REU: Chemotaxis in Soil Rhizosphere and Symbiotic Infection

趋化性是细菌探测重要生物的过程。 营养物质、毒物和其他物质， 从它们的源头游出来 分子、细胞和 已经研究了涉及趋化性的遗传机制 广泛存在于少数细菌如E.杆菌 但 事实上还没有研究过趋化性 有助于细菌的生存和竞争成功 自然环境中的物种。 趋化性是一种非常 复杂的行为反应 它需要双方的共同- 60多个基因的排序和功能， 细胞能量资源的一个重要部分。 所以 似乎趋化性及其调节是主要的 生活方式和竞争成功的决定因素 细菌 拟议的研究将探讨趋化性在以下方面的作用： 一种特定土壤细菌的生态成功， 日本慢生根瘤菌 B。japonicum是一种农学上 大豆重要共生体。 它刺激了 细菌将空气中的氮转化为氮的根瘤 转化为氨，供植物在共生交换中固碳 植物通过光合作用。 结核的形成 取决于细菌在土壤中生存的能力， 没有宿主，它的探测能力，到达能力， 在宿主的根表面定居， 表面的几个根细胞， 易受感染。 趋化性对这些步骤的贡献将 追究 先前的研究表明， 具有缺陷趋化性的突变体显著较少 有效地形成结节。 相反，突变体 增强的趋化性是更有效的结瘤剂。 突变 几个根瘤形成所需的基因 消除一些趋化反应。 在进一步的研究中， 的B。增强、改变或功能障碍 趋化性将被分离、表征和比较， 与亲本菌株的混合物，以确定 趋化性对土壤存活、根 定植和共生感染。 长期目标是 了解趋化性如何有助于成功处理 复杂、动态环境的需求，并利用这一点 提高植物共生性能的知识- 相关细菌

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.