Characterization of the chlorosome antenna of the filamentous anoxygenic phototrophic bacterium Chloronema sp. strain UdG9001
Characterization of the chlorosome antenna of the filamentous anoxygenic phototrophic bacterium Chloronema sp. strain UdG9001
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丝状缺氧光养细菌 Chloronema sp 的叶绿体天线的表征。
作者：
F. Gich;R. Airs;M. Danielsen;B. Keely;C. Abella;J. Garcia;Mette Miller;C. Borrego
丝状厌氧光营养细菌Chloronema sp.的吸收和荧光特性对菌株UdG9001进行了分析。绿藻的叶绿体触角由细菌叶绿素d和细菌叶绿素c组成，类胡萝卜素主要为γ-胡萝卜素。结合APCILC-MS/MS分析表明，绿体BChl由一系列高度多样化的同系物组成，这些同系物在C-8和/或C-12处的大环烷基化度和在C-17处酯化为丙酸基的醇部分上都不同。Chloronema中的Bchl c和Bchl d主要与香叶醇(33%)、十七醇(24%)、十八烯醇(19%)、十八醇(14%)和十六烯醇(9%)进行酯化反应。尽管存在这种色素异质性，但在710-740 nm的波长范围内激发时，绿小体的荧光发射显示出以765 nm为中心的单峰。这个单一的发射被分配给Bchl c，表明在同一叶绿体内从Bchl d到Bchl c的能量转移。同样，在还原条件下孵育绿小体导致荧光发射的微弱增加，这表明这是一个小的氧化还原依赖的荧光。最后，利用SDS-PAGE和MALDI-TOF-MS对绿微藻绿小体进行蛋白质分析，发现存在一种分子质量为5.7 kDa的多肽，与橙色绿体和毛壳藻中发现的CSMA蛋白相似。还检测到了几种微小的多肽，但没有鉴定出来。这些结果表明，与丝状厌氧光养细菌和绿色硫磺细菌的其他成员相比，绿藻拥有一种具有新特征的天线系统，这可能是进一步研究的兴趣。
The absorption and fluorescence properties of chlorosomes of the filamentous anoxygenic phototrophic bacterium Chloronema sp. strain UdG9001 were analyzed. The chlorosome antenna of Chloronema consists of bacteriochlorophyll (BChl) d and BChl c together with γ-carotene as the main carotenoid. HPLC analysis combined with APCI LC-MS/MS showed that the chlorosomal BChls comprise a highly diverse array of homologues that differ in both the degree of alkylation of the macrocycle at C-8 and/or C-12 and the alcohol moiety esterified to the propionic acid group at C-17. BChl c and BChl d from Chloronema were mainly esterified with geranylgeraniol (33% of the total), heptadecanol (24%), octadecenol (19%), octadecanol (14%), and hexadecenol (9%). Despite this pigment heterogeneity, fluorescence emission of the chlorosomes showed a single peak centered at 765 nm upon excitation at wavelengths ranging from 710 to 740 nm. This single emission, assigned to BChl c, indicates an energy transfer from BChl d to BChl c within the same chlorosome. Likewise, incubation of chlorosomes under reducing conditions caused a weak increase in fluorescence emission, which indicates a small redox-dependent fluorescence. Finally, protein analysis of Chloronema chlorosomes using SDS-PAGE and MALDI-TOF-MS revealed the presence of a chlorosomal polypeptide with a molecular mass of 5.7 kDa, resembling the CsmA protein found in Chloroflexus aurantiacus and Chlorobium tepidum chlorosomes. Several minor polypeptides were also detected but not identified. These results indicate that, compared with other members of filamentous anoxygenic phototrophic bacteria and green sulfur bacteria, Chloronema possesses an antenna system with novel features that may be of interest for further investigations.