Figure 3.

Iron dilution during cell growth determined by MRI. (A) Cell density and (B) transverse relaxation time (T2) of iron-labeled S. aureus samples at different time points of the growth curve. Cell cultures were labeled with 5-nm citrate coated IONPs (1 μmol Fe/ml for 10⁸ cells). For MRI measurements bacterial samples at each time point were diluted to an initial cell concentration of OD 0.5 and were embedded in 500 μl 0.5% agarose. (C) T2 measurements of agarose embedded cell cultures labeled with different iron concentrations in a 1:2 dilution row: 1 μmol Fe/ml, 0.5 μmol Fe/ml, 0.25 μmol Fe/ml, 0.125 μmol Fe/ml, 0.063 μmol Fe/ml, 0.031 μmol Fe/ml, 0.016 μmol Fe/ml. 1:2 dilution steps of the initial iron concentration imitate the iron dilution caused by cell division cycles. Note that dilution step 5 in (C) corresponds with measurement at 3 h in (B).