FIG. 5.

Solid-phase Tf discrimination assays. Iron-stressed whole gonococci were applied to nitrocellulose, and the ability to discriminate between different forms of Tf was assessed. In panel A, cells were incubated with HRP-Tf and varying amounts of competitor: N, no competitor; F, ferrated Tf; or A, apo-Tf. In panel B, cells were incubated with HRP-Tf and varying amounts of competitor: H,hTf; B, bovine Tf; or M, murine Tf. Competitor concentration decreases from left to right (solid arrows). All mutant strains were tested for Tf-binding specificity in the absence of TbpA. Each series of three rows is labeled according to strain name with the HA epitope insertion number in parentheses. FA19 serves as the wild-type control. FA6747 and FA6905 are the TbpA⁻ and TbpB⁻ controls, respectively.