The ferric iron uptake regulator (Fur) from the extreme acidophile Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is a Gram-negative bacterium that lives at pH 2 in high concentrations of soluble ferrous and ferric iron, making it an interesting model for understanding the biological mechanisms of bacterial iron uptake and homeostasis in extremely acid conditions. A candidate fur_AF (Ferric Uptake Regulator) gene was identified in the A. ferrooxidans ATCC 23270 genome. Fur_AF has significant sequence similarity, including conservation of functional motifs, to known Fur orthologues and exhibits cross-reactivity to Escherichia coli Fur antiserum. The fur_AF gene is able to complement fur deficiency in E. coli in an iron-responsive manner. Fur_AF is also able to bind specifically to E. coli Fur regulatory regions (Fur boxes) and to a candidate Fur box from A. ferrooxidans, as judged by electrophoretic mobility shift assays. Fur_AF represses gene expression from E. coli Fur-responsive promoters fiu and fhuF when expressed at high protein levels. However, it increases gene expression from these promoters at low concentrations and possibly from other Fur-regulated promoters involved in iron-responsive oxidative stress respon.