New synthetic metabolic pathways for fixation of carbon dioxide could not only help to reduce the carbon dioxide content of the atmosphere, but also replace conventional chemical manufacturing processes for pharmaceuticals and active ingredients with carbon-neutral, biological processes.
An Urgent Issue
In view of rising greenhouse gas emissions, carbon capture, the sequestration of carbon dioxide from large emission sources, is an urgent issue. In nature, carbon dioxide assimilation has been taking place for millions of years, but its capacity is far from sufficient to compensate man-made emissions. Researchers led by Tobias Erb at the Max Planck Institute for Terrestrial Microbiology are using nature’s toolbox to develop new ways of carbon dioxide fixation. They have now succeeded in developing an artificial metabolic pathway that produces the highly reactive formaldehyde from formic acid, a possible intermediate product of artificial photosynthesis. Formaldehyde could be fed directly into several metabolic pathways to form other valuable substances without any toxic effects. As in the natural process, two primary components are required: Energy and carbon.
Role Of Formic Acid
Within the added-value chain, the carbon source is variable. carbon dioxide is not the only option here, all monocarbons (C1 building blocks) come into question: carbon monoxide, formic acid, formaldehyde, methanol and methane. However, almost all of these substances are highly toxic—either to living organisms (carbon monoxide, formaldehyde, methanol) or to the planet (methane as a greenhouse gas). Only formic acid, when neutralized to its base formate, is tolerated by many microorganisms in high concentrations.
“Formic acid is a very promising carbon source,” says Maren Nattermann, first author of the study. “But converting it to formaldehyde in the test tube is quite energy-intensive.” This is because the salt of formic acid, formate, cannot be converted easily into formaldehyde. The researcher’s goal was to find a more economical way. After all, the less energy it takes to feed carbon into metabolism, the more energy remains to drive growth or production. But such a path does not exist in nature.
High Throughput Tech
The optimization of the enzymes included several approaches: building blocks were specifically exchanged, and random mutations were generated and selected for capability. “Formate and formaldehyde are both wonderfully suited because they penetrate cell walls. We can put formate into the culture medium of cells that produce our enzymes, and after a few hours convert the formaldehyde produced into a non-toxic yellow dye,” explains Maren Nattermann.
The result would not have been possible in such a short time without the use of high-throughput methods. To achieve this, the researchers cooperated with their industrial partner Festo, based in Esslingen, Germany. “After about 4,000 variants, we achieved a fourfold improvement in production,” says Maren Nattermann. “We have thus created the basis for the model mikrobe Escherichia coli, the microbial workhorse of biotechnology, to grow on formic acid. For now, however, our cells can only produce formaldehyde, not convert it further.”
Did you subscribe to our Newsletter?
It’s Free! Click here to Subscribe!