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Research Leads to Improved Fuel Yields from Smaller Antenna Algae

May 13, 2014 - 12:06pm

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Tasios Melis (center) shows plates with tla3 algae and its parent strain to Katie Randolph (left) and Sunita Satyapal during a site visit to his lab at the University of California, Berkeley.

Tasios Melis (center) shows plates with tla3 algae and its parent strain to Katie Randolph (left) and Sunita Satyapal during a site visit to his lab at the University of California, Berkeley.

A study funded by the Energy Department could lead to big improvements in alternative fuel production. Researchers at the University of California, Berkeley have discovered that if particular genes are missing in certain strains of algae, the algae can produce more hydrogen and other fuel from full sunlight than the ordinary algae.

FUNNELING PHOTONS

The single-cell algae Chlamydomonas reinhardtii gets its green color from chlorophyll antennae, the structures that collect light for photosynthesis, the process of converting light energy to chemical energy. Ordinary, dark green C. reinhardtii cells have large chlorophyll antennae that collect more light than the cell actually needs or can even use.

Think of the chlorophyll antenna like funnels that collect the light, in the form of particles called photons, which hit the algae cells. The collected photons are sent to the algae cell’s photosystems, the cellular machines that turn the light energy into chemical energy for different cell activities, including making hydrogen or other biofuels.

Large funnels collect more photons than small ones, which is ideal when light is dim, but under intense light conditions, such as sunlight at noon, they collect many more photons than the photosystems can process at once. When faced with excess photons, the cells can’t keep up and discard the light energy in the form of wasted heat energy. Not only do those cells not use the extra light, they block light from reaching lower layers of cells.

SMALLER ANTENNA, BIGGER EFFICIENCIES  

To address this problem, the Energy Department’s Office of Energy Efficiency and Renewable Energy (EERE) funded groundbreaking research lead by Professor Tasios Melis, who worked to change algae’s genes to make the chlorophyll antennae smaller. Dr. Melis proposed that smaller antennae would mean that, in bright sunlight, cells would only collect a little more light than they can use, and let the rest pass through to the next layer of cells, so that as a group, the algae could use more of the sunlight.  

Professor Melis and his team searched through thousands of mutant algae for ones that were colored a lighter shade of green than their “normal” parent strain, indicating smaller antenna.  The study focused on three such strains, called truncated light-harvesting antenna (tla) mutants, to find out what genes lead to smaller antennae size.

PIECING TOGETHER PROTEINS, IMPROVING PHOTOSYNTHETIC FUEL PRODUCTION  

As detailed in a review article published earlier this year, the Melis lab showed that the tla2 and tla3 strains are each missing a different gene involved in assembling the chlorophyll antennae.

When the cell first makes the protein parts of the antenna, they need to be pieced together to become a working antenna. The process is like assembling a bookshelf - both the pieces of the bookshelf and the tools to put it together are needed.

In both tla2 and tla3 strains a gene for one of the cellular assembly tools is missing, so  the algae cells can still build the antennae but not as well as they could with all the genes present, resulting in  smaller chlorophyll antennae.

As Dr. Melis predicted, the tla2 and tla3 strains’ smaller antennae means that as a group, the cells convert more of the incoming photons into chemical energy, improving light utilization efficiencies to 15% and 25% respectively, compared to 3% in ordinary cells. This means that on an algae farm with full sunlight, the mutant algae strains could make more chemical energy per acre than normal cells.  Since producing chemical energy is the first step needed to make hydrogen or other biofuels, the mutant algae strains could be used to improve the process of creating alternative fuels.

Now that the genes have been identified, researchers can similarly improve other strains of algae and make hydrogen and alternative fuel production even more efficient.

To learn more about how hydrogen energy technology works, visit our Energy Basics site. For more on EERE’s work related to the development and deployment of hydrogen, visit our Fuel Cells Technologies site

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