Fig 3. The abundance of iron stimulates the HPI during motility.

(A) qPCR for the HPI genes ybtA, irp2 and fyuA in NU14 wild type strain showed equal transcription rates for both iron depletion in NBD and during motility on LB soft agar plates. (B) The supplementation of 0.3% LB soft agar plates with 10 μm Fe(III)Cl₃ resulted in increased motility (*p<0.05). The addition of 100 μM or 1 mM Fe(III)Cl₃ did not affect motility diameters significantly. (C) qPCR of swarming NU14 on LB soft agar plates supplemented with different concentrations of Fe(III)Cl₃. Only addition of 10 μm Fe(III)Cl₃ led to the increased gene expression of the HPI genes ybtA, irp2 and fyuA. The transcription of fliC was stronger upregulated during motility with the addition of iron, but displayed no difference for various concentration of Fe(III)Cl₃. (D) Western blot analysis of the expression of YbtA, FyuA and flagellin on LB soft agar plates supplemented with different concentrations of iron. YbtA and FyuA expression was only increased for 10 μM Fe(III)Cl₃. The addition of 1 mM ferric iron repressed almost completely expression of YbtA and FyuA. Rising concentrations of iron led to an overall enhanced expression of flagellin with no difference for various concentrations.