Researchers
use bacteria to convert solar energy into liquid fuel
Harvard Medical School, Science
Daily
Harvesting sunlight is a trick plants mastered more than a
billion years ago, using solar energy to feed themselves from the air and water
around them in the process we know as photosynthesis.
Scientists have also figured out how to harness solar energy,
using electricity from photovoltaic cells to yield hydrogen that can be later
used in fuel cells. But hydrogen has failed to catch on as a practical fuel for
cars or for power generation in a world designed around liquid fuels.
Now scientists from a team spanning Harvard University's Faculty
of Arts and Sciences, Harvard Medical School and the Wyss Institute for
Biologically Inspired Engineering at Harvard University have created a system
that uses bacteria to convert solar energy into a liquid fuel.
Their 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.
Pamela Silver, the Elliott T. and Onie H. Adams Professor of
Biochemistry and Systems Biology at HMS and an author of the paper, calls the
system a bionic leaf, a nod to the artificial leaf invented by the paper's
senior author, Daniel Nocera, the Patterson Rockwood Professor of Energy at
Harvard University.
"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
Silver, who is Core Faculty at the Wyss Institute. "Dan's formidable
discovery of the catalyst really set this off, and we had a mission of wanting
to interface some kinds of organisms with the harvesting of solar energy. It
was a perfect match."
Silver and Nocera began collaborating two years ago, shortly
after Nocera came to Harvard from MIT. They shared an interest in
"personalized energy," or the concept of making energy locally, as
opposed to the current system, which in the example of oil means production is
centralized and then sent to gas stations. Local energy would be attractive in
the developing world.
"It's not like we're trying to make some super-convoluted
system," Silver said. "Instead, we are looking for simplicity and
ease of use."
In a similar vein, Nocera's artificial leaf 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 MIT, new
pathways in the bacterium are metabolically engineered to make isopropanol.
"The advantage of interfacing the inorganic catalyst with
biology is you have an unprecedented platform for chemical synthesis that you
don't have with inorganic catalysts alone," said Brendan Colón, a graduate
student in systems biology in the Silver lab and a co-author of the paper.
"Solar-to-chemical production is the heart of this paper, and so far we've
been using plants for that, but we are using the unprecedented ability of
biology to make lots of compounds."
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 optimizing the catalyst and the
bacteria. Their goal is 5 percent efficiency, compared to nature's rate of 1
percent efficiency for photosynthesis to turn sunlight into biomass.
"We're almost at a 1 percent efficiency rate of converting
sunlight into isopropanol," Nocera said. "There have been 2.6 billion
years of evolution, and Pam and I working together a year and a half have
already achieved the efficiency of photosynthesis."
Story
Source:
The above story is based on materials provided
by Harvard Medical School.
The original article was written by Elizabeth Cooney. Note: Materials may be edited for
content and length.
Journal
Reference:
Joseph P. Torella, Christopher J. Gagliardi, Janice S. Chen, D.
Kwabena Bediako, Brendan Colón, Jeffery C. Way, Pamela A. Silver, Daniel G.
Nocera. Efficient
solar-to-fuels production from a hybrid microbial–water-splitting catalyst
system. Proceedings
of the National Academy of Sciences, 2015; 201424872 DOI:10.1073/pnas.1424872112
Cite
This Page:
Harvard Medical School. "Bionic leaf: Researchers use
bacteria to convert solar energy into liquid fuel." Science Daily,
9 February 2015.
<www.sciencedaily.com/releases/2015/02/150209161423.htm>.
