genetically engineering E. coli and other types of bacteria to use new pathways that facilitate more eco-friendly food production. Details of the work he conducted with eight other researchers can be found in “Awakening a latent carbon fixation cycle in Escherichia coli” (Nature Communications, November 2020).
Says Noor: “Bacteria that do more efficient carbon fixing as well as producing proteins could contribute to our food supply while helping us clean the atmosphere.”
Another approach that can contribute to a more sustainable future is to use cleaner substances to trigger chemical reactions for producing materials and chemicals. It is estimated that up to 90 per cent of all chemical processes, whether biological or industrial, require a catalyst. Finding new ones could save enormous amounts of energy and facilitate new chemical reactions that convert unsustainable waste streams to renewable resources.
“This is needed because humanity is at a critical juncture. The amount of human-made mass now exceeds all the available biomass on the planet. Most of this leads to emissions and pollutants that damage the environment,” says Graham de Ruiter, head of the Laboratory for Inorganic & Materials Chemistry at the Technion – Israel Institute of Technology. The Azrieli Early Career Faculty Fellow in chemistry is a native of the Netherlands who was drawn to living and working in Israel because of the warmth of the people and “the way they value research and harness intellectual advancement.”
In the lab, de Ruiter and his team are developing new catalysts that enable chemical reactivity in cleaner and more sustainable ways. Catalysts are substances that trigger and speed up chemical reactions. They are commonly used throughout industry; however, the processes are often toxic and overall unsustainable.
“It may not be the first thing on people’s minds, but where clean energy really starts is with catalysis.”
“It may not be the first thing on people’s minds, but where clean energy really starts is with catalysis,” de Ruiter says. “It all starts with a tiny molecule that is able to convert one molecule to another. And if you are able to control this, you have the future.”
Currently, metals belonging to the platinum group, especially palladium, rhodium and iridium, are widely used as catalysts because they are stable and lead to reactions that are predictable and safe. They are used to produce materials ranging from plastics and fertilizers to pharmaceuticals and specialty chemicals.
A commonly used reaction that involves a catalyst is the formation of carbon-carbon bonds, which are needed for a wide range of applications. Nature regularly makes carbon-carbon bonds using highly specialized enzymes (nature’s catalysts) that contain common metals, such as iron. In fact, the past decade has seen a surge of interest among chemical scientists in mimicking these processes.
These carbon-carbon bonds introduce—as chemists call it—chemical complexity, and they are a key component in developing new pharmaceuticals. An example is the production of eletriptan, a selective serotonin agonist used to treat migraines. Here, a palladium catalyst is used to make the carbon-carbon bonds necessary to create the chemical that forms the drug. However, mining the geological deposits that contain platinum metals generates high carbon footprints and destroys the ecological habitats in which they are found.
To find substitutes, de Ruiter and his team are investigating earth-abundant metals such as iron, manganese and cobalt. All three are common and cheap, and they have lower environmental footprints than the platinum metals. But one cannot simply replace palladium with iron. For one thing, these metals differ in their basic reactivity. So far, iron, manganese and cobalt haven’t done the job as predictably as platinum metals.
From a chemist’s point of view, “iron is like a teenager among the transition metals— it’s not mature and does whatever it wants. It is always difficult to control,” de Ruiter says, adding that to overcome this limitation, “we’re using nature and the way enzymes work as inspiration. We’re trying to take the design principles that we find in nature and apply them to chemical transformations that are of interest to industry and academia.”
One aspect of de Ruiter’s work is manipulating the chemical environment surrounding the metal ions, or ligands. Altering the electronic properties of the ion’s metal centre makes its chemical reactivity more predictable and reliable. In fact, his lab developed a new ligand system that successfully controls the reactivity of iron. The system can selectively replace hydrogen atoms with deuterium atoms in a hydrogen-deuterium exchange process. Deuterium, or hydrogen-2, is an isotope of hydrogen that is widely used as a non-radioactive tracer in the pharmaceutical industry, and de Ruiter’s system provides a cleaner way of producing it.
The team also developed an iron-based catalyst for the isomerization of alkenes—a process important in the chemical industry. Alkenes are hydrocarbons with double carbon-carbon bonds. Isomerization is a process in which part of a molecule is rearranged. The new catalyst lasts longer and works more efficiently than those using the platinum group metals.
“Some of the most active catalysts that do this are based on iridium. Each iridium catalyst can be used 19,000 times. But this new iron catalyst can be used 160,000 times, with the same general benefits seen from iridium,” de Ruiter says. The implications are that the amount of iron needed for chemical reactions is much lower, plus it lacks iridium’s toxicity. The findings will be published in a paper later this year.
Catalysts are used in such a wide range of industries that replacing standard platinum-metal catalysts with ones made from earth-abundant metals could go a long way towards conserving the environment and reducing carbon emissions.
Says de Ruiter: “This is really the pinnacle of sustainability.”