The structure of the exciton manifold in the core bacteriochlorophyll antenna complexes from the purple photosynthetic bacterium Rhodobacter sphaeroides has been studied at 5 K using conventional and polarized fluorescence excitation spectroscopy supported with model simulations. Exciton bandwidths in the range of 2100-2200 cm(-1), depending on sample integrity, have been determined in correlation with the largest mean coupling energy between the nearest-neighbor bacteriochlorophyll molecules close to 600 cm-1. These numbers are considerably bigger than those in any other native antenna complex known. Another noteworthy feature of these complexes is dominance of structural (off-diagonal) static disorder over the energetic (diagonal) disorder. (c) 2005 Elsevier B.V. All rights reserved.