Biology of the N2-fixing soil bacterium, Sinorhizobium meliloti

土壤细菌苜蓿中华根瘤菌（Sinorhizobium meliloti）在苜蓿根部形成固氮根瘤。固氮对农业具有巨大的意义，因为它绕过了与氮肥相关的经济和环境成本。 除了氮（N）之外，植物和微生物的生长通常受到有效磷（P）（主要以无机磷酸盐（Pi）的形式存在）的量的限制。 在这项提案中，我们概述了一些研究，这些研究主要集中在细菌如何将Pi转运到细胞中，以及细菌如何感知Pi并在Pi限制生长时做出反应和生存。 我们将研究一种名为Pap-Pit的Pi运输系统，该系统存在于许多细菌中。 这个系统是如何运作的，特别是Pap蛋白的作用尚不清楚。 我们建议巴氏杆菌调节或控制的Pit转运蛋白的活性，我们进行实验，以解决这一假设。 另一种蛋白质PhoU与Pap有一些结构相似性，我们将研究PhoU是否控制一种称为PstSCAB的不同Pi转运蛋白，以及该系统如何参与感知细胞的“Pi状态”。 色葡萄苜蓿基因组是不寻常的，因为除了染色体（3.7 Mb），它有两个大质粒称为pSymA（1.4 Mb）和pSymB（1.7 Mb）。 我们将研究巨质粒在Pi利用中的作用，以及这些巨质粒（基因组的40%）的丢失如何影响这些细胞中碳和Pi代谢的整合。 这项研究将增加我们对微生物在营养不良环境中生长和生存过程的理解。 这具有高度的经济和环境意义，因为许多农业生产受到Pi的可用性的限制，并且Pi污染导致我们的水系统的富营养化。 这项研究将由研究生和本科生进行，这些学生将获得分子遗传学和微生物学方面的高水平技术专业知识，可应用于包括生物技术在内的许多领域。 此外，学生将接受沟通，项目管理，撰写报告，安全程序和团队环境中工作的大量培训。

The soil bacterium, Sinorhizobium meliloti, forms N2-fixing nodules on the roots of alfalfa. N2-fixation is of huge significance to agriculture as it by-passes the economic and environmental costs associated with nitrogen fertilizer. In addition to nitrogen (N), the growth of plants and microorganisms is often limited by the amount of available phosphorus (P) (primarily present as inorganic phosphate (Pi)). In this proposal we outline studies that focused on how bacteria transport Pi into their cells and how bacteria sense Pi and respond and survive when Pi is limiting growth. We will study a Pi transport system called Pap-Pit that is present in many bacteria. How this system functions, and particularly what is the role of the Pap protein is not known. We propose that Pap modulates or controls the activity of the Pit transport protein and we perform experiments to address this hypothesis. Another protein, PhoU, has some structural similarity to Pap, and we will investigate whether PhoU controls a different Pi transporter called PstSCAB and how this system is involved in sensing the cellular "Pi-status". The S. meliloti genome is unusual, as in addition to a chromosome (3.7 Mb), it has two megaplasmids called pSymA (1.4 Mb) and pSymB (1.7 Mb). We will investigate the role of the megaplasmids in Pi utilization and how loss of these megaplasmids (40% of the genome) affects the integration of carbon and Pi metabolism in these cells. This research will increase our understanding of processes microorganisms employ to grow and survive in nutrient poor environments. This has high economic and environmental significance since much agricultural production is limited by availability of Pi, and Pi pollution causes eutrophication of our water systems. This research will be performed by graduate students and undergraduate student and these students will acquire high level technical expertise in molecular genetics and microbiology that can be applied in many areas including biotechnology. In addition, the students will receive much training in communication, project management, writing reports, safety procedures and working in a team environment.