Marine phytoplanktons represent approximately 1% of the Earth's photosynthetic biomass but account for nearly 50% of the net primary productivity of the biosphere. These organisms occupy the euphotic zone of the ocean—the upper, illuminated zone of aquatic ecosystems where photosynthesis is possible. High light adapted species, such as Synechococcus species, occupy the nutrient-poor, light-rich upper 25 m of the zone where white/blue-green light is available. Low light adapted species are found further down the euphotic zone where blue-violet penetrates and where the environment is nutrient rich. The high light adapted Synechococcus use phycobilisomes for light harvesting, while Prochlorococcus maintain the functionally analogous chlorophyll a2/b2 Pcbs proteins. Papers concurrently published in Nature and PNAS report analysis of the genomes of Prochlorococcus SS120, MED4, MIT9313, and Synechococcus WH8102.

In the August 11 PNAS, Alexis Dufresne and colleagues at the Centre National de la Recherche Scientifique and Université Paris sequenced the...

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