Iron nutrition and physiological responses to iron stress in Nitrosomonas europaea
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Nitrosomonas europaea, as an ammonia-oxidizing bacterium, has a high Fe requirement and has 90 genes dedicated to Fe acquisition. Under Fe-limiting conditions (0.2 μM Fe), N. europaea was able to assimilate up to 70% of the available Fe in the medium even though it is unable to produce siderophores. Addition of exogenous siderophores to Fe-limited medium increased growth (final cell mass). Fe-limited cells had lower heme and cellular Fe contents, reduced membrane layers, and lower NH3- and NH2OH-dependent O2 consumption activities than Fe-replete cells. Fe acquisition-related proteins, such as a number of TonB-dependent Fe-siderophore receptors for ferrichrome and enterobactin and diffusion protein OmpC, were expressed to higher levels under Fe limitation, providing biochemical evidence for adaptation of N. europaea to Fe-limited conditions.
KeywordsNitrosomonas europaea Iron metabolism Iron stress Siderophore receptors
High performance liquid chromatography tandem mass spectrometry
We thank Dr. B. Dubbels for his insightful discussions, B. Arbogast (Central Laboratory, OSU) for help with the HPLC/MS/MS analysis, and M. Nesson for help with electron microscopy (Electron Microscope Facility, Department of Botany and Plant Pathology, OSU). We appreciate the help of A. Ungerer (College of Oceanic and Atmospheric Sciences, OSU) for Fe determination by ICP-MS. This research was supported by grant DE-FG03-01ER63149 to DJA.
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