The oceanic picoplankton Prochlorococcus - probably the most abundant 
photosynthetic organism on our planet - can grow at great depths where light 
intensity is very low. We have found that the chlorophyll-binding proteins in a 
deep-living strain of this oxyphotobacterium form a ring around a trimer of the 
photosystem I (PS I) photosynthetic reaction centre, a clever arrangement that 
maximizes the capture of light energy in such dim conditions.