“Green bacteria” may be used to build artificial photosynthetic systems

May 5th, 2009 - 2:36 pm ICT by ANI  

Washington, May 5 (ANI): An international team of scientists has determined the structure of the chlorophyll molecules in green bacteria that are responsible for harvesting light energy, which one day could be used to build artificial photosynthetic systems.

The scientists found that the chlorophylls are highly efficient at harvesting light energy.

“We found that the orientation of the chlorophyll molecules make green bacteria extremely efficient at harvesting light,” said Donald Bryant, Ernest C. Pollard Professor of Biotechnology at Penn State and one of the team’s leaders.

According to Bryant, green bacteria are a group of organisms that generally live in extremely low-light environments, such as in light-deprived regions of hot springs and at depths of 100 meters in the Black Sea.

The bacteria contain structures called chlorosomes, which contain up to 250,000 chlorophylls.

“The ability to capture light energy and rapidly deliver it to where it needs to go is essential to these bacteria, some of which see only a few photons of light per chlorophyll per day,” said Bryant.

Because they have been so difficult to study, the chlorosomes in green bacteria are the last class of light-harvesting complexes to be characterized structurally by scientists.

Scientists typically characterize molecular structures using X-ray crystallography, a technique that determines the arrangement of atoms in a molecule and ultimately gives information that can be used to create a picture of the molecule.

However, X-ray crystallography could not be used to characterize the chlorosomes in green bacteria because the technique only works for molecules that are uniform in size, shape, and structure.

To get around this problem, the team used a combination of techniques to study the chlorosome.

They used genetic techniques to create a mutant bacterium with a more regular internal structure, cryo-electron microscopy to identify the larger distance constraints for the chlorosome, solid-state nuclear magnetic resonance (NMR) spectroscopy to determine the structure of the chlorosome’s component chlorophyll molecules, and modeling to bring together all of the pieces and create a final picture of the chlorosome.

The last steps for the team were to pull together all of their data and to create a detailed computer model of the structure.

“At first, it seems counterintuitive that green bacteria have managed to evolve a better light-harvesting system by increasing disorder in the chlorosome structure,” said Bryant.

Bryant said that the team’s results may one day be used to build artificial photosynthetic systems that convert solar energy to electricity.

“The interactions that lead to the assembly of the chlorophylls in chlorosomes are rather simple, so they are good models for artificial systems,” he said. (ANI)

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