When early microbes evolved, some species developed ways to convert sunlight into cellular energy and to use that energy to capture carbon from the atmosphere. The origin of this process, known as photosynthesis, was crucial to the later evolution of plants. The publication today of the analysis of the complete genome sequence of an unusual photosynthetic microbe provides important insights into studies of how that light harvesting mechanism evolved and how it works today.

The bacterium, Chlorobium tepidum, was originally isolated from a hot spring in New Zealand. It is a member of the green-sulfur bacterial group, so known because of the microbes' color and their dependence on sulfur compounds to carry out photosynthesis. Biologists say green-sulfur bacteria are important because they perform photosynthesis in a different way from that of other bacteria and that of plants.

For example, instead of the choloroplasts found in plants, green-sulfur bacteria have organelles called chlorosomes that help generate energy through an electron-transport chain in the microbe's cytoplasmic membrane. Inside the chlorosomes, the chlorophyll and carotenoid molecules that capture light differ from the molecules that other species use to perform photosynthesis. Also, green-sulfur bacteria carry out photosynthesis in the absence of oxygen and do not produce oxygen as a byproduct as plants do.

"Because of their unusual mechanisms of harvesting and using the energy of light, the green-sulfur bacteria are important to understanding the evolution and the mechanisms of both photosynthesis and cellular energy metabolism," said Jonathan A. Eisen, an evolutionary biologist at The Institute for Genomic Research (TIGR) in Rockville, Maryland. "The ability to carry out photosynthesis in the absence of oxygen is particularly important to evolutionary studies since it is believed that the early atmosphere of Earth had little oxygen. That is why some scientists h
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Contact: Jonathan Eisen
jeisen@tigr.org
301-838-3507
The Institute for Genomic Research
1-Jul-2002

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