U.S.-Brazil Cooperative Research: Genetic Analysis of Nitrogen Fixation in Acetobacter diazotrophicus, an Endophyte of Sugar Cane

9302788肯尼迪这个美国-巴西项目奖将支持亚利桑那大学的克里斯蒂娜·肯尼迪和巴西里约热内卢EMBRAPA的约翰娜·多贝莱纳的合作。该项目旨在分离和突变重氮营养固氮菌固氮酶活性所必需的基因。从巴西甘蔗品种中分离出固氮菌，在这些品种中，高达70%的植物总氮来自大气氮(氮素)。分离出的主要生物体是一种内生菌，被认为负责固定氮和将产物转移到植物系统。研究人员将使用无法固定氮素的突变体来证明或反驳该物种在甘蔗中提供固定氮素的作用。他们还将描述细菌对控制固氮酶生物合成的环境因素(如氨和氧气)的反应所涉及的基因。增加提供给植物的固定氮量的策略将被应用于构建在氨存在下产生固氮酶的菌株或具有更高的耐氧性的菌株。美方在固氮菌的遗传学方面拥有专业知识。巴西的实验室是重氮菌被鉴定的地方，它在植物上的定殖正在研究中。双方都将受益于确定一种新的、潜在重要的固氮细菌物种的重要性。***

9302788 Kennedy This U.S.-Brazil Program award will support the collaboration of Christina Kennedy of the University of Arizona and Johanna Dobereiner of EMBRAPA in Rio de Janeiro, Brazil. The project aims to isolate and mutate genes of Azobacter diazotrophicus necessary for nitrogenase enzyme activity. Nitrogen-fixing bacteria have been isolated from sugar cane varieties in Brazil in which up to 70 percent of total plant nitrogen comes from atmospheric nitrogen (dinitrogen). The major organism isolated, A. diazotrophicus, is an endophyte thought to be responsible for the fixation of dinitrogen and transfer of products to the plant system. The researchers will use mutants unable to fix nitrogen to prove or disprove a role for this species in providing fixed nitrogen in sugar cane. They will also characterize genes involved in bacterial responses to environmental factors such as ammonia and oxygen that control nitrogenase biosynthesis. Strategies to increase amounts of fixed nitrogen provided to plants will be applied to construct strains that produce nitrogenase in the presence of ammonia or have increased tolerance to oxygen. The U.S. side has expertise in the genetics of nitrogen-fixing bacteria. The Brazilian laboratory is where A. diazotrophicus was identified and its colonization of plants is being studied. Both sides will benefit from establishing the significance of a novel and potentially important nitrogen-fixing bacterial species. ***