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Photosynth Res (2010) 104:245255 DOI 10.1007/s11120-010-9533-0
REVIEW
The chlorosome: a prototype for efcient light harvesting in photosynthesis
Gert T. Oostergetel Herbert van Amerongen
Egbert J. Boekema
Received: 24 November 2009 / Accepted: 16 January 2010 / Published online: 4 February 2010 The Author(s) 2010. This article is published with open access at Springerlink.com
Abstract Three phyla of bacteria include phototrophs that contain unique antenna systems, chlorosomes, as the principal light-harvesting apparatus. Chlorosomes are the largest known supramolecular antenna systems and contain hundreds of thousands of BChl c/d/e molecules enclosed by a single membrane leaet and a baseplate. The BChl pigments are organized via self-assembly and do not require proteins to provide a scaffold for efcient light harvesting. Their excitation energy ows via a small protein, CsmA embedded in the baseplate to the photosynthetic reaction centres. Chlorosomes allow for photosynthesis at very low light intensities by ultra-rapid transfer of excitations to reaction centres and enable organisms with chlorosomes to live at extraordinarily low light intensities under which no other phototrophic organisms can grow. This article reviews several aspects of chlorosomes: the supramolecular and molecular organizations and the light-harvesting and spectroscopic properties. In addition, it provides some novel information about the organization of the baseplate.
Keywords Chlorosome Photosynthesis
Electron microscopy Spectroscopy
Introduction
Since the earliest photosynthetic organisms developed reaction centres, additional peripheral antenna systems have evolved for light harvesting. In these light-harvesting systems, dozens, hundreds or even thousands of (bacterio)chlorophylls can funnel their excitation energy towards reaction centres for charge separation. The green photo-synthetic bacteria are anoxygenic phototrophs that contain unique antenna complexes, known as chlorosomes (Blankenship and Matsuura 2003). A chlorosome is actually a kind of organelle. In addition to the green sulphur bacteria (phylum Chlorobi), they are also present in some lamentous anoxygenic phototrophs of the phylum Chloroexi (formerly know as green non-sulphur bacteria), and in the newly discovered aerobic phototroph, Candidatus Chloracidobacterium thermophilum (Cab. thermophilum) of the phylum Acidobacteria (Bryant et al. 2007). The green sulphur bacteria form the best studied group, and especially Chlorobaculum tepidum (also known as Chlorobium) from the family of Chlorobiaceae, has emerged as a model organism for the group. Within these organisms, the ow of excitation energy goes in the following direction:
Pigments within chlorosomes
! CsmA protein in...