FIG 2.

Purified Fe(III)-Ybt and Cu(II)-Ybt exhibit opposing effects on Ybt production. Cultures were grown with a ¹³C-substitute carbon source so that de novo Ybt biosynthesis could be distinguished using mass spectrometric quantification. Addition of 3 μM unlabeled Fe(III)-Ybt decreased [¹³C]Ybt concentrations in UTI89 culture supernatants but had an insignificant effect on [¹³C]Ybt in UTI89Δfur supernatants. Addition of 3 μM unlabeled Cu(II)-Ybt increased [¹³C]Ybt concentrations in both UTI89 and UTI89Δfur culture supernatants. Data were plotted from a representative experiment as percent mean area ratio ± SD from triplicate determinations. ns, nonsignificant; *, P = 0.0045; ****, P < 0.0001 according to Dunnett’s multiple-comparison test.