Control of Heterocyst Differentiation in Free-Living and Symbiotic Cyanobacteria

该项目的目的是确定控制发菜营养细胞分化为异形胞(好氧固氮部位)的生化机制。米克斯博士假设，在自由生活状态下，异形胞的分化受到全球氮素调控系统的控制，当念珠藻与苔藓植物花角藻结合时，该系统可能会被共生的特定系统所取代。他建议继续进行定性和互补--识别和分离参与异胞体分化的调控基因。具体目标包括分离更多具有多效性表型的突变株，即不能以硝酸盐和氮气为氮源生长，但能够固定氮气共生。这些突变的特征将通过分析回复突变的类别(单部位抑制突变)来确定。突变的表型将通过接合转移补充野生型或“回复”的DNA在大肠杆菌中克隆或在体外包装在质粒中，并通过电穿孔转移到发菜受体。将对互补片段进行测序，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型发菜的生理遗传学研究，以确定它们在分化中的作用。%这项研究有两个方面的影响。首先，这是细菌中模式形成的罕见例子，因此为研究细菌系统中可用的强大基因技术提供了一个例子。此外，蓝藻是环境的重要组成部分，并作为还原碳和氮的初级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differentiation is under control of a global nitrogen regulatory system in the free- living state, that may be superseded by a symbiotic specific system when Nostoc is in association with the bryophyte anthoceros.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.