REU: Chemotaxis in Soil Rhizosphere and Symbiotic Infection

REU：土壤根际的趋化性和共生感染

• 批准号: 8819789
• 负责人: Wolfgang Bauer
• 金额: --
• 依托单位: Ohio State University Research Foundation -DO NOT USE
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 1989
• 资助国家: 美国
• 起止时间: 1989-05-01 至 1993-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8819789&HistoricalAwards=false
• 关键词: REU; Chemotaxis; Soil; Rhizosphere; Symbiotic

Chemotaxis is the process by which bacteria detect important nutrients, poisons and other substances and move toward or away from their source by swimming. The molecular, cellular and genetic mechanisms involved in chemotaxis have been studied extensively in a few bacteria such as E. coli. However, there has been virtually no work done to determine how chemotaxis contributes to the survival and competitive success of bacterial species in natural environments. Chemotaxis is a very sophisticated behavioral response. It requires both the co- ordination and functioning of over 60 genes and the expenditure of a significant fraction of the cell's energy resources. So it seems likely that chemotaxis and its regulation are major determinants of lifestyle and competitive success for many bacteria. The proposed studies will explore the role of chemotaxis in the ecological success of a particular soil bacterium, Bradyrhizobium japonicum. B. japonicum is an agronomically important symbiont of soybean. It stimulates the formation of nodules in which the bacterium converts nitrogen from the air into ammonia for the plant in symbiotic exchange for carbon fixed by the plant through photosynthesis. Formation of nodules depends on the ability of the bacterium to survive in the soil in the absence of its host, its ability to detect, reach and colonize the root surface of its host, and its ability to get to those few root cells on the surface that are developmentally susceptible to infection. The contribution of chemotaxis to each of these steps will be investigated. Previous studies have shown that bacterial mutants which have defective chemotaxis are significantly less efficient in nodule formation. Conversely, mutants with enhanced chemotaxis are more efficient nodulators. Mutations in several of the genes required for nodule formation specifically abolish some chemotactic responses. In further studies, mutants of B. japonicum with enhanced, altered or disfunctional chemotaxis will be isolated, characterized and compared in mixtures with the parental strain to determine which aspects of chemotaxis contribute importantly to soil survival, root colonization and symbiotic infection. Long range goals are to understand how chemotaxis contributes to success in dealing with the demands of complex, dynamic environments and to use this knowledge to enhance the symbiotic performance of plant- associated bacteria.

趋化性是细菌探测到重要的营养物质、毒素和其他物质，并通过游动来接近或远离它们的来源的过程。趋化性的分子、细胞和遗传机制在大肠杆菌等少数细菌中得到了广泛的研究。然而，在确定趋化性如何促进细菌物种在自然环境中的生存和竞争成功方面，几乎没有做过任何工作。趋化是一种非常复杂的行为反应。它既需要60多个基因的协调和运作，也需要细胞能量资源的很大一部分的消耗。因此，趋化性及其调控似乎是许多细菌生活方式和竞争成功的主要决定因素。提出的研究将探讨趋化作用在生态成功的一个特定的土壤细菌，缓生根瘤菌日本。日本芽孢杆菌是一种重要的大豆共生体。它刺激结核的形成，细菌将空气中的氮转化为植物的氨，通过光合作用与植物固定的碳进行共生交换。结核的形成取决于细菌在没有宿主的情况下在土壤中生存的能力，它探测、到达和定植宿主根表面的能力，以及它到达表面上那些少数易受感染的根细胞的能力。我们将研究趋化性对这些步骤的贡献。先前的研究表明，具有趋化性缺陷的细菌突变体在结核形成方面的效率显着降低。相反，具有增强趋化性的突变体是更有效的调节剂。结节形成所需的几个基因的突变特别地取消了一些趋化反应。在进一步的研究中，将分离出趋化性增强、改变或功能失调的日本白僵菌突变体，对其进行鉴定，并与亲本菌株混合进行比较，以确定趋化性的哪些方面对土壤存活、根定植和共生感染有重要影响。长期目标是了解趋化性如何有助于成功应对复杂、动态环境的需求，并利用这些知识来提高植物相关细菌的共生性能。