Bacteria engineered to eat carbon dioxide :Turn bacteria into biological factories for energy and even food.

Researchers have developed a strain of the bacterium (Escherichia coli) that grows by consuming carbon dioxide, rather than sugars or other organic molecules.

The achievement is a breakthrough, because it extremely alters the inner workings of one of biology’s most fame model organisms. In the future, CO2-eating E. coli could be used to make organic carbon molecules which can be used to produce food or as biofuel. Such products would have lower emissions compared with conventional production methods, and could conceively remove the gas from the air. The study was published in Cell1 on 27 November.

“It’s like a metabolic heart transplantation,” says Tobias Erb, who is a synthetic biologist and Biochemist at the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany. He wasn’t involved in the study.

Ron Milo, a systems biologist at the Weizmann Institute of Science in Rehovot, Israel, and his team have worked for over 10 years overhauling diet of E. coli. In 2016, they created a strain that consumed CO2, but the compound accounted for only a fraction of the organism’s carbon intake — the rest was an organic compound that the bacteria were fed, called pyruvate.

In the latest work, Milo and his team created a strain of E. coli by using a mix of genetic engineering and lab evolution. It can get all its carbon from CO2. First, they gave the bacterium genes that encode a pair of enzymes that allow photosynthetic organisms to convert CO2 into organic carbon. Plants and cyanobacteria power this conversion with light, but that wasn’t feasible for E. coli. Instead, Milo’s team transfer a gene that allows the bacterium get energy from an organic molecule known as formate.

Plants and photosynthetic cyanobacteria (aquatic microbes that produce oxygen) use the energy from light to transform, or fix, CO2 into the carbon-containing building blocks of life, including DNA, proteins and fats. But it is really harder to engineer these organisms, which has slowed efforts to transform them into biological factories.

By contrast, E. coli is relatively easy to engineer, and its fast growth means that changes can be quickly tested and tweaked to optimize genetic alterations. But the bacterium usually consumes sugars like glucose — instead of consuming CO2, it emits the gas as waste.

Even with these additions, the bacterium refused to change itts feed from sugars to CO2. For this purpose scientist further engineered the strain. The researchers cultured successive generations of the modified E. coli for one year, giving them only small quantities of sugar, and CO2 at concentrations about 250 times those in Earth’s atmosphere. They hoped that the bacteria would evolve mutations to adapt to this new diet. After about 6 months period, the first cells are produced which are capable of using CO2 as their only carbon source. And after 10 months, these bacteria grew faster in the lab conditions than normal(those which does not consume CO2).

The CO2-eating, or autotrophic, E. coli strains can still grow on sugar — and would use that source of fuel over CO2, given the choice, says Milo. Compared with normal E. coli, which can double in number every 20 minutes, the autotrophic E. coli are laggards, dividing every 18 hours when grown in an atmosphere that is 10% CO2. They are not able to subsist without sugar on atmospheric levels of CO2 — currently 0.041%.

Milo and his team hope to make their bacteria grow faster and survive on lower levels of carbon dioxide. They are also trying to understand how the E. coli evolved to eat CO2. Alterations in just 11 genes seemed to be enough to allow the switch, and they are now trying to figure out -how?.

The work is a “milestone” and shows the power of melding engineering and evolution to improve natural processes, says Cheryl Kerfeld, a bioengineer at Michigan State University in East Lansing and the Lawrence Berkeley National Laboratory in California.

Formerly, E. coli is used to make synthetic versions of useful chemicals such as human growth hormone and insulin. Milo says that his team’s work could expand the products that bacteria can make, to promote the use of renewable fuels, food and other substances. But he doesn’t see this happening soon.

“This is a proof-of-concept paper,” says Erb. “It will take a couple of years until we see this organism applied.”

Reference link :
1. Gleizer, S. et al. Cell.