Solar Cells for Bacteria?

by Emil Morhardt

Non-photosynthetic bacteria (most of them) are capable of all sorts of chemical syntheses, especially when bioengineered. But they all require an energy source. What if that source could be light? The obvious thing to do is to implant them with photosynthetic pathways, but this wa-a-ay beyond current bioengineering capabilities, so maybe it would be possible just to hand them energy from miniature solar cells swimming around in the same solution they are living in. This seemingly highly improbable situation has just been accomplished by Kelsey Sakimoto and co-workers at Berkeley to facilitate the production of acetic acid from carbon dioxide by the non-photosynthetic bacteria, Moorella thermoacetica. This uses up the greenhouse gas CO2 while producing a basic chemical that can be “upgraded to high-value products by wild-type and genetically engineered organisms.”

The system works by the bacteria precipitating cadmium sulfide nanoparticles out of the solution in which they reside, When light strikes these nano-particles they carry out photosynthesis, absorbing a photon to produce an electron and hole pair. The electron is then used to synthesize acetic acid from the CO2 in solution. The authors think that this system has the potential to exceed the utility of natural photosynthesis. An additional advantage is that unlike natural photosynthesis which results in biological molecules such as sugars and cellulose which then need further processing to be useful for other purposes, this system just produces acetic acid which is of no utility to the bsctreria, so it remains available for collection in the solution without further processing.

Sakimoto, K.K., Wong, A.B., Yang, P., 2016. Self-photosensitization of nonphotosynthetic bacteria for solar-to-chemical production. Science 351, 74-77.