Genomic insights into the iron uptake mechanisms of the biomining microorganism Acidithiobacillus ferrooxidans

Abstract Iron (Fe) is an essential micronutrient that is frequently inaccessible to plants. Rice (Oryza sativa L.) plants employ the Combined Strategy for Fe uptake, which is composed by all features of Strategy II, common to all Poaceae species, and some features of Strategy I, common to non-Poaceae species. To understand the evolution of Fe uptake mechanisms, we analyzed the root transcriptomic response to Fe deficiency in O. sativa and its wild progenitor O. rufipogon. We identified 622 and 2,017 differentially expressed genes in O. sativa and O. rufipogon, respectively. Among the genes up-regulated in both species, we found Fe transporters associated with Strategy I, such as IRT1, IRT2 and NRAMP1; and genes associated with Strategy II, such as YSL15 and IRO2. In order to evaluate the conservation of these Strategies among other Poaceae, we identified the orthologs of these genes in nine species from the Oryza genus, maize and sorghum, and evaluated their expression profile in response to low Fe condition. Our results indicate that the Combined Strategy is not specific to O. sativa as previously proposed, but also present in species of the Oryza genus closely related to domesticated rice, and originated around the same time the AA genome lineage within Oryza diversified. Therefore, adaptation to Fe2+ acquisition via IRT1 in flooded soils precedes O. sativa domestication.

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

Microbiology ◽

10.1099/mic.0.27581-0 ◽

2005 ◽

Vol 151 (6) ◽

pp. 2005-2015 ◽

Cited By ~ 27

Author(s):

R. Quatrini ◽

C. Lefimil ◽

D. S. Holmes ◽

E. Jedlicki

Keyword(s):

Gene Expression ◽

Stress Responses ◽

Acidithiobacillus Ferrooxidans ◽

Iron Uptake ◽

Ferric Iron ◽

Sequence Similarity ◽

Cross Reactivity ◽

Mobility Shift ◽

E Coli ◽

Protein Levels

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. FurAF 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. FurAF 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. FurAF 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.

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