Biologists Harness Light-Powered Yeast for Evolution, Biofuels, and Cellular Aging Insights

The green rhodopsin proteins found within the blue cell walls of yeast assist their growth when they are subjected to light exposure, according to Anthony Burnetti from the Georgia Institute of Technology.

Yeast, commonly known for its ability to ferment carbohydrates for products like bread and beer, typically thrives in dark settings. Light exposure can interfere with and potentially ruin the fermentation procedure.

In a revolutionary step, a study recently published in Current Biology by researchers from Georgia Tech's School of Biological Sciences, reveal that they have bioengineered one of the first yeast strains that seemingly prefers light.

To everyone's surprise, converting the yeast into phototrophs, or organisms that harness light energy, was unexpectedly simple, according to Anthony Burnetti, a research scientist in William Ratcliff’s lab and the study's corresponding author. He reveals that they only needed to manipulate a single gene, resulting in the yeast growing 2% faster in light than in the dark.

This effortless inclusion of such a trait could have significant implications for our grasp of how the trait originated and how it can be utilized to examine things such as biofuel production, evolution, and cell aging.

The investigation was motivated by the team’s previous research into the evolution of multicellular life, where they discovered that the lack of energy proved to be a significant obstacle for multicellular evolution.

One solution to enhance an organism's energy without using oxygen is by exposing it to light. However, the evolutionary process of harnessing light into usable energy can be complex. For instance, plants, which use light for energy, need a variety of genes and proteins that are challenging to create and transfer to other organisms.

Thankfully, plants aren't the sole organisms capable of transforming light into energy. Rhodopsins, proteins that can convert light to energy without the need for additional cellular machinery, provide a simpler alternative for organisms.

Autumn Peterson, a Biology Ph.D. student working with Ratcliff and lead author of the study, explains that rhodopsins are found ubiquitously in the tree of life and are acquired by organisms through sharing genes over the course of evolution.

This process of sharing is known as horizontal gene transfer, allowing organisms to engage in speedy evolutionary leaps. One typical example is how bacteria swiftly develop immunity to certain antibiotics. This transfer can occur with various forms of genetic data and is particularly prevalent with rhodopsin proteins.

Burnetti elaborates that while exploring methods to introduce rhodopsins into multicelled yeast, they discovered that they could gain insights about the horizontal transfer of rhodopsins in evolution's past by introducing them into regular, single-celled yeast.

To test if they could equip a single-celled organism with sun-powered rhodopsin, the team added a rhodopsin gene from a parasitic fungus to common baker’s yeast. This gene codes for a rhodopsin form that can be inserted into the cell’s vacuole, which, like mitochondria, can transform chemical gradients made by proteins such as rhodopsin into energy.

Upon receiving this vacuolar rhodopsin, the yeast's growth improved by approximately 2% when exposed to light, providing a significant evolutionary advantage.

“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,” says Burnetti. “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.”

This simplicity provides key evolutionary insights and says a lot about “the ease with which rhodopsins have been able to spread across so many lineages and why that may be so,” explains Peterson, who Peterson recently received a Howard Hughes Medical Institute (HHMI) Gilliam Fellowship for her work. Carina Baskett, grant writer for Georgia Tech’s Center for Microbial Dynamics and Infection, also worked on the study.

Because vacuolar function may contribute to cellular aging, the group has also initiated collaborations to study how rhodopsins may be able to reduce aging effects in the yeast. Other researchers are already starting to use similar new, solar-powered yeast to study advancing bioproduction, which could mark big improvements for things like synthesizing biofuels.

Ratcliff and his group, however, are mostly keen to explore how this added benefit could impact the single-celled yeast’s journey to a multicellular organism.

“We have this beautiful model system of simple multicellularity,” says Burnetti, referring to the long-running Multicellularity Long-Term Evolution Experiment (MuLTEE). “We want to give it phototrophy and see how it changes its evolution.”