Cyclic Glucan Biosynthesis and Phospholipid Metabolism of Bradyrhizobium

拟议研究的长期目标是进一步了解根瘤菌的类菌分化，这是豆科植物根部形成有效固氮根瘤的关键过程。一些证据表明，根瘤科的细胞膜成分在这种重要的微生物-植物共生中起着至关重要的作用。实验计划将集中在慢生根瘤菌细胞膜的磷脂和环状葡聚糖含量的表征上。此外，还将检测迟缓根瘤菌的磷脂代谢以及与这些细菌的环状葡聚糖生物合成相关的酶活性。实验基于申请人的初步研究，这些研究表明，根瘤科物种的磷脂代谢与这些细菌的环状葡聚糖的生物合成密切相关。拟议研究的一个重要方面将是检查慢生根瘤菌磷脂和环状葡聚糖的含量，在自由生活的微氧培养中诱导固氮后，水的可用性和结合或固定的来源氮是影响农业生产力的两个最重要的限制因素。因为农作物不能固定氮素，所以必须以固定的形式提供。这可以通过使用工业合成的氮肥来实现，然而，就化石燃料的支出而言，这种合成过程是一个非常昂贵的过程。另一种获取固定氮的机制已经进化出来，在这种机制中，某些植物能够参与到与固氮菌的复杂共生关系中。豆科植物和根瘤科植物之间的共生关系不仅是全球固定氮的重要来源，也是这种共生关系研究最充分的例子。该项目的总体目标是进一步了解根瘤菌的类菌分化--这是豆科植物根部成功形成固氮根瘤所必需的过程。

The long-term objective of the proposed research is to gain a further understanding of rhizobial bacteroid differentiation, a process essential for the development of effective nitrogen-fixing nodules on the roots of leguminous plants. Several lines of evidence have indicated that the cell- envelope composition of the Rhizobiaceae provides an essential function in this important microbial-plant symbiosis. The experimental plan will focus upon the characterization of the phospholipid and cyclic glucan oligosaccharide content of the cell-envelope of species of Bradyrhizobium. In addition, the phospholipid metabolism of the bradyrhizobia will be examined as well as the enzymic activities associated with the biosynthesis of the cyclic glucans of these bacteria. Experiments are based upon preliminary studies by the applicant that have indicated that the phospholipid metabolism of species of the Rhizobiaceae is intimately linked to the biosynthesis of the cyclic glucans of these bacteria. An important aspect of the proposed studies will be the examination of bradyrhizobial phospholipid and cyclic glucan content before, during, and after the induction of nitrogen-fixation in free-living microaerobic cultures.%%% The availability of water and a source of combined or fixed nitrogen represent the two most limiting factors in agricultural productivity. Because crop plants are not able to fix nitrogen, it must be provided in fixed form. This may be accomplished through the use of industrially synthesized nitrogen fertilizer, however, this synthetic process represents a very costly one in terms of the expenditure of fossil fuels. An alternative mechanism for acquiring fixed nitrogen has evolved in which certain plants are able to participate in a complex symbiotic relationship with nitrogen-fixing bacteria. The symbiotic relationship between leguminous plants and members of the family Rhizobiaceae represents not only an important source of globally fixed nitrogen, but also the most well-studied example of such symbiosis. The overall goal of this project is to gain further understanding of rhizobial bacteroid differentiation - a process essential for the successful development of nitrogen- fixing nodules on the roots of leguminous plants.***//