DAVIS, Calif., Feb. 21 U.S. scientists have sequenced the genome of a giant clam that lives deep in the ocean and depends on symbiotic bacteria as sunlight.Near the ocean's surface, sunlight allows green plants to use carbon from the air to build their bodies. But around hydrothermal vents deep in the ocean the giant clams with no gut and no functional digestive system depend on symbiotic bacteria to use energy from hydrogen sulfide to replace sunlight.
The difference here is that while plants get their energy and carbon via photosynthesis by chloroplast symbionts, this clam gets its energy via chemosynthesis, said University of California-Davis Professor Jonathan Eisen, He noted photosynthesis in green plants is accomplished by chloroplasts, descended from primitive single-celled organisms incorporated into other cells billions of years ago.
The energy from hydrogen sulfide is used to drive carbon fixation in much the same way that chloroplasts carry out carbon fixation, Eisen said. The symbiotic bacteria also fix nitrogen and produce amino acids, vitamins and other nutrients required by the clam. Studies of the deep sea have implications for studying the origins of life on Earth, Eisen said.
Copyright 2007 by UPI
