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

1 Laboratory of Bioinformatics and Genome Biology, University of Andrés Bello, Santiago, Chile 2 Millennium Institute of Fundamental and Applied Biology, Santiago, Chile 3 Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile Correspondence D. S. Holmes dsholmes2000{at}yahoo.com 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 ( F erric U ptake R egulator) 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 responses. Abbreviations: EMSA, electrophoretic mobility shift assay; Q-PCR, quantitative PCR The GenBank/EMBL/DDBJ accession number for the sequence reported in this paper is AY465905 . A comparison of the predicted amino acid sequence of A. ferrooxidans Fur AF with that of other micro-organisms, revealing the conservation of several motifs and structural features typical of the Fur family, is available with Supplementary Fig. S1 with the online version of this paper at http://mic.sgmjournals.org .