September 12, 2000

1 min read

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Photosynthesis's Purple Roots

By Kate Wong

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As the fundamental chemical process that sustains life on Earth, photosynthesis has long been the subject of intense scientific investigation. Researchers have known for years that the process originated in bacteria, yet details of its origin and evolution remained elusive. Now new molecular research reported in the journal Science is shedding light on the story and pushing back the origin of this pivotal innovation.

By sequencing photosynthesis genes in two types of green bacteria and comparing those with data from the other lineages of photosynthetic bacteria, the scientists generated a photosynthesis phylogeny, or family tree. The results revealed that those bacteria containing photosystems in which oxygen is not produced, such as purple bacteria, evolved first. Bacteria containing oxygen-producing photosystems evolved later, in cyanobacteria, which eventually gave rise to the chloroplasts found in today's green plants.

The molecular data contradict the conventional scenario for the emergence of this energy-harnessing mechanism. Purple bacteria were thought to have been one of the last bacterial groups to evolve, because bacteriochlorophyll--the bacterial version of the light-capturing molecule--is more complex than the chlorophyll used by green plants. The new data, however, suggest that chlorophyll derived from bacteriochlorophyll, not the other way around.

Kate Wong is an award-winning science writer and senior editor for features at Scientific American, where she has focused on evolution, ecology, anthropology, archaeology, paleontology and animal behavior. She is fascinated by human origins, which she has covered for nearly 30 years. Recently she has become obsessed with birds. Her reporting has taken her to caves in France and Croatia that Neandertals once called home to the shores of Kenya’s Lake Turkana in search of the oldest stone tools in the world, as well as to Madagascar on an expedition to unearth ancient mammals and dinosaurs, the icy waters of Antarctica, where humpback whales feast on krill, and a “Big Day” race around the state of Connecticut to find as many bird species as possible in 24 hours. Wong is co-author, with Donald Johanson, of Lucy’s Legacy: The Quest for Human Origins. She holds a bachelor of science degree in biological anthropology and zoology from the University of Michigan. Follow her on Bluesky @katewong.bsky.social

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