Control of Heterocyst Differentiation in Free-Living and Symbiotic Cyanobacteria

该项目的目的是确定Nostoc spp中控制营养细胞分化为异囊（需氧固氮位点）的生化机制。Meeks博士假设，在自由生活状态下，异囊的分化受到全球氮调节系统的控制。当Nostoc与苔藓植物anthoceros结合时，可能被共生的特定系统所取代。他建议继续鉴定和互补-鉴定和分离参与杂种囊分化的调控基因。具体目标包括分离具有多效表型的突变体，这些突变体不能以硝酸盐和N2作为氮源生长，但能够在共生中固定N2。这些突变体将通过分析可逆（单位点抑制突变）的类别来表征。突变表型将通过共轭转移在大肠杆菌中克隆的野生型或“反向”DNA或在体外包装的质粒中通过电穿孔转移到Nostoc受体中来补充。将对互补片段进行排序，并与已建立的数据库进行比较。它们还将用于野生型和突变菌株的生理遗传学研究，以确定它们在分化中的作用。这项研究对两个方面有影响。首先，它是细菌中模式形成的罕见例子，因此为利用细菌系统中可用的强大遗传技术进行研究提供了一个例子。此外，蓝藻是环境的重要组成部分，作为还原碳和氮的主要生产者发挥着独特的作用。因此，了解这些过程是如何控制的具有普遍的重要性。

The intent of the project is to identify the biochemical mechanisms that control the differentiation of vegetative cells into heterocysts (sites of aerobic nitrogen fixation) in Nostoc spp. Dr. Meeks hypothesizes that heterocyst differentiation is under control of a global nitrogen regulatory system in the free- living state, that may be superseded by a symbiotic specific system when Nostoc is in association with the bryophyte anthoceros. He proposes to continue characterization and complementation - to identify and isolate regulatory genes involved in heterocyst differentiation. The specific objectives include isolation of additional mutants with the pleiotropic phenotype of inability to grow with nitrate and N2 as nitrogen sources, but able to fix N2 in symbiosis. Such mutants will be characterized by analysis of classes of revertant (single site suppressor mutations). The mutant phenotypes will be complemented by conjugational transfer of wild type or "revertant" DNA cloned in E. coli or packaged in vitro in plasmids and transferred into the Nostoc recipient by electroporation. complementing fragments will be sequenced and compared to established data banks. They will also be used in physiological genetic studies with wild type and mutant strains of Nostoc to define their role in differentiation. %%% This study has implications for two areas. First it is a rare example of pattern formation in bacteria and therefore provides an example to study with the powerful genetic techniques available in bacterial system. Additionally, the cyanobacteria are important components of the environment and play a unique role as primary producers of reduced carbon and nitrogen. An understanding of how these processes are controlled is therefore of general importance.