Figure 3

E. coli cells expressing the Pph protein are unable to respond to aspartate. (A) The chemotactic response to aspartate of E. coli MM500 cells expressing the various Pph-derived proteins was investigated with a chemotactic chamber. The chemotactic inhibition (CI) was calculated as described in Materials and Methods. The CI-value of cells grown in the presence of fructose (hatched columns) was about 0.35, whereas cells grown in the presence of arabinose and expressing the Pph or the Pph-H670A protein (white columns) were calculated to 0.73 or 0.58, respectively. The error bars indicate the standard deviations of three independent experiments. (B) E. coli cells with pBAD-Pph were incubated for the indicated times with 0.2% arabinose or 0.2% fructose, respectively, and their chemotactic response to aspartate was investigated in a chemotactic chamber. The chemotactic inhibition rate was calculated after induction either with fructose (hatched columns) or arabinose (white columns) for the indicated time points. The error bars indicate the standard deviations of three independent experiments. The protein expression profiles (inlet) were analysed at 10 min (lanes 1, 2), 40 min (lanes 3, 4) and 60 min (lanes 5, 6) after induction. The odd numbered lanes are the non-induced controls.