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Journal of Bacteriology, November 2009, p. 6701-6708, Vol. 191, No. 21
0021-9193/09/$08.00+0     doi:10.1128/JB.00690-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Structure of Chlorosomes from the Green Filamentous Bacterium Chloroflexus aurantiacus{triangledown} ,{dagger}

Jakub Psencík,1 Aaron M. Collins,2 Lassi Liljeroos,3 Mika Torkkeli,4 Pasi Laurinmäki,3 Hermanus M. Ansink,3,{ddagger} Teemu P. Ikonen,4,§ Ritva E. Serimaa,4 Robert E. Blankenship,2 Roman Tuma,3,5 and Sarah J. Butcher3*

Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic,1 Department of Chemistry, Washington University, St. Louis, Missouri,2 Institute of Biotechnology and Department of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland,3 Department of Physical Sciences, University of Helsinki, Helsinki, Finland,4 The Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom5

Received 27 May 2009/ Accepted 18 August 2009

The green filamentous bacterium Chloroflexus aurantiacus employs chlorosomes as photosynthetic antennae. Chlorosomes contain bacteriochlorophyll aggregates and are attached to the inner side of a plasma membrane via a protein baseplate. The structure of chlorosomes from C. aurantiacus was investigated by using a combination of cryo-electron microscopy and X-ray diffraction and compared with that of Chlorobi species. Cryo-electron tomography revealed thin chlorosomes for which a distinct crystalline baseplate lattice was visualized in high-resolution projections. The baseplate is present only on one side of the chlorosome, and the lattice dimensions suggest that a dimer of the CsmA protein is the building block. The bacteriochlorophyll aggregates inside the chlorosome are arranged in lamellae, but the spacing is much greater than that in Chlorobi species. A comparison of chlorosomes from different species suggested that the lamellar spacing is proportional to the chain length of the esterifying alcohols. C. aurantiacus chlorosomes accumulate larger quantities of carotenoids under high-light conditions, presumably to provide photoprotection. The wider lamellae allow accommodation of the additional carotenoids and lead to increased disorder within the lamellae.

* Corresponding author. Mailing address: Institute of Biotechnology and Department of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland. Phone: 358 919159563. Fax: 358 919159930. E-mail: sarah.butcher{at}helsinki.fi

{triangledown} Published ahead of print on 28 August 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Free University of Amsterdam Medical Centre, Amsterdam, The Netherlands.

§ Present address: EMBL Hamburg, c/o DESY, Notkestraße 85, 22603 Hamburg, Germany.

Journal of Bacteriology, November 2009, p. 6701-6708, Vol. 191, No. 21
0021-9193/09/$08.00+0     doi:10.1128/JB.00690-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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