Chemical engineers in California have found a way to produce useful chemicals in bacteria, using energy from the sun.

With fossil fuels an ever-dwindling resource, engineers must find new ways to meet our energy and chemical production needs. Inspired by plants, a team of researchers at UC Berkeley has found a way of tricking bacteria into photosynthesising. Instead of making food from CO2, water and sunshine, these bacteria are duped into making simple, organic chemicals instead.

Chemist, Kelsey Sakimoto, has been experimenting with a naturally occurring, non-photosynthetic bacteria. As part of its normal respiration, ‘Moorella thermoacetica’ makes acetic acid from carbon dioxide. Acetic acid is a handy molecule that we have plenty of industrial uses for. With a bit of extra engineering, it can be upgraded into fuel, plastics, pharmaceuticals and chemicals for industry.

Four times more efficient than chlorophyll

Working in Peidong Yang’s lab at UC, Berkeley, Sakimoto discovered he could attach tiny solar panels to bacteria. Fed on a mixture of cadmium and amino acids, the bacteria made inorganic, cadmium sulfide nanoparticles. Covering their bodies in the light-collecting semi-conductors, bacteria could harvest the sun’s energy.

“Rather than rely on inefficient chlorophyll to harvest sunlight, I’ve taught bacteria how to grow and cover their bodies with tiny semiconductor nanocrystals,” Sakimoto said. “These nanocrystals are much more efficient than chlorophyll and can be grown at a fraction of the cost of manufactured solar panels.”

The ‘hybrid’ nanoparticles are so efficient they can turn 80% of the sun’s energy into acetic acid. This process is four times more effective than natural, chlorophyll-based photosynthesis. Bacteria will reproduce in the right conditions, making the process zero-waste and self-regenerating.

A more benign light collector is needed

“The thrust of research in my lab is to essentially ‘supercharge’ nanophotosynthetic bacteria by providing them energy in the form of electrons from inorganic semiconductors, like cadmium sulfide, that are efficient light absorbers,” Yang said.

Cadmium sulfide is a bright yellow, inorganic compound used in commercial chemical processes. Historically it was even adopted as a pigment in paint, used by artists such as Monet and Van Gogh. Cadmium compounds are generally thought to be carcinogenic and when inhaled as a dust, cadmium sulfide is toxic. As well as refining the process in the future, the team hope to find more benign light absorbers.

Sakimoto and Yang presented their work at the annual meeting of the American Chemical Society in Washington, DC this August.