Solar-powered cyborg bacteria turn sunlight into useful chemicals


By coating bacteria in cadmium sulfide crystals, researchers have made them into highly efficient bioreactors for producing acetic acid. Andrew Masterson reports.


Diagram showing bioreactor (left) loaded with bacteria decorated with cadmium sulfide, light-absorbing nanocrystals (middle) to convert light, water and carbon dioxide into useful chemicals (right).
Diagram showing bioreactor (left) loaded with bacteria decorated with cadmium sulfide, light-absorbing nanocrystals (middle) to convert light, water and carbon dioxide into useful chemicals (right).
Kelsey K. Sakimoto

The development of photosynthesis in primitive cyanobacteria is recognised as one of the pivotal developments in the evolution of complex life on Earth.

However, photosynthesis itself – the conversion of sunlight into sugar – is a relatively inefficient process.

Around the world, scientists are striving to find ways to improve it – either artificially, or through bioengineering.

Now, researchers from the University of California, Berkeley (UCB), have uncovered a method that combines both approaches. Effectively, they have induced bacteria to coat themselves in tiny, highly efficient solar panels.

Lead researcher Kelsey Sakimoto worked with common bacteria known as Moorella thermoacetica. The species does not naturally photosynthesise, but Sakimoto and his colleagues induced a population of the microbes to cover themselves in semiconductor nanocrystals.

The work is an extension of research carried out by Peidong Yang, also at UCB, who specialises in creating inorganic semi-conductors and binding them to bacteria, producing useful chemicals from the interaction of carbon dioxide and water.

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

Sakimoto chose M. thermoacetica as a research target because it produces acetic acid as a function of its normal respiratory cycle. The acid is currently the focus of widespread experimentation because of its usefulness in the creation of polymers and other commercial useful products, often achieved by the application of other bacterial species.

The researchers successfully induced the bacteria to bond with a combination of cadmium and the amino acid cysteine. Cysteine contains a sulfur atom, causing the bacteria to synthesise cadmium sulfide (CdS) nanoparticles – which function as solar panels.

The resulting hybrids – dubbed M. thermoacetica-CdS – produced acetic acid using carbon dioxide, water and light at a stunning 80% efficiency.

“Rather than rely on inefficient chlorophyll to harvest sunlight, I’ve taught bacteria how to grow and cover their bodies with tiny semiconductor nanocrystals,” says Sakimoto.

“These nanocrystals are much more efficient than chlorophyll and can be grown at a fraction of the cost of manufactured solar panels.”

The research was presented at the 254th National Meeting & Exposition of the American Chemical Society, held in Washington DC, US.

  1. http://ma.ecsdl.org/content/MA2017-01/35/1677.short
  2. http://onlinelibrary.wiley.com/doi/10.1111/nph.14307/full
  3. http://www.sciencedirect.com/science/article/pii/S0043135417304323
  4. https://www.acs.org/content/acs/en/meetings/fall-2017.html
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