Bacteria used to convert solar energy into liquid fuel

Harvard scientists have created a system that uses bacteria to convert solar energy into a liquid fuel.
The work integrates an "artificial leaf," which uses a catalyst to make sunlight split water into hydrogen and oxygen, with a bacterium engineered to convert carbon dioxide plus hydrogen into the liquid fuel isopropanol.
"This is a proof of concept that you can have a way of harvesting solar energy and storing it in the form of a liquid fuel," said Pamela Silver, Professor of Biochemistry and Systems Biology at Harvard Medical School (HMS).
"It's not like we're trying to make some super-convoluted system. Instead, we are looking for simplicity and ease of use," Silver said.

The artificial leaf invented by the paper's senior author, Daniel Nocera, Professor of Energy at Harvard University, depends on catalysts made from materials that are inexpensive and readily accessible.
"The catalysts I made are extremely well adapted and compatible with the growth conditions you need for living organisms like a bacterium," Nocera said.

In their new system, once the artificial leaf produces oxygen and hydrogen, the hydrogen is fed to a bacterium called Ralstonia eutropha.
An enzyme takes the hydrogen back to protons and electrons, then combines them with carbon dioxide to replicate - making more cells.
Next, based on discoveries made earlier by Anthony Sinskey, professor of microbiology and of health sciences and technology at The Massachusetts Institute of Technology (MIT), new pathways in the bacterium are metabolically engineered to make isopropanol.

The same principles could be employed to produce drugs such as vitamins in small amounts, Silver said.
The team's immediate challenge is to increase the bionic leaf's ability to translate solar energy to biomass by optimising the catalyst and the bacteria.
Their goal is 5 per cent efficiency, compared to nature's rate of 1 per cent efficiency for photosynthesis to turn sunlight into biomass.
The findings are published in the journal PNAS.