Yildiz F H, Gest H, Bauer C E
Department of Biology, Indiana University, Bloomington 47405.
J Bacteriol. 1991 Jul;173(13):4163-70. doi: 10.1128/jb.173.13.4163-4170.1991.
A genetic system has been developed for studying bacterial photosynthesis in the recently described nonsulfur purple photosynthetic bacterium Rhodospirillum centenum. Nonphotosynthetic mutants of R. centenum were obtained by enrichment for spontaneous mutations, by ethyl methanesulfonate mutagenesis coupled to penicillin selection on solid medium, and by Tn5 transposition mutagenesis with an IncP plasmid vector containing a temperature-sensitive origin of replication. In vivo and in vitro characterization of individual strains demonstrated that 38 strains contained mutations that blocked bacteriochlorophyll a biosynthesis at defined steps of the biosynthetic pathway. Collectively, these mutations were shown to block seven of eight steps of the pathway leading from protoporphyrin IX to bacteriochlorophyll a. Three mutants were isolated in which carotenoid biosynthesis was blocked early in the biosynthetic pathway; the mutants also exhibited pleiotropic effects on stability or assembly of the photosynthetic apparatus. Five mutants failed to assemble a functional reaction center complex, and seven mutants contained defects in electron transport as shown by an alteration in cytochromes. In addition, several regulatory mutants were isolated that acquired enhanced repression of bacteriochlorophyll in response to the presence of molecular oxygen. The phenotypes of these mutants are discussed in relation to those of similar mutants of Rhodobacter and other Rhodospirillum species of purple photosynthetic bacteria.
已开发出一种遗传系统，用于研究最近描述的非硫紫色光合细菌百脉根红螺菌（Rhodospirillum centenum）中的细菌光合作用。通过富集自发突变、用甲磺酸乙酯诱变并结合在固体培养基上的青霉素选择，以及用含有温度敏感复制起点的IncP质粒载体进行Tn5转座诱变，获得了百脉根红螺菌的非光合突变体。对各个菌株的体内和体外特性进行表征表明，38个菌株含有在生物合成途径特定步骤阻断细菌叶绿素a生物合成的突变。总的来说，这些突变被证明阻断了从原卟啉IX到细菌叶绿素a的途径的八个步骤中的七个。分离出三个突变体，其中类胡萝卜素生物合成在生物合成途径早期被阻断；这些突变体还对光合装置的稳定性或组装表现出多效性影响。五个突变体未能组装功能性反应中心复合物，七个突变体如细胞色素改变所示在电子传递方面存在缺陷。此外，分离出几个调节突变体，它们在分子氧存在下对细菌叶绿素的抑制作用增强。将这些突变体的表型与红杆菌属（Rhodobacter）和其他紫色光合细菌红螺菌属物种的类似突变体的表型进行了讨论。
