Siderophores are small, iron chelating molecules produced by many bacteria to help meet the iron requirements of the cell. Multiple metabolic functions require iron as it serves as a cofactor in many enzymes and cellular processes. However, in the presence of oxygen and at physiologic pH, iron forms insoluble ferric complexes that cause the nutrient to be unavailable to bacterial cells. Siderophores alleviate this limitation by chelating the ferric iron, rendering it soluble and available for uptake. One group of microorganisms known for their ability to produce siderophores is the rhizobia. These bacteria are characterized both by their formation of symbiotic relationships with leguminous plants and their ability to fix atmospheric nitrogen. Rhizobium leguminosarum ATCC 14479, which infects the red clover Trifolium pratense, was found to produce a trihydroxamate siderophore. Purification and chemical characterization identified this siderophore as Vicibactin that has been found to be produced by other rhizobial strains.

Siderophores are low molecular weight, iron chelating compounds produced by many bacteria for uptake of iron in case of iron scarcity. Vicibactin is a trihydroxamate type siderophore produced by Rhizobium leguminosarum bv. trifolii ATCC 14479. This work focuses on identifying an outer membrane receptor involved in the transport of vicibactin. We have confirmed the presence of the putative fhuA gene in R. leguminosarum bv. trifolii ATCC 14479. This bacteria shows mutualistic symbiosis with the red clover plant Trifoliium prantense. Leghemoglobin, with its cofactor heme is present in the plant root nodules that surrounds the infecting organism present in the nodules. This work attempts to elucidate the ability of Rhizobium leguminosarum bv. trifolii ATCC 14479 to utilize heme-bound iron and genes involved in the transport. We have also elucidated the role of energy transducing proteins TonB- ExbB-ExbD on the heme-bound iron uptake system.