In vivo Mössbauer spectroscopy of iron uptake and ferrometabolism in Escherichia coli

Iron limited growth of microbes results in derepression of siderophore receptor and transport-systems which can be utilized for controlled and specific siderophore mediated⁵⁷Fe incorporation, yielding a suitable resonance nuclide concentration inside the cell. We have employed in vivo Mössbauer spectroscopy to analyze⁵⁷Fe siderophore uptake and to monitor time-dependent processes of microbial iron metabolism in E. coli. The cell spectra display the course of siderophore uptake and ferric ion metabolization with a time resolution which is merely limited by the time required for sample preparation. Since iron is present in many metabolic processes, the in vivo analysis of selected metabolites after siderophore uptake seems to be extremely tedious at a first glance. Surprisingly, only few components of iron metabolism are visible in the Mössbauer spectra, thus enabling their analysis. The intracellular distribution pattern of the main iron metabolites observed by this method differs from that derived from biochemical analyses. Based on the spectroscopic results, two hitherto unknown Fe^2+/3+ high-spin proteins have been isolated. Additional Mössbauer experiments suggest that the novel iron proteins are not restricted to E. coli. Rather, similar components are detectable in several bacterial and fungal systems, thus pointing to a general importance. The function of these proteins is currently being analyzed.