Improving microbial memory to better recycle excess CO₂

While some microbes can make people sick or spoil food, others are essential to survival. These tiny organisms can also be engineered to produce specific molecules. Researchers report in ACS Sustainable Chemistry and Engineering have reprogrammed one of these microbes to help combat greenhouse gases in the atmosphere: it absorbs carbon dioxide (CO₂) gas and produces mevalonate, a useful building block for pharmaceuticals.

The increasing concentration of greenhouse gases in the atmosphere has led to widespread global warming. To begin to address the problem, greenhouse gas emissions, particularly CO₂must be significantly reduced. In addition, CO₂ already present could be deleted.

CO capture methods₂ Research is ongoing, and one of the most promising options involves microbes. Genetic engineering can alter their natural biosynthetic pathways, turning microbes into miniature living factories capable of producing all sorts of things, like insulin.

Cupriavidus necator H16 is a bacterium that could be a microbial factory, as it is relatively undemanding about what it is fed. In fact, it can survive on little more than CO₂ and hydrogen, the bacteria is a great candidate for capturing and converting the gases into larger molecules. But while the microbe’s DNA can be reprogrammed to produce interesting products, it’s not very good at remembering those new instructions over time.

To put it scientifically, plasmids (genetic instructions) are relatively unstable. Katalin Kovacs and her colleagues wanted to see if they could improve C. necator’s ability to memorize its new instructions and produce useful carbon-based building blocks from CO₂ gas.

The team set to work hacking C. necator’s biochemical pathways responsible for CO conversion₂ into larger six-carbon molecules. The key to improving plasmid stability lies in an enzyme called RubisCo, which allows the bacteria to use CO₂.

In fact, the new plasmid was coupled to the enzyme, so that if a cell failed to memorize the new instructions, it would fail to remember how to make RubisCo and would die. Meanwhile, the remaining cells, with better memories, would survive and replicate, passing on the plasmid.

In tests, the newly created microbes produced significantly more mevalonate, a six-carbon molecule, than a control strain. Mevalonate is a molecular building block for all sorts of substances in living and synthetic systems, including cholesterol and other steroid molecules with pharmaceutical applications. In fact, this research produced the largest quantities to date of mevalonate from CO₂ or other single-carbon reagents using microbes.

The researchers say it is a more economically viable carbon fixation system than previous systems involving C. necator, and could also be extended to other microbial strains.