Mössbauer spectroscopy of Escherichia coli and its iron-storage protein

57Fe Mössbauer spectra of whole frozen Escherichia coli cells and of an iron storage protein isolated from iron-rich cells of E. coli have been measured over a range of temperatures down to 0.08 K. The spectra of E. coli cells with high iron content and of the iron storage protein were found to be very similar. Above 4 K these spectra consist of a quadrupole split doublet characteristic of Fe3+. Below 3.5 K, the spectra display magnetic hyperfine splitting which is temperature dependent, and point to the existence of an ordered magnetic phase associated with a saturation magnetic hyperfine field of 43 tesla in both samples. The results indicate that the bulk of iron in the iron-rich cells is in the form of aggregates similar in nature to the iron cores in the isolated protein, although the latter account for not more than 1% of the total iron in the cells. The Mössbauer spectra of the isolated protein are different from those observed in ferritin, the iron-storage protein of plants and higher animals, showing that the iron cores in these two proteins are different.