Iron Uptake Kinetics and Magnetosome Formation by Magnetospirillum gryphiswaldense as a Function of pH, Temperature and Dissolved Iron Availability

Abstract

The dynamics of iron uptake and magnetosome formation by the magnetotactic bacteria (MTB) Magnetospirillum gryphiswaldense was investigated at a broad range of pH, temperature and iron availability to evaluate the role of MTB in the iron biogeochemical cycle. Except at pH 5.0, all incubations have shown significant bacterial growth. However, magnetosome formation was limited at pH 8.0 and 9.0 as well as at 4°C, 10°C and 35°C. At optimal conditions (i.e., pH 7 and 28°C), the uptake rates of dissolved Fe(III) as a function of initial Fe concentration can be described by a Michaelis-Menten-type kinetic model with a maximum iron uptake rate, V_{max ,}, of 11 × 10⁻¹² μmoles cell⁻¹ h⁻¹ and an affinity constant, K_s of 26 μM Fe. High resolution imaging of magnetosomes synthesized at the different pH values, revealed a large range of morphologies and sizes, which illustrate the impact of environmental conditions on the formation of magnetite crystals by MTB.

Keywords:

• magnetotactic bacteria
• iron dynamics
• biomineralization
• magnetite characteristics

ACKNOWLEDGMENTS

Thanks are due to the FP6 Marie Curie MIR-EST “Mineral-Fluid Interface Reactivity” Early Stage Training Network (MEST-CT-2005-021120) and the UK NERC “Weathering Science Consortium” (NE/C004566/1) for financially supporting the work. We also like to acknowledge LEMAS (the Leeds Electron Microscopy and Spectroscopy Center) for granting access to the electron microscopy and analysis facilities. Finally, we would like to acknowledge two anonymous reviewers whose contributions have greatly improved the manuscript.