Yeast gets a solar-powered boost

The simple brewer’s yeast Saccharomyces cerevisiae is one of the most well-characterized microorganisms on the planet. It is used to ferment alcohol, as well as synthesize drugs and feedstock chemicals. Now, researchers have created yeast that can perform another trick: harnessing sunlight.

Neel Joshi’s group at Harvard University added semiconductor nanoparticles to the surface of genetically engineered yeast to generate an inorganic, biological, hybrid organism. The yeast grabs electrons, which are produced when light shines on the particles, to drive production of shikimic acid—used to make oseltamivir, sold under the brand name Tamiflu.

Joshi tells C&EN that the project was conceived of by two postdocs, Junling Guo and Miguel Suástegui, who have backgrounds in materials science and metabolic engineering, respectively. “They came up with this idea,” Joshi explains, “which initially I didn’t think was going to work.” But he was proved wrong. “It worked beautifully.”

The researchers fixed indium phosphide nanoparticles onto the yeast’s cell wall using simple polyphenol chemistry (Science 2018, DOI:10.1126/science.aat9777). When white light shines on the solar-powered cells, they take up the photogenerated electrons and funnel them into regenerating the compound NADPH, a cofactor broken down during shikimic acid synthesis, so it can participate again.

“What they’ve actually done is fairly impressive, but I think it’s the concept that is the most powerful here,” says Alison Narayan, who works on biosynthesis at the University of Michigan. She says the work interests her for bringing photocatalysis into yeast, as well as broadly addressing cofactor regeneration—a process that typically requires resources like sugars.

The system won’t be used to produce shikimic acid industrially anytime soon. Joshi admits that the yields of the hybrid brewing process are not high enough, and other parts of the system need to be optimized. But he adds that because NADPH appears in many biosynthetic pathways, his lab’s hybrid approach could be used to make other target molecules, simply by choosing different genetically modified yeasts.