Fig. 9.

Addition of apo-Ybt or culture supernatants containing Ybt stimulates the growth of the ΔznuBC Δpsn irp2∷kan mutant. A. After acclimation to growth at 37°C in cPMH2 supplemented with 0.6 μM ZnCl₂ and 1.0 μM FeCl₃, cultures were then back diluted to an OD₆₂₀ of ∼0.1 in a 1:1 mixture of the same medium with culture supernatants. B. Alternatively, similarly grown cultures of the ΔznuBC Δpsn irp2∷kan mutant were back diluted to an OD₆₂₀ of 0.1 and incubated with apo-Ybt (μM Ybt) or ethanol solvent (0 μM Ybt). Culture optical densities were measured after overnight incubation at 37°C. Strains KIM6-2077.18 (ΔznuBC Δpsn irp2∷kan; labeled YbtX⁺) and KIM6-2077.19 (ΔznuBC Δpsn irp2∷kan ΔybtX; labeled YbtX^-) were tested for growth with supernatants from KIM6+ (Ybt +) and KIM6-2046.1 (irp2∷kan; Ybt -) (Panel A and B) or apo-Ybt (Panel B). Addition of apo-Ybt to a final concentration of 1.7 μM is equivalent to the Ybt present in cultures with at a 1:1 mixture with supernatant from KIM6+. NA – not applicable. Data presented for the YbtX⁺ strain are averages from 10 independent experiments with 6 independent culture supernatants (panel A) or 3 independent experiments (panel B). Data presented for the YbtX^- strain are averages from two or more independent experiments supplemented with 2 independent culture supernatants (panel A). Error bars represent standard deviations while asterisks with brackets indicate statistical significances calculated using the Student's two tailed t-test (p = <0.001 - ***; p = <0.05 - *).