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

这项美国-巴西项目将支持亚利桑那大学的Christina Kennedy和EMBRAPA在巴西里约热内卢的Johanna Dobereiner的合作。该项目旨在分离和突变重氮养偶氮杆菌的酶活性所需的基因。固氮细菌已经从巴西的甘蔗品种中分离出来，其中高达70%的植物总氮来自大气氮（二氮）。分离的主要生物，重氮营养菌，是一种内生菌，被认为负责固定二氮和将产物转移到植物系统。研究人员将使用不能固定氮的突变体来证明或反驳该物种在甘蔗中提供固定氮的作用。他们还将描述参与细菌对环境因素（如控制氮酶生物合成的氨和氧）反应的基因。增加提供给植物的固定氮量的策略将用于构建在氨存在下产生氮酶或对氧耐受性增强的菌株。美方在固氮细菌遗传学方面有专长。巴西实验室是发现重氮营养菌的地方，目前正在研究重氮营养菌在植物中的定殖。双方都将从确定一种新的和潜在的重要固氮细菌物种的意义中受益。＊＊＊

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. ***