Coexistence of phycoerythrin and a chlorophyll a/b antenna in a marine prokaryote.

Prochlorococcus marinus CCMP 1375, a ubiquitous and ecologically important marine prochlorophyte, was bound to possess functional genes coding for the alpha and beta subunits of a phycobiliprotein. The latter is similar to phycoerythrins (PE) from marine Synechococcus cyanobacteria and bind a phycourobilin-like pigment as the major chromophore. However, differences in the sequences of the alpha and beta chains compared with known PE subunits and the presence of a single bilin attachment site on the alpha subunit designate it as a novel PE type, which we propose naming PE-III. P. marinus is the sole prokaryotic organisms known so far that contains chlorophylls a and b as well as phycobilins. These data strongly suggest that the common ancestor of prochlorophytes and the Synechococcus cyanobacteria contained phycobilins. Flow cytometric data from the tropical Pacific Ocean provide evidence that deep populations of Prochlorococcus possess low amounts of a PE-like pigment, which could serve either in light harvesting or nitrogen storage or both.

Earliest evolution associated with closure of the Tropical American Seaway.

Oceanographic changes caused by the emerging Central American isthmus, which completely severed connections between the Caribbean Sea and tropical Pacific Ocean about 3.5 million years ago, began to stimulate evolution of Caribbean reef corals and benthic foraminifera in the Late Miocene. At that time, first appearances of benthic foraminifera increased, especially those species strongly associated with carbonate-rich substrata; reef corals diversified dramatically; and the carbonate content of southern Caribbean deep-sea sediments increased. We suggest that the changes in marine environments caused by the constricting seaway and resulting in increasing carbonate content of sediments induced accelerated origination in reef corals and carbonate-associated benthic foraminifera.