Comparison of the physical characteristics of chlorosomes from three different phyla of green phototrophic bacteria

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• 作者：Peter G. Adams ; Ashley J. Cadby ; Benjamin Robinson ; Yusuke Tsukatani ; Marcus Tank ; Jianzhong Wen ; Robert E. Blankenship ; Donald A. Bryant ; C. Neil Hunter
• 关键词：AFM ; atomic force microscopy ; BChl(s) ; bacteriochlorophyll(s) ; Ca ; Chloracidobacterium ; Cab. ; Chloroacidobacterium ; Cba. ; Chlorobaculum ; Cfx. ; Chloroflexus ; EM ; electron microscopy ; FAP ; filamentous anoxygenic phototrophs ; FWHM ; full width at half maximum
• 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：1827
• 期：10
• 页码：1235-1244
• 全文大小：2038 K

文摘

Chlorosomes, the major antenna complexes in green sulphur bacteria, filamentous anoxygenic phototrophs, and phototrophic acidobacteria, are attached to the cytoplasmic side of the inner cell membrane and contain thousands of bacteriochlorophyll (BChl) molecules that harvest light and channel the energy to membrane-bound reaction centres. Chlorosomes from phototrophs representing three different phyla, Chloroflexus (Cfx.) aurantiacus, Chlorobaculum (Cba.) tepidum and the newly discovered ¡°Candidatus (Ca.) Chloracidobacterium (Cab.) thermophilum¡± were analysed using PeakForce Tapping atomic force microscopy (PFT-AFM). Gentle PFT-AFM imaging in buffered solutions that maintained the chlorosomes in a near-native state revealed ellipsoids of variable size, with surface bumps and undulations that differ between individual chlorosomes. Cba. tepidum chlorosomes were the largest (133 ¡Á 57 ¡Á 36 nm; 141,000 nm³ volume), compared with chlorosomes from Cfx. aurantiacus (120 ¡Á 44 ¡Á 30 nm; 84,000 nm³) and Ca. Cab. thermophilum (99 ¡Á 40 ¡Á 31 nm; 65,000 nm³). Reflecting the contributions of thousands of pigment-pigment stacking interactions to the stability of these supramolecular assemblies, analysis by nanomechanical mapping shows that chlorosomes are highly stable and that their integrity is disrupted only by very strong forces of 1000-2000 pN. AFM topographs of Ca. Cab. thermophilum chlorosomes that had retained their attachment to the cytoplasmic membrane showed that this membrane dynamically changes shape and is composed of protrusions of up to 30 nm wide and 6 nm above the mica support, possibly representing different protein domains. Spectral imaging revealed significant heterogeneity in the fluorescence emission of individual chlorosomes, likely reflecting the variations in BChl c homolog composition and internal arrangements of the stacked BChls within each chlorosome.