Cell-Cell Communication and Gene Regulation by Quorum Sensing in the Symbiotic Nitrogen-Fixing Bacterium Rhizobium leguminosarum

共生固氮细菌豆根瘤菌中细胞间通讯和群体感应的基因调控

• 批准号: 9600766
• 负责人: Kendall Gray
• 金额: $ 28.53万
• 依托单位: University of South Florida
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-08-01 至 2001-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9600766&HistoricalAwards=false
• 关键词: Cell; Communication; Gene; Regulation; Quorum

9600766 Gray The purpose of this research is to characterize the quorum sensing regulatory system of the symbiotic nitrogen-fixing bacterium Rhizobium leguminosarum. Quorum sensing is a conserved mechanism of population density-dependent gene activation in Gram-negative bacteria. In quorum sensing, a self-produced extracellular signal molecule called autoinducer interacts with a transcriptional activator protein to activate the expression of specific genes. R. Ieguminosarum produces a unique autoinducer that, together with the transcriptional activator RhiR, activates an operon of rhizosphere-expressed genes (rhiABC) and an unidentified locus that causes an inhibition of cell growth. Both rhiR and rhiABC are encoded by Sym plasmids unique to pea-nodulating biovars of R. Ieguminosarum. The growth-inhibiting function appears to be unique to one specific isolate of the Sym plasmid, pRLlJI, which also encodes a repressor function that blocks normal production of autoinducer. We have recently discovered two additional R. Ieguminosarum autoinducers, the production of which is unaffected by this pRLlJI-encoded repressor. The newly-identified R. Ieguminosarum signals activate rhiABC with RhiR, but do not activate growth inhibition. We have also discovered a unique autoinducer produced by the related species R. meliloti, for which no function is currently known. The specific objectives of this research are: 1) to characterize the molecular structures of the two newly-identified R. Ieguminosarum autoinducers, as well as the autoinducer produced by R. meliloti; 2) to identify the pRLlJI-encoded gene that blocks autoinducer synthesis and elucidate its mechanism of action; and 3) to investigate the role of quorum sensing in the conjugal transfer of pRLlJI. This research addresses fundamental questions of intercellular communication, environmental sensing, and gene regulation in Rhizobium. Due to the extreme conservation of quorum sensing regulators, the results of this research may have direct ap plications to other symbiotic or pathogenic bacterial systems as well. The results of this work will be integrated into an existing course in Microbial Physiology & Genetics, and represent an essential component in the development of a new course on the biology of Bacteria as Multicellular Organisms. As part of a career commitment to innovative instruction, the P.I. is also developing an independent research exercise as part of the laboratory curriculum for Microbial Physiology & Genetics. %%% Bacteria of the genus Rhizobium are of considerable ecological and economic importance as a biological source of fixed nitrogen. These bacteria typically form complex symbiotic associations with the roots of specific host plants such as peas and alfalfa. This research project is an investigation into the molecular aspects of intercellular signaling, cell-cell communication, and gene activation in one species of Rhizobium, R. Ieguminosarum. The molecular structures of specific gene-activating signal molecules produced by the bacteria will be determined, and the genes that regulate production of these different signals will be studied. The possible role of these signal molecules in mediating genetic exchange among populations of bacteria will also be determined. The results of this work should increase our understanding of the regulatory biology of these important bacteria and provide new insights into the effects of extracellular signals on their symbiotic lifestyle. ***

9600766灰色本研究的目的是对共生固氮菌豆科根瘤菌的群体感应调控系统进行表征。群体感应是革兰氏阴性菌群体密度依赖性基因激活的一种保守机制。在群体感应中，一种自身产生的胞外信号分子，称为自动诱导剂，与转录激活蛋白相互作用，激活特定基因的表达。Iegumosarum产生一种独特的自我诱导剂，与转录激活剂RhiR一起激活根际表达基因的操纵子(RhiABC)和导致细胞生长抑制的未知基因位点。RhiR和rhiABC均由豌豆结瘤生物群所特有的Sym质粒编码。生长抑制功能似乎是Sym质粒的一个特定分离物pRLlJI所独有的，它也编码一种阻遏功能，阻止自动诱导剂的正常生产。我们最近发现了另外两个Iegumomosarum自身诱导子，其生产不受这个pRLlJI编码的阻遏子的影响。新发现的发光菌信号可激活带有RhiR的rhiABC，但不能激活生长抑制。我们还发现了一种由近缘物种紫花苜蓿产生的独特的自我诱导剂，目前尚不清楚其功能。本研究的具体目的是：1)鉴定两个新发现的Iegnuosarum自身诱导子的分子结构；2)鉴定阻止自身诱导子合成的pRL1JI编码基因，并阐明其作用机制；3)研究群体感应在pRLlJI共生转移中的作用。这项研究解决了根瘤菌的细胞间通讯、环境感知和基因调控等基本问题。由于群体感应调节子的极端保守性，本研究结果可能也直接应用于其他共生或致病细菌系统。这项工作的结果将被整合到现有的微生物生理学和遗传学课程中，并代表着作为多细胞有机体的细菌生物学新课程开发的重要组成部分。作为对创新教学事业承诺的一部分，P.I.还开发了一项独立的研究练习，作为微生物生理学与遗传学实验室课程的一部分。根瘤菌属的细菌作为固定氮的生物来源具有相当重要的生态和经济价值。这些细菌通常与豌豆和紫花苜蓿等特定寄主植物的根形成复杂的共生关系。本研究是对小麦根瘤菌的细胞间信号转导、细胞间通讯和基因激活的分子方面的研究。将确定细菌产生的特定基因激活信号分子的分子结构，并研究调节这些不同信号产生的基因。这些信号分子在调节细菌种群之间的遗传交换方面的可能作用也将被确定。这项工作的结果应该会增加我们对这些重要细菌的调节生物学的理解，并为细胞外信号对它们共生生活方式的影响提供新的见解。***