May 14, 2009

Microbe makes most of light

Study the light-harvesting components of light-starved bacteria and you've got a model for super-efficient solar cells.

Green sulfur bacteria are the most efficient light-harvesting organisms. They survive by photosynthesizing tiny amounts of light. Their light-absorbing antenna -- chlorosomes -- are much larger than light-harvesting components of other photosynthetic microorganisms and plants.

The combination of nuclear magnetic resonance and cryogenic electron microscopy provided enough information to reveal the green sulfur bacteria's secret: the antenna are made of as many as 250,000 pigment molecules -- bacteriochlorophyll -- that assemble themselves into nested nanotubes. Light-harvesting components of other photosynthetic organisms tend, instead, to be held together with protein molecules.

The chlorophyll molecules pair up head-to-head with tails extending outward. Many thousands of pairs form a spiral pattern to make the nanotubes. The spiral is key to the bacteria's efficiency; the offset pattern allows the molecules to channel and rapidly transmit energy absorbed from photons rather than letting the energy wander from molecule to molecule.

Chlorosomes' simple structure and self-assembly could inspire methods of making highly-efficient and inexpensive solar cells.

Research paper:
Alternating syn-anti bacteriochlorophylls form concentric helical nanotubes in chlorosomes
Proceedings of the National Academy of Sciences, published online May 12, 2009

Researchers' contact:
Huub J. M. de Groot

Related stories and briefs:
Algae proteins boost solar concentrators -- related research
Photosynthesis drives solar fuel cell -- related research

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