FIG 6.
TonB is required for Mcc1229 activity. The periplasmic energy-transducing protein TonB was deleted from E. coli O157:H7 strain EDL933 by one-step recombination. The resulting mutant does not increase Stx expression in response to spent supernatants containing Mcc1229. Activity is restored upon complementation with a plasmid copy of tonB, carried on pKP315 (tonB+). EDL933ΔtonB (E) represents the empty vector strain, which carries pBAD24. Because tonB is under ParaC control on pKP315, all strains in this experiment were grown in the presence of arabinose. Asterisks mark significant differences between a given supernatant sample and the EDL933 wild type (two-way ANOVA and Dunnett’s multiple-comparison test).