All known microorganisms with the exception of lactobacilli display an absolute requirement for iron. Although iron is the fourth most abundant element on earth, it is rapidly oxidised at neutral pH forming insoluble hydroxides. To overcome this limitation, microorganisms have developed a plethora of mechanisms to acquire iron. Sinorhizobium meliloti 2011, the endosymbiont of Medicago sativa, produces one known siderophore, rhizobactin 1021. Due to the high demand for iron in the nodule, the iron acquisition mechanisms of S. meliloti 2011 have been subject to particular interest. Rhizobactin 1021 is structurally similar to aerobactin, which is produced by various pathogenic bacteria In E. coli, aerobactin is transported at the inner membrane via the fhu system. The jhu system of E. coli was found to be sufficient to allow the transport of rhizobactin 1021 accross the inner membrane. A fhuC mutant was found to be defective in the transport of rhizobactin 1021. A novel permease, RhtX, was identified in S. meliloti and found to be involved in rhizobactin 1021 transport. Heterologous expression of RhtX in an E. coli JhuC mutant restored rhizobactin 1021 utilisation, but not aerobactin utilisation. A homologue of RhtX was identified in the opportunistic human pathogen P. aeruginosa. Mutation of the gznQ,fptX, was found to result in a deficiency in pyochelin utilisation in P. aeruginosa. P. aeruginosa was found to be capable of utilising the xenosiderophores rhizobactin 1021, schizokinen and aerobactin. A receptor mediating the transport of these siderophores was identified and characterised. S. meliloti 2011 has also been found to be capable of acquiring iron from haem compounds, a characteristic generally found only amongst pathogens. A number of putative haem acquisition loci were identified in S. meliloti 2011 and were subject to analyses. The protein encoded by Smc02726 was identified as the receptor for haemin and haemoglobin under free living conditions.