Biology of the N2-fixing soil bacterium, Sinorhizobium meliloti

土壤细菌Sinorhizobium meliloti在紫花苜蓿的根上形成固氮根瘤。固氮对农业具有重要意义，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常常受到可用磷(P)（主要以无机磷酸盐（Pi）的形式存在）的数量的限制。在本提案中，我们概述了研究的重点是细菌如何将Pi运输到它们的细胞中，以及细菌如何感知Pi并在Pi限制生长时做出反应和生存。我们将研究一种被称为papi - pit的Pi传输系统，它存在于许多细菌中。这个系统是如何运作的，特别是Pap蛋白的作用是什么还不清楚。我们提出Pap调节或控制Pit转运蛋白的活性，我们进行实验来解决这一假设。另一种蛋白PhoU与Pap在结构上有一定的相似性，我们将研究PhoU是否控制一种名为PstSCAB的Pi转运蛋白，以及该系统如何参与感知细胞的“Pi状态”。S. meliloti的基因组是不寻常的，因为除了一条染色体（3.7 Mb）外，它还有两个巨型质粒，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（占基因组的40%）的丢失如何影响这些细胞中碳和Pi代谢的整合。

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.