Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
J Bacteriol. 2011 Dec;193(23):6701-11. doi: 10.1128/JB.06124-11. Epub 2011 Sep 30.
Chlorosomes are sac-like, light-harvesting organelles that characteristically contain very large numbers of bacteriochlorophyll (BChl) c, d, or e molecules. These antenna structures occur in chlorophototrophs belonging to some members of the Chlorobi and Chloroflexi phyla and are also found in a recently discovered member of the phylum Acidobacteria, "Candidatus Chloracidobacterium thermophilum." "Ca. Chloracidobacterium thermophilum" is the first aerobic organism discovered to possess chlorosomes as light-harvesting antennae for phototrophic growth. Chlorosomes were isolated from "Ca. Chloracidobacterium thermophilum" and subjected to electron microscopic, spectroscopic, and biochemical analyses. The chlorosomes of "Ca. Chloracidobacterium thermophilum" had an average size of ∼100 by 30 nm. Cryo-electron microscopy showed that the BChl c molecules formed folded or twisted, sheet-like structures with a lamellar spacing of ∼2.3 nm. Unlike the BChls in the chlorosomes of the green sulfur bacterium Chlorobaculum tepidum, concentric cylindrical nanotubes were not observed. Chlorosomes of "Ca. Chloracidobacterium thermophilum" contained a homolog of CsmA, the BChl a-binding, baseplate protein; CsmV, a protein distantly related to CsmI, CsmJ, and CsmX of C. tepidum, which probably binds a single [2Fe-2S] cluster; and five unique polypeptides (CsmR, CsmS, CsmT, CsmU, and a type II NADH dehydrogenase homolog). Although "Ca. Chloracidobacterium thermophilum" is an aerobe, energy transfer among the BChls in these chlorosomes was very strongly quenched in the presence of oxygen (as measured by quenching of fluorescence emission). The combined analyses showed that the chlorosomes of "Ca. Chloracidobacterium thermophilum" possess a number of unique features but also share some properties with the chlorosomes found in anaerobic members of other phyla.
类囊体是囊状的、光捕获细胞器，其特征是含有非常大量的细菌叶绿素 (BChl) c、d 或 e 分子。这些天线结构存在于一些绿菌门和绿弯菌门的光合营养生物以及新近发现的酸杆菌门成员“嗜热脱铁杆菌 Ca. Chloracidobacterium thermophilum”中。“Ca. Chloracidobacterium thermophilum”是第一个被发现拥有类囊体作为光捕获天线进行光合作用生长的需氧生物。从“Ca. Chloracidobacterium thermophilum”中分离出类囊体，并进行电子显微镜、光谱和生化分析。“Ca. Chloracidobacterium thermophilum”的类囊体平均大小约为 100nm×30nm。低温电子显微镜显示，BChl c 分子形成折叠或扭曲的片状结构，层间距约为 2.3nm。与绿硫细菌 Chlorobaculum tepidum 的类囊体中的 BChls 不同，没有观察到同心圆柱纳米管。“Ca. Chloracidobacterium thermophilum”的类囊体含有 CsmA 的同源物，CsmA 是结合 BChl a 的基片蛋白；CsmV，一种与绿硫细菌的 CsmI、CsmJ 和 CsmX 关系较远的蛋白，可能结合单个[2Fe-2S]簇；和五个独特的多肽（CsmR、CsmS、CsmT、CsmU 和一种 II 型 NADH 脱氢酶同源物）。尽管“Ca. Chloracidobacterium thermophilum”是需氧生物，但这些类囊体中的 BChl 之间的能量转移在氧气存在下被强烈猝灭（通过荧光发射猝灭来测量）。综合分析表明，“Ca. Chloracidobacterium thermophilum”的类囊体具有许多独特的特征，但也与其他门的厌氧成员中发现的类囊体具有一些共同的特性。
