SGER: Vector-Transformation System for Frankia

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Johnson 9724800 Biological nitrogen fixation is a key segment of the nitrogen cycle. The ability to carry out this reaction is limited to a very small number of prokaryotes. A sub-set of these have the capacity to form symbiotic relationships with higher plants to facilitate the process. Bacteria in the genus Rhizobia, gram-negative rods, are the most prominent member of this group of organisms. The genetics and biochemistry of nodulation and nitrogen fixation have been intensively investigated in Rhizobia. This is largely because of the plethora of genetic tools applicable to this group of organisms as well as their relationships with many important crop plants. Frankia are the other major bacterial contributor to symbiotic nitrogen fixation. These organisms are gram positive, filamentous bacteria that nodulate a wide variety of woody plants and shrubs. Superficially, the two types of bacteria have similar modes of operation. However, there are numerous fundamental differences which have been identified between the two systems. Because the Frankia are very slow growing and do not form symbioses with commercially important plants, our knowledge of their genetics and biochemistry is extremely meager. The lack of a vector-transformation system for these bacteria has seriously hampered attempts to understand their molecular biology. Now, the availability of Frankia promoters and the development of electroporation technology as well as highly sensitive, fluorescent DNA and protein probes makes feasible a systematic analysis of the many individual steps in both vector development and transformation that need to be done in order to allow genetic analysis of this important group of ntirogen-fixing bacteria.