Effects of various concentrations of OHL on expression of cepI::luxCDABE, zmpA::luxCDABE, and cepR::luxCDBAE fusions. Expression of promoter-luxCDABE fusions was measured throughout growth in LB medium containing 100 μg/ml trimethoprim supplemented with different concentrations of OHL. The values are the means for triplicate cultures. (A) cepI::luxCDABE. (B) zmpA::luxCDABE. (C) cepR::luxCDABE. ▪, K56-2; ▴, K56-dI2; •, K56-dI2 with 300 pM OHL; □, K56-dI2 with 30 pM OHL; ▵, K56-dI2 with 3 pM OHL; ▿, K56-dI2 with 300 fM OHL; ⋄, K56-dI2 with 30 fM OHL.