Scientists use evolution to design new paths to sustainable energy and pharmaceuticals

Using evolution as a guiding principle, the researchers were able to create bacteria-yeast hybrids that can assimilate carbon through photosynthesis, generate cellular energy, and support yeast growth without the use of traditional carbon feedstocks such as glucose or glycerol. By creating photosynthetic cyanobacteria that can live symbiotically inside yeast cells, the bacteria-yeast hybrids can produce important hydrocarbons, opening the way to new biotechnological pathways to non-petroleum energy, other applications of synthetic biology, and the experimental study of evolution.

“All cells with a nucleus also harbor a variety of organelles, such as mitochondria and chloroplasts, that perform specific functions and contain their own DNA,” said Angad Mehta, a professor of chemistry at the University of Illinois at Urbana-Champaign who led the Illinois research team. “Researchers have long hypothesized that complex life forms arise when one of these cell types fuses with another in a process called endosymbiosis.”

In a previous study, Mehta’s team showed that lab-generated cyanobacteria-yeast chimeras, or endosymbionts, can provide photosynthetically generated ATP to yeast, but do not provide sugars. In the new study, the team engineered cyanobacteria to break down sugars and secrete glucose, then combined them with yeast cells to create chimeras that can grow in the presence of CO₂using the sugar and energy produced by the bacteria.

The results of the new study are published in the journal Nature Communications.

Armed with the ability to transform a non-photosynthetic organism into a photosynthetic chimeric life form, the team focused their research on determining how these chimeras could be used to create new metabolic pathways capable of producing valuable products such as limonene, a simple hydrocarbon compound found in citrus fruits, under photosynthetic conditions.

“Limonene is a relatively simple but important molecule that has a large market,” said Mehta, who is also affiliated with the Carl R. Woese Institute for Genomic Biology. “This proof-of-concept study shows us that we can design pathways in our hybrids to photosynthetically produce limonene, which belongs to a class of molecules called terpenoids, which are also precursors to many high-value compounds such as fuels, anticancer drugs and antimalarial drugs.”

Mehta said their goals for this line of research are to determine whether their method can produce more complex compounds, such as fuels and pharmaceuticals, and if so, to work toward scaling the process up to make it commercially viable.

“I think it would be incredible to get to the point where we could guarantee that every single carbon particle in a high-value compound came from CO₂“, Mehta said. “This could be a way to recycle CO₂ “Waste in the future.”

The team also said that in its quest to understand and refine endosymbiotic systems to advance biotechnology, it will also answer many fundamental evolutionary questions along the way.

“It’s going to happen whether we want it to or not,” Mehta said. “We’re always keeping an eye on how our work can answer some of the mysteries of the evolution of life. In my opinion, the best way to design endosymbiotic systems will be to recreate the process of evolution in the lab. Finding answers to some of the biggest questions in biology will come naturally.”

Illinois researchers Yang-le Gao, Jason Cournoyer, Bidhan De, Catherine Wallace, Alexander Ulanov and Michael La Frano also participated in the study.