Genetic manipulation of carotenoid biosynthesis in the green sulfur bacterium Chlorobium tepidum
Genetic manipulation of carotenoid biosynthesis in the green sulfur bacterium Chlorobium tepidum
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DOI：
10.1128/jb.186.16.5210-5220.2004
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发表时间：
2004-08-01
影响因子：
3.2
通讯作者：
Bryant, DA
中科院分区：
文献类型：
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作者：
Frigaard, NU;Maresca, JA;Bryant, DA
绿色硫磺细菌特氏氯杆菌是一种严格的厌氧菌和专性光自养细菌。根据与已知酶或序列基序的相似性，在毛滴虫基因组序列中鉴定出9个编码类胡萝卜素生物合成酶的开放阅读框，并且所有9个基因都失活。通过对突变体中类胡萝卜素组成的分析，可以鉴定出编码以下六种酶的基因：植烯合成酶(crtB/CT1386)、植烯脱饱和酶(CrtPICT0807)、zeta-胡萝卜素脱饱和酶(crtQ/CT1414)、γ-胡萝卜素脱饱和酶(crtU/CT0323)、类胡萝卜素1‘，2’-水解酶(CRTC/CT0301)和类胡萝卜素顺反异构酶(crtH/CT0649)。三个突变体(CT0180、CT1357和CT1416突变体)没有表现出明显的表型。苔藓中类胡萝卜素的生物合成途径与蓝藻和植物中的类似，是通过两个类植物脱饱和酶(CrtP和CrtQ)和类植物类顺反异构酶(CrtH)将植酸转化为番茄红素，因此不同于所有其他细菌中已知的途径。与蓝藻和植物中的情况相反，构建完全缺乏类胡萝卜素的crtB突变体表明，类胡萝卜素对绿色硫磺细菌的光合作用生长不是必需的。然而，缺乏有色类胡萝卜素的突变体(crtB、crtP和crtQ突变体)的细菌叶绿素a含量低于野生型，并且这些突变体在所有测试的光强下都表现出明显的生长速率缺陷。因此，有色类胡萝卜素在绿色硫磺细菌中可能既具有结构保护作用，又具有光保护作用。能够如此戏剧性地操纵被盖隐翅虫的类胡萝卜素成分，为研究类胡萝卜素在捕光绿小体天线和铁-硫型(类光天冬氨酸I类)反应中心中的作用提供了极好的可能性。对绿硫菌和绿丝状菌中类胡萝卜素产生酶的系统发育进行了讨论。
The green sulfur bacterium Chlorobium tepidum is a strict anaerobe and an obligate photoautotroph. On the basis of sequence similarity with known enzymes or sequence motifs, nine open reading frames encoding putative enzymes of carotenoid biosynthesis were identified in the genome sequence of C. tepidum, and all nine genes were inactivated. Analysis of the carotenoid composition in the resulting mutants allowed the genes encoding the following six enzymes to be identified: phytoene synthase (crtB/CT1386), phytoene desaturase (crtPICT0807), zeta-carotene desaturase (crtQ/CT1414), gamma-carotene desaturase (crtU/CT0323), carotenoid 1',2'-hydratase (crtC/CT0301), and carotenoid cis-trans isomerase (crtH/CT0649). Three mutants (CT0180, CT1357, and CT1416 mutants) did not exhibit a discernible phenotype. The carotenoid biosynthetic pathway in C. tepidum is similar to that in cyanobacteria and plants by converting phytoene into lycopene using two plant-like desaturases (CrtP and CrtQ) and a plant-like cis-trans isomerase (CrtH) and thus differs from the pathway known in all other bacteria. In contrast to the situation in cyanobacteria and plants, the construction of a crtB mutant completely lacking carotenoids demonstrates that carotenoids are not essential for photosynthetic growth of green sulfur bacteria. However, the bacteriochlorophyll a contents of mutants lacking colored carotenoids (crtB, crtP, and crtQ mutants) were decreased from that of the wild type, and these mutants exhibited a significant growth rate defect under all light intensities tested. Therefore, colored carotenoids may have both structural and photoprotection roles in green sulfur bacteria. The ability to manipulate the carotenoid composition so dramatically in C. tepidum offers excellent possibilities for studying the roles of carotenoids in the light-harvesting chlorosome antenna and iron-sulfur-type(photosystern I-like) reaction center. The phylogeny of carotenogenic enzymes in green sulfur bacteria and green filamentous bacteria is also discussed.