Electron transfer and early evolution of photosynthesis in newly isolated green filamentous bacteria

分离鉴定了卡氏弯折藻（Roseiflexus（R）castenholzii）光化学反应中心复合体，该复合体属于丝状不产氧光合细菌（绿色丝状细菌），但缺少叶绿体。此外，还对编码RC亚基和捕光蛋白的基因进行了克隆和测序。RC复合物由L、M和细胞色素亚基组成。细胞色素亚基的分子量约为35 kDa，含有血红素C，并作为电子供体的光氧化的特殊对细菌叶绿素（BChl）在RC。RC复合物似乎含有三个分子的BChl和三个分子的细菌脱镁叶绿素（BPhe），如在来自橙色绿弯藻（Cfl）的RC制剂中。基于RC亚基的氨基酸序列构建的系统发育树表明，在丝状不产氧光合细菌从紫色细菌分化之后，卡氏红球藻很早就从橙色Cfl.aurantiacus分化出来。虽然卡氏红球藻与橙色Cfl.aurantiacus有亲缘关系，但其puf基因的排列顺序与橙色Cfl.aurantiacus不同，而与紫色细菌的puf基因排列顺序相似，依次为puf B、-A、-L、-M和-C。由于卡氏弯孢霉的光合机构和基因具有介于紫色细菌和橙黄梭菌之间的中间特征，因此它们可能保留了紫色细菌和丝状不产氧光合细菌共同祖先的许多特征。

The photochemical reaction center (RC) complex of Roseiflexus (R) castenholzii, which belongs to filamentous anoxygenic phototrophic bacteria (green filamentous bacteria) but lacks chlorosomes was isolated and characterized. The genes coding for the subunits of RC and the light-harvesting proteins were also cloned and sequenced. The RC complex was composed of L, M and cytochrome subunits. The cytochrome subunit showed a molecular mass of approximately 35 kDa, contained hemes c, and worked as the electron donor to the photooxidized special pair of bacteriochlorophyll (BChl) in the RC. The RC complex appeared to contain three molecules of BChl and three molecules of bacteriopheophytin (BPhe) as in the RC preparation from chloroflexus (Cfl) aurantiacus. The phylogenetic trees based on the deduced amino acid sequences of the RC subunits suggested that R.castenholzii had diverged from Cfl.aurantiacus very early after the divergence of filamentous anoxygenic phototrophic bacteria from purple bacteria. Although R.castenholzii is phylogenetically related to Cfl.aurantiacus, the arrangement of its puf genes, which code for the light-harvesting and the RC subunits, was different from that of Cfl.aurantiacus and similar to those in purple bacteria in the order of puf B, -A, -L, -M, and -C. Since the photosynthetic apparatus and genes of R.castenholzii have intermediary characteristics between purple bacteria and Cfl.aurantiacus, it is likely that they retain many features of the common ancestor of purple bacteria and filamentous anoxygenic phototrophic bacteria.