POWRE: Phylogeny of Heterocystous Cyanobacteria and Evolution of nitrogen Fixation Genes

POWRE：异囊蓝藻的系统发育和固氮基因的进化

• 批准号: 9973340
• 负责人: Susan Barnum
• 金额: $ 7.5万
• 依托单位: Miami University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-15 至 2001-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9973340&HistoricalAwards=false
• 关键词: POWRE; Phylogeny; Heterocystous; Cyanobacteria; Evolution

Barnum 9973340Cyanobacteria are a diverse group of oxygen-producing, photosynthetic bacteria that inhabit virtually every major aquatic and terrestrial biome - desert, freshwater and marine, including hot springs and sub-Arctic and Antarctic regions. Cyanobacteria are particularly important in poor soils and nutrient-depleted regions and are the major suppliers of fixed nitrogen through the process of nitrogen fixation. Some species form symbiotic relationships with various plant species and directly provide nitrogen for uptake by plants. Cyanobacteria have an ancient history dating back almost 3.5 billion years. They diversified extensively to become some of the most successful and ecologically significant organisms on Earth, with respect to longevity of the lineage and impact on the Earth's early environment. It is widely believed that cyanobacteria were responsible for the conversion of the Earth's anaerobic atmosphere to an aerobic one via oxygenic photosynthesis - a pivotal event that led to the evolution of diverse life on Earth. While carbon dioxide fixation, through photosynthesis, arose early in the evolution of organisms, it is not known when nitrogen fixation first occurred. Since nitrogen fixation enzymes are irreversibly inactivated by oxygen, it has been proposed that nitrogen fixation is an ancient process that existed before the Earth's atmosphere became aerobic. However, this hypothesis is inconsistent with the random pattern of occurrence of nitrogen fixation among various lineages of living bacteria (including the cyanobacteria), rather than a pattern of universal occurrence that is expected on the basis of an ancient origin. Within the Cyanobacteria, there are approximately nine evolutionary lineages. One of these, the heterocystous nitrogen-fixing cyanobacteria possesses heterocyst cells - a unique adaptation for spatially excluding oxygen. The heterocystous lineage of cyanobacteria is well suited for a pilot study on the evolution of nitrogen fixation (nif) genes. Ribosomal DNA sequences (23S ribosomal RNA genes) will be used to determine the evolutionary history of the heterocystous lineage, as an independent framework to evaluate the DNA sequence evolution of one of the three nitrogen fixation genes, nifD. Ultimately, additional nitrogen fixation genes and other cyanobacterial lineages will be examined.

蓝藻是一种多样化的产氧、光合细菌，几乎栖息在每一个主要的水生和陆地生物群系——沙漠、淡水和海洋，包括温泉和亚北极和南极地区。蓝藻在贫瘠土壤和养分枯竭地区尤为重要，是通过固氮过程提供固定氮的主要来源。有些物种与多种植物形成共生关系，直接提供氮供植物吸收。蓝藻的历史可以追溯到近35亿年前。就谱系的寿命和对地球早期环境的影响而言，它们广泛地多样化，成为地球上最成功、最具生态意义的生物之一。人们普遍认为，蓝藻细菌通过含氧光合作用将地球的厌氧大气转化为有氧大气，这是导致地球上各种生命进化的关键事件。虽然通过光合作用的二氧化碳固定作用在生物进化的早期就出现了，但我们不知道氮固定作用是什么时候开始的。由于固氮酶被氧不可逆地灭活，因此有人提出固氮是一个古老的过程，在地球大气变成有氧之前就存在了。然而，这一假设与固氮在各种活细菌谱系（包括蓝藻）中随机发生的模式不一致，而不是基于古老起源的普遍发生模式。在蓝藻中，大约有九个进化谱系。其中之一，异囊固氮蓝藻拥有异囊细胞-一种独特的适应空间排除氧。蓝藻的异囊谱系非常适合于固氮（nif）基因进化的初步研究。核糖体DNA序列（23S核糖体RNA基因）将被用来确定异囊系的进化史，作为评估三种固氮基因之一nifD的DNA序列进化的独立框架。最终，额外的固氮基因和其他蓝藻谱系将被检查。