05.16.2021

This Synthetic Bacteria Doesn’t Need Food To Grow, Only CO2

By Andrea D. Steffen

Synthetic biologists performed a biochemical switcheroo, re-engineering a bacterium that usually consumes a diet of simple sugars into one that constructs its cells by absorbing carbon dioxide (CO2) like plants. The work paves the way for engineered microbes that sequester CO2 out of the air and turn it into medicines and other high-value substances.

Dave Savage, a biochemist at the University of California, Berkeley, who was not a part of the ongoing work, said:

The implications of this are profound. [Such advances could] ultimately make us change the way we teach biochemistry.

Biologists typically separate the world into two kinds of organisms: autotrophs and heterotrophs. Autotrophs consist mainly of flowers plus some germs. They mostly use photosynthesis to convert CO2 into sugars and other organic compounds needed to create their cells. All other organisms, including we humans, gets those building blocks from the organisms they eat.

Synthetic biologists have long been trying to engineer plants and bacteria that are autotrophic to produce valuable chemical substances and fuels from water and CO2. The opportunity is appealing because of its potential to become cheaper than many other routes.

But, until now, scientists have only been successful at getting the heterotrophic Escherichia coli bacterium (E-coli) to produce ethanol and other desired chemical substances more cheaply. E-coli is known to most people as the microbe that lives in our guts and sometimes triggers food poisoning. However, these engineered E-coli strains must consume a constant diet, increasing the costs of the effort. So, most of the time it’s not cheaper.

Everything changed when synthetic biologist Ron Milo and his peers at the Weizmann Institute of Science in Rehovot, Israel, decided to see whether they could transform E-coli into an autotroph. To do so, they re-engineered two essential components of the bacterium’s metabolism: just how it gets power and precisely what supply of carbon it makes use of to develop.

The researchers couldn’t provide the bacterium the capability to conduct photosynthesis because the method is too complex on the energy part. Instead, the researchers inserted the gene for an enzyme that empowered the microbe to eat formate, one of the most basic carbon-containing compounds and one that other strains of E. coli can’t eat.

This Synthetic Bacteria Doesn't Need Food To Grow, Only CO2.
(Credit: Cell)

The modification allowed the microbes to transform the formate into ATP, an energy-rich molecule that cells can utilize. That diet gave the microbe the energy needed to use the second batch of enzymes it received. Three in all, the new enzymes enabled the microbe to convert CO2 into sugars and other organic molecules. The researchers also removed several enzymes the bacterium typically utilizes for metabolism, forcing it to rely on the new diet to grow.

However, the changes didn’t produce bacteria capable of living on formate and CO2 at first. The researchers suspected this to be because the nutritional elements were still being directed toward its natural metabolism. So, they placed batches of the engineered E-coli in vessels that allowed them to control the microbe’s diet meticulously.

The researchers started with a starvation diet of xylose (sugar) mixed with formate and CO2. This allowed the microbes to survive barely and still reproduce. It also laid out the groundwork for evolution: If any bacterial offspring underwent genetic mutations that allowed them to thrive on that diet, they’d produce more offspring than those that didn’t evolve.

The researchers also steadily reduced the amount of xylose available. After 300 days, the xylose was gone and what was left was a vast selection of generations of mutated E. coli. Only those bacteria that evolved into autotrophs survived. The team reported that the evolved germs picked up 11 new genetic mutations that enabled them to survive without eating other organisms.

Milo said:

It shows how amazing evolution can be, in that it can change something so fundamental as cellular metabolism.

Pam Silver, a Harvard systems biologist who was not involved with this study but devoted years to a similar project, said:

I bow to them for making it succeed.

Experts have developed many tools to manipulate E-coli’s genes to have it produce various compounds, such as pharmaceuticals and fuels. Now, researchers will be able to insert these noticeable modifications into autotrophic E. coli that eat formate.

Formate can be readily made by zapping CO2 in water with electricity. Because of this, sustainable formate (produced from wind and solar power) could be used to engineer bacteria to make ethanol and other things, including the malaria-fighting drug artemisinin.

This article appeared on the IntelligentLiving website at https://www.intelligentliving.co/synthetic-bacteria-co2/

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