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.***//
