Team:BCCS-Bristol/Calendar-Notebook/6 August 2008



BioBrick Transformation
Last Thursday, the primers VF2 and VR arrived. These primers allow a confirmation of a succesful transformation of most BioBrick parts by means of PCR. The resulting fragment length depends on the specific BioBrick DNA.

Using VF2 and VR, a colony PCR are was conducted with all colonies that were obtained with chemical competent cells so far. Two colonies with the yeast ADH1 promoter (No. 1 and 2, see left photo) and three colonies with a GFP generator (No. 3-5, see left photo) were identified as positive. Thus, all colonies are positive, but the transformation efficiency is too low, since the result was only one or zero colonies per transformation attempt.

Electroporation should give higher efficiencies. An attempt with a new BioBrick (ADH1 terminator) resulted in 69 colonies! Ten of them were analysed using PCR. The resulting fragment should have a length of 461 bp, but from the eigth positive colonies fragments between 650-750 bp were obtained (see right photo). This is probably due to a mutation which might result in a different binding location for one of the primers. Another explanation might be that the denoted length is wrong. Since this BioBrick is not important for our project, it will be disregarded.

The transformation efficiency of the electroportation was significant higher than of the chemical competent cells. Therefore, an own stock of electric competent cells was made.

Agar plug assay
TR235 (E. coli with construct to detect adhesion to hydrophobic surfaces) arrived from Princeton (Thomas J. Silhavy). Cells are viable, growth curve done. 11µm PS beads shown to be moved by bacteria (MG1655); we observed ‘jiggling’ of beads when bacteria present (not seen in no-bacteria control). Also, we observed significant movement in different directions (distances of approx 1x to 5x length of the beads by eye) of beads that were close together, suggesting that movement was not due to currents in the medium. We saw no distance covered in almost all the control beads, a few moved small distances, so some currents are present. Bacteria and beads were left together for ~30mins to allow time for adhesion. No movement has yet been seen when the bacteria and beads are not left to adhere. We will look again at this, as we may have not previously looked closely enough (photographing over a time course of a few minutes).

Chemotaxis assay (Yu, H.S. et al. (1997) FEMS Microbiology Letters, 156, 265-269.) has not worked so far. Currents can be seen flowing from the aspartate plug, pushing bacteria away. The focus of this week will be on getting this fixed, with a view to combining chemotaxis and the ability to move beads, allowing us to move beads in a particular direction.

The GRN for switching on the chemotactic response by binding to a bead, and signaling to nearby bacteria that a particle is in the vicinity, is almost finalised.