Characterization of rhizobium genes involved in competition and survival in the rhizosphere

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Characterization of Rhizobium Genes Involved in Competition and Survival in the Rhizosphere Rhizobium is a Gram-negative soil bacterium that interacts with legumes to produce nitrogen fixing nodules on the roots of legumes thus allowing the plant to live under nitrogen deficient regimes.  Although a great deal is known about the genetics of nodulation, very little is understood about how bacteria survive/thrive in the soil environment prior to nodulation.  This research proposal will address this latter problem employing a genetic/biochemical approach.  The genome of  Sinorhizobium meliloti is sequenced and has been adopted as a model bacterium in which to study plant-microbe interactions.  The majority of the work in this proposal will be carried out in this system.  The work involves the genetic and biochemical characterization of genes that degrade  rhamnose, a plant derived sugar, that is necessary for Rhizobium to compete effectively for nodulation.  The results of our work in this area have led us to find a novel plant phenotype that is associated with a central metabolic pathway mutant.  The phenotype suggests that it is possible to increase the yield of the host legume under laboratory conditions.  To more fully understand this central metabolic pathways of S. meliloti are also being studied.  It is hoped that by understanding the fundamental biology of Rhizobium the knowledge generated may be relevant to enhancing biological nitrogen fixation.