PUB - Publikationen an der Universität Bielefeld

The Rhizobium meliloti C-4-dicarboxylate transport (Dct) system is essential for an effective symbiosis with alfalfa plants. C-4-dicarboxylates are the major carbon source taken up by bacteroids. Genetic analysis of Dct-mutant strains led to the isolation of the dct carrier gene dctA and the regulatory genes dctB and dctD. The carrier gene dctA is regulated in free-living cells by the alternative sigma factor RpoN and the two-component regulatory system DctB/D. In addition, DctA is involved in its own regulation, possibly by interacting with DctB. In bacteroids, besides the DctB/DctD system an additional symbiotic activator is thought to be involved in dctA expression. Further regulation of dctA in the free-living state is reflected by diauxic growth of rhizobia, with succinate being the preferred carbon source. The tight coupling of C-4-dicarboxylate transport and nitrogen fixation is revealed by a reduced level of C-4-dicarboxylate transport in nitrogenase negative bacteroids.