FIG 2.

Microfluidic screening for potential ligands of Tlp1 using the Tlp344Tar207 receptor. (A) Examples of the distribution of E. coli cells expressing Tlp344Tar207 or Tar as the sole receptor in the observation channel of the microfluidic device, acquired before the addition of ligands as well as 30 min and 50 min after the addition of 20 mM formate at the source pore (scale bar: 100 μm). The x component (black arrow) indicates the direction up the concentration gradient of formate. The response is characterized by measurements of the fluorescence intensity (cell density) in the analysis region (150 × 300 μm) of the observation channel, which is indicated by a yellow rectangle. (B) Relative fluorescence intensity of E. coli cells expressing Tlp344Tar207 as the sole receptor in the analysis region of the observation channel at 50 min after the addition of the indicated formate concentrations at the source or without ligand (buffer). (C) Relative fluorescence intensity of E. coli cells expressing Tar as the sole receptor in the analysis region of the observation channel 50 min after the addition of the indicated formate concentrations at the source or without ligand (buffer). In panels B and C, the corresponding values of the fluorescence intensities in the analysis regions were normalized to the fluorescence intensity of the cells in the buffer to obtain the chemotactic index. Error bars indicate the standard errors of three replicates. The P values were calculated using a paired t test. *, P < 0.05; **, P < 0.01, compared to the buffer.