Bacterium trained to perform artificial photosynthesis

Scientists have successfully trained bacteria to perform photosynthesis - despite being non-photosynthetic, an advance that could lead to the next generation of solar-to-chemical conversion technologies.
They used the bacterium Moorella thermoacetica to synthesise semiconductor nanoparticles in a hybrid artificial photosynthesis system for converting sunlight into valuable chemical products.
"We've demonstrated the first self-photosensitisation of a non-photosynthetic bacterium, M thermoacetica, with cadmium sulfide nanoparticles to produce acetic acid from carbon dioxide at efficiencies and yield that are comparable to or may even exceed the capabilities of natural photosynthesis," said Peidong Yang, from the University of California's Lawrence Berkeley National Laboratory.
"The bacteria/inorganic-semiconductor hybrid artificial photosynthesis system we've created is self-replicating through the bio-precipitation of cadmium sulphide nanoparticles, which serve as the light harvester to sustain cellular metabolism," Yang said.

"Demonstrating this cyborgian ability to self-augment the functionality of biological systems through inorganic chemistry opens up the integration of biotic and abiotic components for the next generation of advanced solar-to-chemical conversion technologies," he said.
Photosynthesis is the process by which nature harvests sunlight and uses the solar energy to synthesise carbohydrates from carbon dioxide and water.

Artificial versions of photosynthesis are being explored for the clean, green and sustainable production of fuels and plastics made from petroleum.
Researchers have been at the forefront of developing artificial photosynthetic technologies that can realise the full potential of solar-to-chemical synthesis.
"By inducing the self-photosensitisation of M thermoacetica with cadmium sulfide nanoparticles, we enabled the photosynthesis of acetic acid from carbon dioxide over several days of light-dark cycles at relatively high quantum yields, demonstrating a self-replicating route toward solar-to-chemical carbon dioxide reduction," Yang said.

Cadmium sulfide is a well-studied semiconductor with a band structure and that is well-suited for photosynthesis.
As both an "electrograph" (meaning it can undergo direct electron transfers from an electrode), and an "acetogen" (meaning it can direct nearly 90 per cent of its photosynthetic products towards acetic acid), M thermoacetica serves as the ideal model organism for demonstrating the capabilities of this hybrid artificial photosynthesis system.
"Our hybrid system combines the best of both worlds - the light-harvesting capabilities of semiconductors with the catalytic power of biology," Yang said.
"In this study, we've demonstrated not only that biomaterials can be of sufficient quality to carry out useful photochemistry, but that in some ways they may be even more advantageous in biological applications," he said.

The study was published in the journal Science.