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Release: Nov. 19, 2002

Biological sciences professor dates origin of photosynthetic algae at 1.2 billion years ago

A University of Iowa researcher has revised scientists' estimate of the date of origin of photosynthetic algae -- responsible for about one-half of Earth's oxygen -- from some 500 million years ago to 1.2 billion years ago.

Debashish Bhattacharya, assistant professor of biological sciences in the University of Iowa College of Liberal Arts and Sciences, whose work is featured on the cover and inside the Nov. 18 issue of the journal Proceedings of the National Academy of Sciences (PNAS), and his colleagues used genetic analysis to trace the origin of certain algae to a common ancestor. He says their paper is "something of a landmark" because it is one of the first of its kind to arrive at such an early date for the beginning of photosynthesis in many different kinds of marine and freshwater algae.

"This paper provides proof for the single origin of a vast assemblage of photosynthetic algae such as diatoms and giant kelps that all contain the light-harvesting pigment chlorophyll c," he says. "It dates their origin at about 1.2 billion years ago, much earlier than previously thought. This changes our views on when the Earth was first dominated by photosynthetic eukaryotes, or single-celled organisms."

Bhattacharya notes that algae, as primary producers in the food chain, are critical to maintaining life on Earth. In particular, algae containing chlorophyll c dominate the world's oceans, he says. His research interests involve studying the origin of plastids, the cell organelles responsible for algal photosynthesis, and how endosymbiosis -- the process of one cell engulfing another -- has driven the origin and diversification of photosynthetic eukaryotes.

"In this paper, we found that a single secondary endosymbiosis, in which a unicellular protist (one-celled organism) engulfed a red alga, occurred about 1.2 billion years ago, giving birth to all chlorophyll c-containing algae. Generally, our findings suggest that endosymbiosis is a significant machine for generating biodiversity on our planet and that many non-photosynthetic species alive today, such as water molds, may in fact have had a photosynthetic ancestor, and these taxa have lost their plastids over one billion years of evolutionary time," he says.

Co-authors of the paper, "Single ancient origin of chromist plastid," are Bhattacharya, Hwan Su Yoon, Jeremiah D. Hackett, of the UI department of biological sciences and Center for Comparative Genomics, and Gabriele Pinto, Dipartimento di Biologia vegetale, Università "Federico II," Napoli, Italy.

Bhattacharya directs one of the best-equipped laboratories of its kind for investigating the evolutionary history of algae. His group recently received a $790,000 grant from the National Science Foundation and the U.S. Department of Agriculture to generate genomic databases for the toxic dinoflagelate Alexandrium tamarense and for the open-ocean, bloom-forming Emiliania huxleyi, a resource of value to many scientists working on the evolution and basic biology of various algae.