Figure 3

E. coli MG1655 pgi-EDP luxS produces extracellular AI-2 activity. (A) Conventional V. harveyi BB170 bioassay [17] with E. coli DH5α culture supernatants obtained from cultures growing in LB + 0.5% (w/v) glucose. Turquoise, grey, pink, bright green, dark green, blue, and red lines indicate the bioluminescence observed for E. coli DH5α culture supernatants after 0, 1, 2, 3, 4, 5, and 6 h of growth, respectively. Open circles, negative control (LB medium + 0.5% glucose); closed circles, AI-2 containing positive control (E. coli MG1655 culture supernatant after 3 h of growth). (B) Modified V. harveyi BB170 bioassay with the same E. coli DH5α culture supernatants as analysed in (A). 25 mM HEPES was present in the bioassay medium to prevent acidification. For figure legends, see (A). (C) Growth (lines) and AI-2 activity profiles (bars) for E. coli MG1655 luxS (blue) and E. coli MG1655 pgi-EDP luxS (red). Each strain was grown in LB medium + 0.5% (w/v) glucose and samples removed hourly. For each sample the optical density at 600 nm was recorded and AI-2 activity in culture supernatants recorded using the modified V. harveyi BB170 bioassay containing 25 mM HEPES. Results represent the mean of three independent bioassays. For AI-2 activity, error bars represent the standard deviations. The experiments were repeated five times with similar results.