FIG. 5.
Bacterial acquisition of iron from NE-Tf and NE-Lf complexes. Lower panels show viable counts of E. coli strain E2348/69 grown in serum-supplemented SAPI medium after 18 h of incubation from an inoculum of 102 CFU/ml; upper panels show uptake of radioactivity (55Fe or 3H) associated with the 1-ml cultures shown in the lower set of histograms, i.e., radiolabel per 108 CFU (approximately); the values shown are the means of triplicate assays. Assay conditions were (a) SAPI medium containing 55Fe-labeled serum, (b) serum-SAPI medium supplemented with [55Fe]Tf (105 cpm), (c) serum-SAPI medium supplemented with [55Fe]Lf (105 cpm), and (d) unlabeled serum-SAPI medium. Unlabeled NE was used in assays a to c; 1 μCi of [3H]NE plus 50 μM unlabeled NE was used in assay d. In each case, bacteria were incubated in the absence of NE (control), in the presence of 50 μM NE (NE), or in the presence of 50 μM NE plus 200 μM Fe(NO3)3(NE+Fe).