08 September 2000
Vol 289, Issue 5485

About The Cover

Cover image expansion

COVER Chloroflexus aurantiacus, a green nonsulfur bacterium (orange), growing on an agar layer with the cyanobacterium Synechococcus sp. (green). Anoxygenic photosynthetic bacteria, such as Chloroflexus, which do not produce oxygen during the process of photosynthesis, evolved millions of years before oxygenic photosynthetic bacteria, such as Synechococcus, which generate oxygen as a by-product of the photochemical reaction. See page 1724. [Photo: R. Castenholz]