Using light for energy: examining the evolution of phototrophic metabolism through synthetic construction

Abstract

Evolutionary innovations helped transform life on Earth. The origin of phototrophy was pivotal to increasing biomass, by utilizing light-driven energy transport to drive biological processes. Retinalophototrophy constitutes one of two phototrophic pathways on Earth, consisting of a simple system of microbial rhodopsins which are exemplars of horizontal gene transfer. Here, we seek to determine if Saccharomyces cerevisiae, a heterotrophic fungus, can function as a facultative artificial phototroph after acquiring only one rhodopsin gene. We investigate the fitness effects of turning yeast phototrophic by using synthetic biology to insert U. maydis rhodopsin into the vacuole of budding yeast. We observed a selective advantage in unicellular yeast with faster growth of yeast bearing rhodopsin in the presence of green light. This simple model illustrates the capacity of horizontal gene transfer to have a large phenotypic effect, with one gene enabling the transfer of phototrophic energy production into a modern eukaryote. While subject to the constraints of any given organism, this illustrates how single horizontal gene transfer events may be used to alter ecological niches and circumvent fitness constraints.

Engineering yeast with a light-driven proton pump system in the vacuolar membrane

“…In previous studies, increases in intracellular ATP supply were achieved by expressing dR in the mitochondria of eukaryotic cells, such as mammalian cells [ 8 ] and Drosophila [ 9 ]. A trial of the expression of rhodopsin in the vacuoles of S. cerevisiae was preliminarily reported in a patent in 2021 [ 17 ] and a preprint in 2023 [ 18 ]; however, the effect of this expression in vacuoles and cellular energetic metabolism has not been reported previously. This study is the first report describing the direct measurement of light-driven proton pumping activity from isolated vacuoles expressing bacterial rhodopsin (Fig.…”

Design and Construction of Artificial Biological Systems for One-Carbon Utilization

“…Most recently, Burnetti and Ratcliff collaboratively engineered S. cerevisiae into a facultative phototroph by introducing a rhodopsin protein from Ustilago maydis into the vacuole, enabling light-driven proton pumping into the vacuolar compartment without consuming ATP. The findings demonstrated that the yeast engineered with rhodopsins exhibit a selective growth advantage under green light, displaying faster growth rates than their nonphototrophic ancestor and rhodopsin-expressing yeast grown in the dark [ 82 ]. To convert CO 2 into value-added compounds continuously, Erb and coworkers [ 83 ] created a modular platform for continuously converting CO 2 to acetyl- and malonyl-CoA that were converted into monoterpenes, sesquiterpenes, and polyketides via the use of varied terpene and polyketide synthases.…”