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Easy artificial evolution makes for solar-powered yeast

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Easy artificial evolution makes for solar-powered yeast

Scientists have given yeast a brand new ability – gaining energy from light. The technique was remarkably easy, the team says, and could not only help us understand evolution but make better beer and biofuel.

As any amateur brewer or baker will tell you, yeast is very sensitive to light. Exposure will kill it off, leaving your bread or beer flat. The stuff grows and works best in total darkness and under careful temperature control, but in a new study, scientists at Georgia Tech have engineered yeast to not only survive but thrive in the light.

The researchers edited the genes of the yeast to turn it into a phototroph – an organism that captures light and uses it to produce energy. Plants of course are the most famous examples, but others include algae and some types of bacteria. Most of the time, the ability comes about through complicated molecular machinery, which would be too cumbersome to insert into an organism that doesn’t have the proper genetic context.

For the new study, the team gave the yeast a much simpler tool – proteins called rhodopsins, which convert light into energy on their own. Not only are they self-contained, but the genes for them are naturally readily passed around between organisms like trading cards, through a process called horizontal gene transfer. This mechanism is a major factor in processes like antibiotic resistance.

“Rhodopsins are found all over the tree of life and apparently are acquired by organisms obtaining genes from each other over evolutionary time,” said Autumn Peterson, lead author of the study.

The team synthesized a rhodopsin gene from a parasitic fungus, and inserted it into an organelle called the vacuole in the yeast cells. Even without any optimization, the yeast was able to produce energy from light to subsidize its usual energy from oxygen. When lit up, the edited yeast grew about 2% faster than natural yeast, and performed better than edited yeast kept in the dark.

“Here we have a single gene, and we’re just yanking it across contexts into a lineage that’s never been a phototroph before, and it just works,” said Anthony Burnetti, corresponding author of the study. “This says that it really is that easy for this kind of a system, at least sometimes, to do its job in a new organism.”

The team says that the research could help scientists design more productive strains of yeast for everything from beer to biofuels. But their goal in particular was to use it to study evolution, specifically how life may have made the giant leap from single-celled to multi-cellular forms. Last year, the team dabbled in a bit of artificial natural selection and, over thousands of generations, grew yeast to be 20,000 times bigger and 10,000 times tougher, forming clustered colonies that began to show some properties of multicellularism.

One of the main challenges in that project was giving the growing yeast enough energy. Oxygen is its main source, but as the structures grew bigger it was harder to diffuse enough oxygen throughout. The next step in their work is to try to run the multicellular evolution experiment with the phototropic yeast, to see if having more options for energy production gives the microbes a boost.

The research was published in the journal Current Biology.

Source: Georgia Tech

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