Cell-Free Artificial Photosynthesis with Frog Foam

We owe a lot to frogs and toads. They help us welcome in spring and summer with their peeps, croaks and snores in the evenings. They serve as bioindicator species that alert us to damaged or toxic environments. And, now, they may even help us kick the fossil fuel habit.

Biofuels, based on harvesting and converting plant biomass to fuel have been touted as an alternative to nonrenewable fossil fuels. The argument for them goes something like this:  Nature has a means for converting sunlight energy to chemical energy (photosynthesis). Why not just let Nature do the work for us, and harness that power?

The problem with biofuels such as those derived from corn, or even prairie grasses, is that extracting the captured energy is incredibly inefficient. First off, the plants use a lot of that captured sunlight energy for their own metabolism. Second, precious natural resources such as arable land and water must be used to produce the biomass, and the process of extracting the stored energy requires energy itself. All of this results in efficiency rates as low as five percent.

But what if we could create highly efficient artificial photosynthetic systems? Such in vitro carbon fixation experiments have been done. Using the suite of enzymes involved in photosynthesis, carbon sequestration, and carbohydrate generation along with a reconstituted ATP synthase and bacteriorhodopsin, in vitro carbon fixation has been achieved. The sticking point is efficiency.

Wendell and colleagues report an improvement on these in vitro systems using surfactant isolated from the biofoam nests of the Tungara frog. The Ranaspumin-2 (literally “frog spit”) surfactant protein formed a foam that allowed lipid vesicles and coupled enzyme activity to concentrate in tiny micro channels. Even though the foam was able to concentrate the enzyme activities so tightly, it still allowed light and air to enter the system. The high local concentration of enzyme activity resulted in chemical conversion efficiencies of nearly 96%.

Besides efficiency, the system has other advantages too. It doesn’t require acres and acres of arable land, so food production isn’t disrupted. Additionally, it will work in areas of high carbon dioxide concentration, like the exhaust of coal-burning power plants. Think about it: this system could reduce pollution and produce renewable energy simultaneously. Additionally, this system could be used in unusual places like roof tops in large cities—anywhere there is light and air but not much else available.

So frog spit may hold the key to creating a solar energy capture system that is efficient, renewable and nonpolluting. I’ll think about that the next time I’m strolling along on a summer’s eve and the frogs are calling.

Wendell, D., Todd, J., & Montemagno, C. (2010). Artificial Photosynthesis in Ranaspumin-2 Based Foam Nano Letters DOI: 10.1021/nl100550k