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Not that way; this way

Can a living organism be obliged to take something other than its regular route for the synthesis of the molecules it needs to live and multiply? A team from the François Jacob Institute of Biology did just that, getting bacteria to assimilate CO2 in a new way.

Published on 18 September 2017
The development of green chemistry depends in part on the exploitation of the metabolic capacities of microorganisms. Enzymes catalyze, photosynthesizing organisms produce biomass, bacteria ferment—and scientists seek to understand and manipulate the metabolic pathways of these natural factories with the goal of creating sustainable industrial processes.

The researchers at the François Jacob Institute of Biology are no exception.  "We worked with the well-known bacteria Escherichia coli to transform one of the principal pathways for the metabolism of carbon," explains Madeleine Bouzon, researcher at the Institute. "The natural metabolic pathway in question takes carbon atoms from amino acids and transfers them to other pathways for the biosynthesis of compounds that are vital for the bacteria. For organisms like Escherichia coli, carbon atoms come from the sugars used as nutriment. We prompted the bacteria to use another pathway that fixes CO2 and assimilates it in these biosynthesis pathways."

In reality, the bacteria did not really have a choice. The team artificially suppressed the enzymes responsible for the transfer of carbon atoms by eliminating their coding genes. "In the beginning, the bacteria in the culture media were furnished with the compounds they were no longer capable of producing themselves," explains the biologist. "Thereafter, we continued cultivating them in progressively restrictive conditions. Little by little, as beneficial spontaneous mutations were selected, the Escherichia coli started getting by on their own."

It took the bacteria 720 generations (about four months), relatively few, in their progressively restrictive media to discover a new metabolic pathway for the assimilation of CO2. This directed in vivo evolution was possible thanks to Genoscope's automated continuous culture devices, which have a system to control bacterial density in the cultures via the flow of nutriments. "We blocked one metabolic pathway but left the bacteria free to find another. Going forward we hope to direct the bacteria in a specific direction so that they learn to produce biomass from formic acid," concludes Ms. Bouzon.

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