FIG. 6.

The concentration of ornibactin in K56-2-conditioned succinate medium was determined. (A) Dilutions of the ornibactin stock solution were assigned activity in the CAS assay. (B) Dilutions of K56-2-conditioned medium, shown as the percentage of conditioned medium in water added to the CAS assay, were assigned CAS activity. (C) Known ornibactin concentrations (squares) and the volumes of conditioned medium that corresponded to the known ornibactin concentrations (diamonds) were tested for induction of fusion I. Values are the averages of data from three separate experiments (error bars indicate SD). The volume differences were made up with buffered medium (minimal medium lacking succinate) and were mixed 1:1 with fresh succinate medium.