A homologue of the ferric uptake regulator gene, fur, was identified from a Azospirillum brasilense Sp7 genomic DNA clone. Experiments performed with transcriptional lacZ fusions demonstrated that the A. brasilense fur homologue regulated the expression of two fur regulated Escherichia coli genes: fiu (ferric iron uptake) and fhuF (ferric hydroxamate uptake). A differential regulation by the cognate Fur and the heterologous Fur homologue in response to the iron status of the growth medium was also observed.