Also, the observed up-regulation of the two genes within 15 to 20 min after establishment of iron starvation (Fig. 2) is in accord with previous observations made by Deneer and Potter (5), who detected a similar rapid induction of iron-repressible outer membrane proteins. The positions of ExbB monomer, ExbB(Δ195-243), and the proteolytic degradation products are noted on the right. Samples from liquid cultures and plates were collected at different time points for cell count determination. For each gene, cDNA dilution curves were generated and used to calculate the individual real-time PCR efficiencies (E = 10[−1/slope]). The geometric mean of the five internal reference genes was used to correct the raw values for the genes of interest. Understanding how bacteria survive and multiply in this hostile environment and which genes are involved in this process is a prerequisite for the rational design of novel approaches for the treatment and prevention of disease.