By: Israh Ghobbar
E. coli, short for Escherichia coli is a rod-shaped bacterium. It is a normal component of the intestinal bacterial flora, but under certain conditions, it can cause infections like gastroenteritis. E. coli’s genome can easily be manipulated by scientists to carry out a variety of functions, including consuming CO2.
Ron Milo, a biologist at the Weizmann Institute of Science in Rehovot, Israel and his team have spent a decade biologically modifying E. coli, so it grows by consuming carbon dioxide instead of sugars or other organic molecules. The process, known as metabolic rewiring, helped transform the diet of the e. coli, so it becomes similar to the diet of a plant. This involved adding genes which metabolise CO2 and removing genes which usually process sugar compounds. The cell turns autotrophic from heterotrophic after being modified, with autotrophic referring to organisms that can produce their own food from the substances available in their surroundings. Heterotrophs cannot synthesize their own food and rely on other organisms, both plants and animals for nutrition.
They created a strain that consumed CO2, but the compounded accounted for only a fraction of the organism’s carbon intake, the rest was an organic compound that the bacteria were fed, called pyruvate. Then 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, which couldn’t be done with E. coli. Instead, these scientists inserted a gene that allowed the bacteria to obtain energy from an organic molecule called formate. However, this was unsuccessful and was modified further by supplying the strain with minimal quantities of sugar and CO2 at concentrations 250 times more than those in the Earth’s atmosphere, with the hope that the bacteria would evolve mutations to adapt to this new diet. They observed that after 200 days, the first cells capable of only using CO2 as their only carbon source emerged and after 300 days these bacteria grew faster in the lab conditions than those that did not consume CO2.
Disadvantages include that e. coli strains can still grow using sugar and would favour this source of fuel over CO2, if given the choice. Compared to normal e. coli which can double in number every 20 minutes, the autotrophic e. coli is slower, dividing every 18 hours when grown in an atmosphere that is 10% CO2. This means they are not able to survive without sugar on atmospheric levels of CO2, which is currently 0.041%. Another disadvantage is the bacteria currently release more CO2 than is consumed through carbon fixation, meaning more research is needed before it is possible to discuss its industrial application.
Contrary, this discovery has many applications in science and society including the synthetic versions of useful chemicals such as insulin and human growth hormone which can be produced by the CO2 released as a by-product of the steel or concrete industry. E. coli that can consume CO2 could be used to make organic carbon molecules which could be used as biofuels or to produce food by improving the molecular machines to increase yields in agriculture. Researchers say their aim is to supply energy through renewable energy and use these genetically modified bacteria to address the issue of global warming.
According to other scientists including Cheryl Kerfeld, a bioengineer at Michigan State University in East Lansing and Lawrence Berkeley National Laboratory in California, this work shows the power of melding engineering and evolution to improve natural processes. Ron Milo and his team are continuing to investigate how e. coli evolved to consume CO2 after making changes to 11 genes, to make these cells more efficient and suitable for use in the future.
(Credit: Glezier et al.)