Novel aspects of quorum-sensing signal transduction in Pantoea stewartii

智力优势：群体感应是一种过程，它使一组单细胞细菌能够计算自己的数量，并基于细胞密度，通过细胞间通信以协调的方式行动。一种通过群体感应反应进行交流的细菌是植物病原体泛菌（Pantoea stewartii subsp）。stewartii。这种微生物导致甜玉米和玉米的斯图尔特枯萎病，从而对这些重要的美国农产品的生产产生负面影响。枯萎病是细菌产生的细胞外囊或黏液层阻塞植物的水输送管道的结果。这种胶囊材料的生产是由群体感应控制的。群体感应反应涉及由细菌产生的细胞外信号分子，称为酰基高丝氨酸内酯（AHL）和AHL的细胞受体蛋白，称为EsaR。EsaR在低细胞密度时抑制细胞外胶囊的产生，但在高细胞密度时被AHL灭活，导致胶囊合成的抑制。这种控制AHL的机制在细菌群体感应调节蛋白中是不典型的，人们对其了解甚少。在已知的50多种细菌群体感应系统中，大多数仅在高细胞密度下起作用，此时AHL信号分子也以高浓度存在。最近，PI证明了不含ahl的EsaR也可以在低细胞密度下激活基因表达，这也是与其他系统相比，P. stewartii群体感应的一个独特方面。这里的项目是测试EsaR在P. stewartii中既作为激活剂又作为抑制剂的假设。该项目的具体目标是：(1)阐明EsaR以与大多数群体感应调节剂相反的方式响应其配体AHL的机制；(2)确定EsaR控制不是一个，而是两个信号转导途径的目标和方式，一个在低细胞密度下，另一个在高细胞密度下。这些研究的结果将改变一些公认的群体感应调节剂的范例，以及它们协调细菌基因表达变化的方式。对EsaR及其控制的基因的研究还将使人们更好地了解植物致病性感染的阶段，并有可能揭示未来疾病控制的可能途径。对研究生和本科生的研究培训和指导是该项目的重中之重。学生将接受科学方法和科学伦理方面的训练。学生将在专业发展的其他方面得到培养，例如在科学会议上发表演讲，学习以协同的方式相互合作和与合作者合作。最终，这些初级科学家将毕业并继续成为科学界富有成效的成员。为了使这个社区更加多样化，将努力征聘、指导和保留妇女和代表性不足的少数民族加入研究小组，并为他们维持一个支持性的工作环境。作为个人，PI积极致力于改善弗吉尼亚理工大学的微生物学/免疫学课程，并担任个人学生和本科微生物学俱乐部的学术顾问。该俱乐部在地区托儿所、小学和校友活动中开展教育推广活动，教导家长和孩子们微生物在日常生活中的重要性。

Intellectual Merit: Quorum sensing is a process that enables a group of single-celled bacteria to count their numbers and, based on cell density, behave in a coordinated manner through cell-cell communication. One bacterium that communicates through a quorum-sensing response is the plant pathogen Pantoea stewartii subsp. stewartii. This organism causes Stewart's wilt disease in sweet corn and maize, and thus has a negative impact on production of these important US agricultural commodities. The wilt is a consequence of the extracellular capsule or slime layer produced by the bacteria that blocks the water transport vessels of the plant. Production of this capsular material is controlled by quorum sensing. The quorum-sensing response involves extracellular signaling molecules made by the bacteria that are called acyl homoserine lactones (AHL) and a cellular receptor protein for the AHL called EsaR. EsaR represses production of the extracellular capsule at low cell density, but is inactivated by AHL at high cell density resulting in derepression of capsule synthesis. This mechanism of AHL control is atypical amongst bacterial quorum sensing regulatory proteins and is poorly understood. Most of the over fifty known bacterial quorum-sensing systems function only at high cell density, when the AHL signaling molecule is also present at high concentration. Recently the PI demonstrated that AHL-free EsaR can also activate gene expression at low cell density which is also a unique aspect of quorum sensing in P. stewartii in comparison to other systems. The project here is to test the hypothesis that EsaR acts both as an activator and as a repressor in P. stewartii. The specific aims of the project are to (1) elucidate the mechanism whereby EsaR responds to its ligand AHL in a manner opposite to that of the majority of quorum-sensing regulators and (2) determine the targets and the manner whereby EsaR controls not one, but two signal transduction pathways, one at low cell density and another at high cell density. Results from these studies will transform some accepted paradigms of quorum sensing regulators and the manner in which they coordinate changes in bacterial gene expression. Studies of EsaR and the genes it controls will also lead to a better understanding of the stages of pathogenic infections in plants, and are also likely to reveal possible avenues for disease control in the future.Broader Impact Research training and mentoring of graduate and undergraduate students are top priorities of this project. Students will be trained in the methods of science as well as in scientific ethics. Students will be nurtured in other aspects of their professional development, such as giving presentations at scientific conferences and learning to work in a synergistic manner with each other and with collaborators. Ultimately, these junior scientists will graduate and move on to become productive members of the scientific community. To bring more diversity to this community, efforts will be made to recruit, mentor and retain women and underrepresented minorities to the research group and to maintain a supportive working environment for them. As an individual, the PI is actively engaged in improving the microbiology/immunology curriculum at Virginia Tech and serving as an academic advisor to individual students as well as to the undergraduate microbiology club. The club performs educational outreach at regional daycares, elementary schools and alumni events, teaching parents and children about the importance of microorganisms in their daily lives.