Figure 1.

Growth of (a) S.Tm (N = 15, n = 5) and (b) E. coli (N = 15, n = 8) upon supplementation of ferrous iron and holoferritin at rising iron concentrations. Utilization of apoferritin by (c) S.Tm and (d) E. coli in equal protein concentrations corresponding to holoferritin containing 5 and 50 µM of iron (0.0028 and 0.0282 µM apoferritin, respectively; N = 15, n = 5). The addition of apoferritin resulted in a very small increase in the iron content of the final solution, which we calculated to be 1.121 and 11.221 nM for the low and high apoferritin group, respectively. Growth of (e) S.Tm (N = 15, n = 5) and (f) E. coli (N = 15, n = 5) upon the addition of 50 µM iron as ferrous iron or holoferritin normalized to their respective control: For ferrous iron, IMDM alone, whereas for holoferritin, apoferritin in equimolar protein concentration was used for normalization. (g) The growth-promoting effect of apoferritin on S.Tm upon addition of a PIC. All cultures were grown aerobically in ambient air at 37 °C and were shaken at 200 RPM. Growth data were logarithmized and then normalized to their corresponding control. Graphs are depicted as mean ± SD. (a,b) Two-way ANOVA or (c,d) one-way ANOVA corrected for multiple comparisons with the Holm-Sidak post hoc test was used. (e–g) Student’s t-test was used (*: p < 0.05; **: p < 0.01; ***: p < 0.001, ****: p < 0.0001). N: number of biological replicates, n: number of experiments conducted, PIC: protease inhibitor cocktail.