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Iron-uptake in the Euryarchaeon Halobacterium salinarum
Dirk Hubmacher1, Berthold F Matzanke, Stefan Anemüller
1Department of Anatomy and Cell Biology, McGill University of Montreal, 3640 University Street, Montreal, QC, Canada H3A 2B2.
Summary
This study reveals how Halobacterium salinarum, an archaeon, transports iron. It shows an energy-dependent iron uptake mechanism, suggesting metal reduction at the membrane.
Area of Science:
- Microbiology
- Biochemistry
- Extremophile Biology
Background:
- Iron uptake mechanisms are well-understood in prokaryotes and eukaryotes, but less so in Archaea.
- Archaea, including Halobacterium salinarum, inhabit extreme environments, necessitating unique biological processes.
- Understanding iron transport in extremophiles like H. salinarum is crucial for comprehending their survival strategies.
Purpose of the Study:
- To elucidate the iron transport mechanism in the extremely halophilic Euryarchaeon Halobacterium salinarum strain JW 5.
- To investigate the role of siderophores and other chelators in iron acquisition for H. salinarum.
- To characterize the kinetics and energy dependence of iron uptake in this archaeon.
Main Methods:
- Culturing H. salinarum under low-iron conditions and analyzing culture supernatants for siderophores.
- Growth experiments using various xenosiderophores to assess their utilization by H. salinarum.
- [55Fe]-[14C] double-label experiments to track iron and chelator uptake.
- Inhibition studies using cyanide and gallium (Ga) to probe the iron transport pathway.
- Determination of kinetic parameters (K(M) and Vmax) for iron uptake.
- Measurement of [55Fe]-uptake kinetics in the presence and absence of Ga.
Main Results:
- No siderophores were detected in H. salinarum culture supernatants under low-iron conditions.
- H. salinarum demonstrated growth support from various xenosiderophores, indicating their potential utilization.
- The organism actively took up iron ([55Fe]) but not the chelator citrate.
- Iron uptake was inhibited by cyanide and, at high concentrations, by gallium.
- Kinetic analysis revealed a K(M) of 2.36 microM and Vmax of approximately 67 pmol Fe/min/mg protein for iron uptake.
- High concentrations of Ga only partially inhibited iron uptake.
Conclusions:
- Iron uptake in H. salinarum is an energy-dependent process.
- The results suggest that iron is reduced at the membrane level prior to or during transport.
- H. salinarum possesses a distinct iron acquisition system, potentially utilizing external chelators but not synthesizing its own siderophores.
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