The ability of bacteria to concentrate minerals is well known, but little is known about the subcellular distribution of ions. Electron probe microanalysis, X-ray mapping and electron energy loss spectroscopy of ultrathin cryosections are particularly suitable for determining composition at the ultrastructural level in cells, including bacterial spores. In the present study, we report preliminary experiments with these methods on elemental concentrations and distribution in E. coli B, including differences in the calcium content between dividing and non-dividing cells.E. coli B were grown in the presence of 1% tryptone (DIFCO), 0.2% glucose and 0.1M NaCl. The cells were harvested at a concentration of ∽3x108 cell/ml (in the late log phase). Cells were washed in nominallv ion-free solutions and then frozen, in the presence of 10% PVP, in supercooled Freon 22 at -164°C. The specimens were freeze-dried and cryosectloned as described previously. Analyses were performed on a Gatan LN2 cold specimen holder, at a temperature of -101°C. A bright-field image of the cryosectioned E. coli is shown in Fig. 1.
Calcium measurements with electron probe X-ray and electron energy loss analysis.