The green plants that cover the land and fill the seas form the main basis for much of life on Earth. Yet the tiny piece of cellular machinery that makes all of this possible, chlorophyll, is surprisingly inefficient. In a bid to replicate photosynthesis, and as such improve upon it, researchers have managed to create “cyborg” bacteria, covered in tiny semiconductors that take sunlight, carbon dioxide, and water, and turn it into a potential fuel.
“Rather than rely on inefficient chlorophyll to harvest sunlight, I've taught bacteria how to grow and cover their bodies with tiny semiconductor nanocrystals,” explained Kelsey K Sakimoto, who carried out the research that was presented at the American Chemical Society meeting this week. “These nanocrystals are much more efficient than chlorophyll and can be grown at a fraction of the cost of manufactured solar panels.”
Amazingly, it didn’t actually take that much tweaking to make the bacteria coat themselves in the semiconductors. After trawling through old microbiology literature, the researchers found that some bacteria will naturally produce heavy metal crystals on their surface if they are exposed to cadmium, mercury, or lead, as a form of natural defense.
The researchers simply realized that these heavy metal sulfides are in effect tiny solar panels that line the surface of the bacteria. “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,” explained Peidong Yang, who runs the lab in which the research is being carried out.
The souped up bacteria use the energy from the semiconductors to take carbon dioxide and water – the same two building blocks for photosynthesis – and churn out acetic acid, which is effectively vinegar. The efficiency of this process has been measured at a whopping 80 percent, far higher than anything we can achieve with solar panels, and roughly six times more efficient than plants manage it themselves.
But it is what we then do with this acetic acid that is important. Other researchers have been working on way to engineer the humble E. coli to take up acetic acid, and then turn it into the fuel butanol or a polymer known as polyhydroxybutyrate. If both the semiconductor bacteria, and the fuel producing E. coli can be scaled up, then it could be a new way to synthesize biofuel using just sunlight, water, and carbon dioxide.
The researchers hope to refine their ideas, as currently, it is still more attractive to simply use algae in massive vats than to grow a broth of cyborg bacteria. But they are confident that in the future, there may well be a place for their findings.