FIGURE 7.

Competition of ethidium uptake by Anabaena sp. and the hgdD mutant by analysis of the extracellular ethidium. A, comparison of ethidium uptake in the absence (white) and presence (gray) of 125 μm erythromycin (ERY) as measured in Fig. 2. Lines represent least square fit analysis by E1 (Fig. 1). The k₁ (B) and k₋₁ rate (C) for different ratios between erythromycin and EB is plotted, and lines represent the least square fit to determine the IC₅₀ value indicated. Error bars, standard deviation.